In this article, I list all the estimates I could find for numbers of vertebrates that are farmed or kept in captivity for various purposes. I also describe some groups of captive vertebrates for which I found no estimates. For some bigger groups of animals that are less well-known amongst animal activists, I also describe trends and main welfare concerns.

The purpose of the article is to make it easier to find and compare estimates. Hopefully, this can also help animal advocates decide which issues to focus on. Note that I chose to focus on captive vertebrates simply to limit the scope of the article.

Summary tables

Estimates are summarized in the tables below. Numbers can also be explored in this spreadsheet. The rest of the article provides sources and explanations for these numbers.

All figures are for the whole world unless otherwise specified. For brevity, I use M for a million (10^6) and B for a billion (10^9).

Reptiles and amphibians

Fish

Note that all the numbers above exclude shellfish. I’ve found no estimates for :

• fish used as live bait in commercial fishing,
• fish trapped in nets and traps,
• fish hooked on hooks in commercial and recreational fisheries,
• food fish transported alive,
• other species of wild-caught fish suffocating in the air after landing.

Chickens

Most of the 68.8B slaughtered chickens were raised specifically for meat, but the figure seems to include at least some slaughtered chickens from the egg-laying industry (see the appendix in Šimčikas (2019a)). According to FAOSTAT, in total there were 23.7B chickens alive in 2018.

Other birds

I haven’t found estimates for the number of:

• ducks and geese live-plucked for their feathers and down,
• swiftlets farmed for their nests,
• ostriches farmed for meat

Mammals

I haven’t tried finding the number of:

• animals raised in other pet mills (kitten mills, rabbit mills, etc.),
• animals raised in more humane pet breeding facilities,
• household rodent pests caught in traps,
• civets used to make civet coffee,
• elk farmed for food.

Mixed species

I haven’t estimated the number of animals who are:

• kept alive in food markets,
• captured or captive-bred to be released into the wild as a Buddhist ritual to earn good karma (fangsheng),
• raised to be hunted in countries other than the UK,
• used in circuses outside of Europe,
• used for racing, fighting, and other forms of entertainment,
• kept in wildlife rehabilitation clinics,
• land animals bred in captivity to be released into the wild for species reintroduction programs.
• various species of animals kept in wildlife farms (see Standaert (2020))

Pets

The table below presents Euromonitor International data, which has estimates of the number of pets in 53 countries,^[1] which account for about 70% of the world’s human population.

If estimates in tables above seem difficult to compare and comprehend, it may be useful to look at the appendix where I convert estimates into units of time. Estimates can also be explored in this spreadsheet.

Explanation of uncertainty levels

In the ‘Uncertainty’ columns in the tables above, I describe the uncertainty for each estimate as low, moderate, high, or very high. Here is roughly what I mean by these words:

• Low - the estimate comes from a trustworthy source that explains how it arrived at the estimate. I’d be surprised if the estimate was off by a factor of 1.5 or more. In cases I provide a point estimate (e.g., “1M”), this means that I’d be surprised if the actual number was more than 1.5 times smaller or larger than the estimate. In cases where I provide a range (e.g., “1M–2M”), this means that I’d be surprised if the real number was more than 1.5 times larger than the upper bound or more than 1.5 times smaller than the lower bound.
• Moderate - I’d be surprised if the estimate was off by a factor of 2 or more.
• High - I’d be surprised if the estimate was off by a factor of 3 or more
• Very high - I’d be surprised if the estimate was off by a factor of 5 or more

Note that these are my subjective uncertainties. In many cases, I haven’t spent much time thinking about them, so they shouldn’t be taken too seriously.

The rest of this article explains the sources for all of the estimates in the tables above.

Reptiles and amphibians

Frog farming

Frogs are farmed mostly for their legs that are used as a delicacy food in many countries around the world. Warfield (2018) describes welfare problems in frog farms. It claims that farmed frogs suffer from overcrowding, lack of food, fighting with each other, cannibalism, diseases, fluctuating temperatures, poor water quality, and sanitation. Frog farming also causes important ecological problems (see Altherr, Goyenechea and Schubert (2011) and Ribeiro et al. (2019)).

According to FAO’s FishStatJ data, the world’s farmed frog production in 2017 was 100,379 tonnes in live weight, of which 91% was produced in China, 4.2% in Vietnam, and 1.6% in Taiwan. It seems^[2] that most of these frogs are American bullfrogs, but it’s unclear.

Mean slaughter weight for American bullfrogs seems^[3] to be somewhere between 175g and 300g (FAO, Ayres et al. (2015), Lutz and Avery (1999), Moreira, Henriques and Ferreira (2013)). If we assume that the mean slaughter weight for all frog species is between 100g and 350g and trust FAO’s 100,379 tonnes figure, we can estimate^[4] that 290M–1B frogs were slaughtered in 2017. In contrast, Gratwicke et al. (2010) estimates that between 0.8B–3.2B frogs are consumed by people each year. However, I think that Gratwicke et al. (2010) estimate is inaccurate due to a mistake.^[5]

American bullfrog slaughter age seems to depend greatly on an individual and species, but the mean seems to be somewhere between 4 months and 20 months.^[6] Based on this, we can estimate^[7] that 96.7M–1.67B frogs that will be slaughtered are alive in farms at any time (including tadpoles).

This estimation ignores frogs that die before the intended slaughter age. FAO claims that farmed American bullfrog stocks “can achieve a survivorship of more than 50 percent.” Furthermore, it mentions that tadpoles are routinely culled to lower competition. Moreira, Henriques and Ferreira (2013) observed a pond in Brazil and estimated that the mortality was 10% during the tadpole phase, 35% during metamorphosis and pre-fattening phases, and 10% during the fattening phase (that is about 53% during the entire life). To account for mortality, I subjectively increase the number of farmed frogs and frog tadpoles alive at any time from 96.7M–1.67B to 120M–2.5B.

See footnotes in this section for more details about the estimates. Note that these estimates are very rough, and I have very high uncertainty about them, especially the number of farmed frogs alive at any time.

Also, note that 2018 Tencent article predicts that the demand for frogs will grow rapidly in the next 3 to 5 years. Hence, my estimate (which is based on 2017 FAO data) may already be outdated. I’m also uncertain if FAO statistics I’m depending on are accurate.

Finally, note that the estimate is only for farmed frogs. Many frogs are wild-caught, and these frogs suffer during capture and slaughter. E.g., Altherr, Goyenechea and Schubert (2011) describes a practice of removing legs from living frogs with knives, scissors, or hands. Kusrini (2005) claims in 1999–2002, Indonesia exported 3.8 tonnes of frozen frog legs, which were harvested from an estimated 28M–142M wild-caught frogs. The author also claims that the number of frogs consumed within Indonesia could be seven times larger. In contrast, according to FAO’s FishStatJ data, Indonesia captured only 1.5 tonnes of frogs in live weight per year in 1999–2002. This suggests that either FAO or Kusrini (2005) statistics on wild-caught frogs are inaccurate.

Turtle farming

Turtles are farmed for food, as well as for medicinal products or to be kept as pets. (Gong et al. 2009)). They are mostly farmed in China. Various estimates show that their numbers may be substantial:

• According to the statistics in FAO’s FishStatJ, in 2017, there were 371,400 tonnes of turtles produced, of which 322,102 tonnes (87%) were Chinese softshell turtles raised in China.^[8] According to FAO, Chinese softshell turtles are harvested at the weight of “1.0-1.5 kg or more” and it takes them 1–2 years to reach this weight. Using this information, we can estimate that in 2017, there were roughly 180M–320M Chinese softshell turtles harvested, and 250M–550M alive at any time, in China. These numbers don’t account for pre-slaughter mortality.

• An alternative estimation can be made using the data in Haitao et al. (2008). The paper describes a 2002 survey which found that there were at least 309M turtles housed in 684 surveyed farms in China, of which 303M were Chinese softshell turtles. The surveyed farms sold about 125M Chinese softshell turtles with a combined weight of 91,382 t. Using this information and the 322,102 t figure from FAO, we can extrapolate that in 2017 in China there were 440M Chinese softshell turtles harvested, and 1.07B alive at any time.

• Gong et al. (2018) cites “a brochure printed for the 8th World Congress of Herpetology in China” to claim that 900M Chinese softshell turtle hatchlings are raised in Chinese turtle farms every year, more than double the turtles harvested annually in my extrapolations above.

• Cai et al. (2014) claim that in Guangdong province, there are 3.1M adult turtles who produce 52M baby turtles annually.

Haitao et al. (2008) also claims that most Chinese turtle farms operate illegally and are therefore not known by the government. If the situation hasn’t changed, FAO numbers could be an underestimate. This could help explain the gap between the 900M figure cited in Gong et al. (2018) and my extrapolations.

If the number of turtles harvested is twice as big, then the number of turtles alive may be twice as big as my estimates suggest as well. Hence, overall I think there are 180M–900M farmed turtles harvested every year, and 250M–2.14B alive at any time. Note that these numbers don’t account for pre-slaughter mortality.

One source that seems to contradict these numbers is the abstract of Zhou and Huang (2007). It claims that in December 2006, the stock of turtles in captivity in China was only 2M–4M and that 30M–40M hatchlings were produced (presumably per year). However, the article is relatively old, and I’m not sure if it covers all the turtles farmed for meat. The article doesn’t seem to even mention Chinese softshell turtles. (I can’t read the article in full because it’s written in Chinese).

Also, note that my estimates are only for one species of turtles and only for China. Turtles are also farmed in other countries. E.g., according to table 8 in the 2018 U.S. Census of Agriculture, 1.6M farmed turtles were sold in the U.S.

This video shows conditions in one turtle farm but I don't know if it is representative. The video also mentions that turtles are fed meat, fish and small shrimps.

Snake farming

Aust et al. (2017) claim that:

China and Viet Nam are considered to be the largest and most important producers of, and markets for, snake meat. Calculating the total size of the industry is difficult, although a conservative estimate for China and Viet Nam suggests there are at least 4,000 closed-cycle farms producing several million snakes of at least 15 taxa (CITES Management Authority, Viet Nam and Guangxi Forestry Administration, unpubl. data).

Willett (2013) claims that one Chinese village breeds 3M snakes per year for food and venom (which is used for medicinal purposes). Another article about the same village claims that there are over 6M snakes in the village, of which 4M are in a single farm. The article also mentions that dead chicks and frogs are used for feeding the snakes. I haven't found any other estimates of farmed snake numbers. Note that snakes are also farmed for their skins.

See this comment for some more discussion on what farmed snakes are fed.

Salamander farming

Cunningham et al. (2015) describes the Chinese giant salamander farming industry in China. It claims that these animals are an expensive delicacy in China. According to a 2012 estimate it cites, 70% of farmed Chinese giant salamanders were grown in Qinling Mountain region in Shaanxi Province. The article also claims that a 2011 census estimated that licensed farms in Shaanxi Province housed 2.6M salamanders (including hatchlings, juveniles and adults). It would follow that about 2.6M / 0.7 = 3.7M salamanders are being farmed in China at any time. However, Cunningham et al. (2015) claim that most of the farms are unlicensed. Hence the census of licensed farms didn’t capture the full scale of the industry. Furthermore, Salisbury (2015) claims that “the industry has expanded massively” since the census. Cunningham et al. (2015) also mention that the industry is rapidly growing. Consequently, the current number of farmed salamanders could be much higher.

Cunningham et al. (2015) claim in most cases, salamanders are fed farmed fish, but the use of farmed frogs was also reported. The paper also mentions that salamanders are often force-fed to speed up their growth.

Crocodile and alligator farming

Crocodiles and alligators are farmed for meat, leather, and other purposes.

AgriFutures Australia claims that “an average of 1.33 million crocodilians were harvested annually worldwide for the three years to 2010.” However, it doesn’t provide a source for the claim.

Perawongmetha (2017) claims “some 1.2 million crocodiles are kept on more than 1,000 farms in Thailand, according to figures from the Thai department of fisheries.” After a brief search, I couldn’t confirm this statistic.

According to Table 8 in the 2018 U.S. aquaculture census, there were 73,000 alligators sold whole in the U.S., down from 314,000 in 2013. However, the amount of alligator hides and meat produced has increased in the same period. Louisiana Department of Wildlife and Fisheries claims that Louisiana’s farmers harvest more than 280,000 farm-raised alligators annually. According to Shirley and Elsey (2015), in 2014, there were 37 production facilities in four states (Louisiana, Florida, Georgia, and Texas), and the total annual production was slightly more than 350,000 crocodiles.

While the numbers of farmed crocodiles and alligators are not huge, it could be that many more animals are killed to feed them. Brooks (2010) estimates that in Cambodia there are 32,999 to 159,376 farmed crocodiles, and they consume 2.7M–12.2M snakes per year. “Njeru (2016) claims that in Kenya, crocodiles are fed fish, blood-soaked maize, and other meats. Shirley and Elsey (2015) claims that in the U.S., they are fed high-protein floating pellets but doesn’t explain what they are made of. See this comment for a more in depth discussion of animals fed to farmed crocodiles and alligators.

Fish

Fish farmed for food

Estimates of the number of farmed food fish slaughtered annually:

• 51B–167B (source: Fishcount, based on 2017 data)
• 92.1B (source: Open Phil spreadsheet, based on 2016 data)

Estimates of farmed food fish alive at any time:[9]

• 73B–180B (source: Fishcount, based on 2015 data)
• 85.2B (source: Open Phil spreadsheet, based on 2016 data)

Open Phil’s estimate of farmed fish alive at any time takes into account fish who die before the intended slaughter age, while Fishcount's estimate does not. If OpenPhil didn’t take pre-slaughter mortality into account, their estimate of farmed fish alive at any time would be 72.5B, which is slightly lower than the lower bound of the Fishcount estimate. Reasons for the disagreement between the two estimates can be seen in the ‘Comparison to Fishcount’ sheet in the Open Phil spreadsheet. I think that Open Phil estimates are likely to be more accurate because they are more detailed. E.g., Open Phil accounts for the fact that the same species of fish are farmed until they reach a different age and weight in different countries. Furthermore, Open Phil made their estimate after considering the evidence presented by Fishcount and deciding that some aspects of their estimate could be improved.

From figure 5 in FAO (2018a), we can see that finfish aquaculture production in tonnes has been growing at an annual rate of 5% between 2012 and 2016. In the appendix, Cai and Leung (2017) extrapolate this trend and assume that the annual growth of global finfish aquaculture between the mid-2010s and early 2020s will be 4.81%. Hence, even though OpenPhil’s estimates are based on relatively recent data from 2016, we should expect farmed fish numbers to be even higher now. If we assume that farmed fish numbers are also growing also at 4.81% per year, we can extrapolate that in 2020 humans will slaughter 92.1B ✕ (1.0481)^4 = 111B farmed fish and that there are 85.2B ✕ (1.0481)^4 = 103B farmed fish alive at any time in 2020.

According to the Open Phil spreadsheet, China has about 52% of the world’s farmed fish alive at any time. It is followed by Indonesia (~10%), India (~10%), Bangladesh (~5%), Egypt (~3.4%), Vietnam (~2.7%), and Myanmar (~2.6%).

Note that there is a lot of uncertainty about all these estimates. Also note that all these numbers exclude shellfish. Fishcount estimates that in 2017 humans killed 43B–75B farmed crayfish, crabs and lobsters, and 210B–530B farmed shrimps and prawns.

Pre-slaughter mortality

Based on OpenPhil’s spreadsheet, I estimate that roughly 19B farmed fish die before the intended slaughter age (but after they are transferred from hatcheries) worldwide. However, there is some reason to suspect that this number could be much higher. In the appendix of Šimčikas (2019b), I present some sources that claim that 600B–700B of fish fry per year were produced in China in the early 2000s. I’m unsure whether to trust these sources because the claims seem very surprising, as numbers are much bigger than I’d expect.^[9] Also, these numbers may be too outdated to be relevant. Nevertheless, they weakly suggest that either mortality rates in fish farms are higher, or OpenPhil and Fishcount underestimate the number of slaughtered farmed fish. It’s also possible that some of these fish fry are bred to be released into the wild or for other reasons.

Note that the 19B figure and Open Phil estimates don’t account for the mortality of very young fish in hatcheries. Similarly, sources I cite in the appendix of Šimčikas (2019b) seem to talk about how many fish fry are produced by hatcheries. Since many fish die in hatcheries, the total number of hatched fish is even higher.

Finally, note that mortality rates seem to be higher in young fish and much lower as fish approach slaughter. Hence, the impact that the pre-slaughter mortality has on the number of farmed fish alive at any time is smaller than it would appear at first glance.

Fish bred for stocking

In Šimčikas (2019b), I estimated that 35B–150B fish are raised in captivity to be released into the wild every year, mostly to increase the catch in commercial and recreational fisheries. I am very uncertain about the mean age at the time of the release of these animals, but it seems to be somewhere between 8 days and 3 months. It follows^[10] that there should be 0.8B–50B fish being raised in captivity for the purpose of stocking at any time. This excludes fish who die in hatcheries before the release. Since many of these fish are released when they are juveniles and mortality during the early stages is high, this could significantly increase the number of fish being raised in captivity at any time. Consequently, I subjectively increase the estimate from 0.8B–50B to 0.8B–65B. As I explain in Šimčikas (2019b), I think that the number of fish stocked worldwide is more likely to be increasing than decreasing, but I am uncertain. Note that these estimates exclude shellfish who are also stocked in billions.

Fish bred for stocking may suffer in farms, during transportation and release. They also often struggle and starve after the release due to a lack of survival skills.

For a more in-depth overview of this practice, see Šimčikas (2019b).

Fish farmed to be used as bait by recreational fishers (baitfish)

In this context, baitfish are small fish who are farmed and then sold to recreational fishers, who impale them on a hook and use them as live bait to catch bigger fish. Farmed baitfish suffer not only during farming and when used as bait, but also when transported and kept by wholesalers, retailers, and fishers.

I covered the topic of baitfish in more depth in Šimčikas (2018a). Since I wrote the article, a 2018 U.S. aquaculture census was released. According to the table 4 of the census, 1.2B baitfish were sold in the U.S. in 2018. Similarly, according to the the U.S. 2013 aquaculture census, 1.17B farmed baitfish were sold in the U.S. in 2013 which suggests that the industry is currently neither growing nor shrinking (contrary to my claims in Šimčikas (2018a)).

Some sources suggest that the number of baitfish produced in the U.S. is much bigger than 1.2B. For example:

• In this 2014 video by Arkansas Farm Bureau, a vice-president of the largest baitfish hatchery claims that every year they produce 1.3B golden shiners alone and that this number doesn’t include goldfish and fathead minnows. According to the censuses mentioned above, there are around 0.5B golden shiners sold annually in the whole country.
• Stone et al. (1997) claim that in 1995 Arkansas produced 6B baitfish, utilizing 12,000 hectares of production ponds. The article claims that these figures were “[c]ompiled by individuals from Arkansas aquaculture industry and government aquaculture specialists.” According to table 16 in the 2018 U.S. aquaculture census, there were nearly 10,000 hectares used to produce baitfish in the U.S. in 2018. Based on this, it could be extrapolated that 10,000 ✕ 6B / 12,000 = 5B baitfish were produced in the U.S. in 2018. While I’m unsure if this extrapolation is appropriate, I think it does suggest that the number of baitfish produced could be significantly higher than 1.2B.

I think the most likely explanation of the discrepancy is that the two sources above write about how many baitfish are produced while the censuses report how many baitfish are sold. Stone (2003) claims that “in most years many more pounds of [bait]fish are raised than can be sold.”

In Šimčikas (2018a), I wrote that “most farmed baitfish are sold when they are about 1 year old”. This suggests that the number of farmed baitfish alive at any time is similar to the number of baitfish slaughtered annually, which seems to be somewhere between 1B and 7B.

Note that all of these numbers are for the U.S. only. Within the U.S., most of the baitfish seem to be produced in Arkansas (see table 16 in the 2018 U.S. aquaculture census). It seems that baitfish are not farmed at a large scale in most other countries. Ventura et al. (2017) show that baitfish are also farmed for recreational fishing in Brazil, but I haven’t found what is the scale of this production. In Canada, Australia, and probably some other countries, some fish are sold to be used as bait (see Kerr (2012), PIRSA (2018)). However, I haven’t seen evidence of baitfish being farmed in these countries, and it seems that in Canada they are wild-caught.

Minor update (March, 2022): slide 22 in this presentation has the following text: "There is no way to get an estimate of baitfish production in the MRBP

• Much of the fathead minnow production in ND, SD, MN, WI, and AR is sold as feeder fish
• Most goldfish raised in AR for feeder fish for aquarium industry
• No industry representatives thought USDA Aquaculture Census was accurate:
  • 2013 Census -- 12,891 acres of baitfish production in AR
  • AR baitfish growers estimate 20,000 acres in baitfish production"

Wild-caught fish

According to Fishcount estimates, the average number of wild-caught fish each year for 2007–2016 is 790B–2,300B. This estimate is based on FAO data. Page 93 in FAO’s SOFIA 2018 report claims that “it is recognized that the FAO capture database does not include all fish caught in the wild, as it omits the portion of the catch that is discarded at sea and catches from illegal, unreported or unregulated (IUU) fisheries.” Pauly and Zeller (2016) estimate that because of this issue, global catches between 1950 and 2010 were roughly 50% higher than data reported to FAO suggest.

While wild-fish spend most of their life in the wild, there is a period between being caught and dying that they spend in human captivity. There are many welfare issues during this period and they are summarized in Mood (2010). It can be useful to estimate how many fish are suffering from the issues described in Mood (2010) at any time and compare it with other animal problems. In subsections below, I attempt to make some such crude estimates.

Anchovies caught by purse seiners suffering due to overcrowding

According to Fishcount estimates, the species that are caught in the highest numbers are anchovies: 295B–908B per year (17%–65% of all wild-caught fish). Based on FAO descriptions, I estimated that 174B–880B of them are caught by purse seiners. To account for illegal, unreported or unregulated fisheries, I increase the upper bound by 50% to 1,312B. Mood (2010) claims that the duration of the most stressful period of purse seining is when nets are tightened and fish can not school. During this time, they experience stress due to overcrowding, injury due to collisions with the net and other fish. Mood (2010) cites Marçalo et al. (2006) to claim that this period lasts about an hour. If we assume that it’s 0.75–1.25 hours on average, we can estimate that 15M–187M anchovies are in tightened purse seine nets at any point in time on average. Note that this estimate is only for anchovies. Other fish species that are caught with purse seiners include sardines, mackerel, herring, and tuna. The estimate also excludes fish caught by other fishing methods and possible suffering of anchovies during other parts of purse seining.

Chilean jack mackerel caught by a purse seiner (source)

Fish suffocating after landing at any time

Mood (2010) claims that:

Most commercially-caught wild fish that are alive when landed are not slaughtered but die either from being left to suffocate in air or by a combination of suffocation and live gutting. Sometimes fish are put onto ice as they suffocate, or into iced water, which may both increase and prolong their suffering.

According to a Dutch study, during observation of fisheries at sea, the majority of most fish species caught were still alive and conscious when landed. The time taken to lose consciousness was measured for several species of fish (herring, cod, whiting, sole, dab, and plaice). Those left to asphyxiate took 55–250 minutes to become insensible. Those who were gutted first remained sensible for 25–65 minutes.

Fish suffering during suffocation seems to be intense. In most cases, violent attempts to escape are made and a maximal stress response is initiated (Robb and Kesti (2002)).

The cited dutch study is Van de Vis and Kestin (1996), but I couldn’t access it. According to Fishcount, there are 30B–68B herring, cod, whiting, sole, dab, and plaice caught annually.^[11] To account for illegal, unreported or unregulated fisheries, I increase the upper bound by 50% to 102B. If we assume that all of these species suffer from asphyxiation for 25–250 minutes when they are out of the water and 50%–100% of these fish suffer from asphyxiation before death, we get that on average 0.7M–49M herring, cod, whiting, sole, dab, and plaice are suffocating in air after being landed at any time.^[12] I am very unsure about this estimate because I have a very limited understanding of fish biology and commercial fishing. The estimate is based only on my interpretation of the cited sources.

The combined number of all wild-caught fish suffocating in the air at any time could be much higher. Time taken to suffocate for fish species can be very different:

• This video claims that “anchovies die immediately when they are out of water.” However, the video is not about fish welfare and may ignore the fact that it takes some number of minutes for them to suffocate if it’s not economically important.

• According to Table 12-3 in EFSA (2004), time to loss of brain function due to asphyxiation in the air is about 5.5 minutes for Gilthead sea bream and 2–3 minutes for rainbow trout. Note that these times are for specific temperatures. If rainbow trout are iced, then they lose brain function in about 10 minutes (Table 12-4).

• Fishcount claims that “there is anecdotal evidence of flatfish landed by a trawl surviving ten hours out of water.”

I'm unsure if any of the cited sources assume that fish are alive just because they continue to move. This could be a mistake because fish can move after their death. EFSA (2004) claims that "because carcass movement ceases after consciousness is lost, this criterion cannot be used as an indicator of death."

Other

I made the estimates above only because I was able to find some relevant numbers, not because I believe these to be the most important groups of animals suffering in captivity due to fishing. Other groups of wild-caught fish in captivity include:

• Fish trapped in nets. Mood (2010) describes how fish get trapped in nets, are injured in the process and then may struggle in nets for many hours or even days until the net is retrieved.
• Longline fishing is a commercial fishing method that uses hundreds or even thousands of baited hooks hanging from a single line, which may be 50–100 km long. Fish caught on long lines may stay hooked for hours or days until the gear is hauled up. During this time, they may be attacked by predators and parasites (Mood (2010)).
• Baitfish used in commercial fisheries. Mood (2010) claims that fish are sometimes used as live bait in various commercial fishing methods. It seems that all (or almost all) of these fish are wild-caught. According to Mood (2010), “these bait fish will have suffered fear and distress caused by capture and confinement, possibly for days or weeks, before they are impaled on hooks or scattered live amongst shoals of tuna.” I haven’t found any estimate of how many baitfish are used by commercial fishers. However, the numbers could be very significant. The last paragraph of Mood and Brooke (2019) very roughly estimates that 134B–324B fish are used for non-food purposes (other than fishmeal and fish oil) every year. According to FAO (2018b), this includes using fish “for feed and bait, for ornamental purposes, withdrawals from markets and any other non-food use of fish production (e.g. fertilizers, medical uses).” However, I don’t know what proportion of the estimated 134B–324B fish are used as live bait or feed in commercial fishing. Note that these fish are not included in my estimate of the number of baitfish farmed for recreational fishers.

Farmed feeder fish

Feeder fish are fish that are sold in order to be eaten (sometimes alive) by other captive animals, like reptiles, bigger fish, and sharks. Woempner (2012) describes cruel conditions in which feeder fish are kept in some U.S. pet stores.

Arkansas Farm Bureau (2019) contains a video about a U.S. farm which reportedly raises around 175M goldfish each year. In the video, it is claimed that the majority of these fish are fed to aquarium fish. This suggests that feeder fish numbers can be significant.

I’m unsure how prevalent is the practice of using feeder fish to feed aquarium fish around the world. Clarke (2006) claims that the use of feeder fish is relatively common in the U.S., but virtually unheard of in the UK.

Note that in this section I exclude wild-caught fish used to feed other animals, which are much more numerous. Mood and Brooke (2019) estimate that 460B–1,100B fish are reduced to fishmeal and fish oil every year (the estimate is based on 2007-2016 FAO data). Most of this fishmeal and fish oil is then fed to farmed animals, mostly farmed fish and crustaceans. Furthermore, some wild-caught fish are used as feed without being reduced to fishmeal and fish oil.

Cleaner fish

Cleaner fish is a term used to refer to species that are deployed in farmed salmon cages to pick off and eat the sea lice from passing fish. The predominant species used are Ballan wrasse and lumpfish (Marine Conservation Society (2018)). According to Powell et. al. (2017), there were well over 30M lumpfish juveniles deployed in 2016. It also claims that to meet global industry needs, lumpfish production needs to increase to reach 50M fish annually by 2020, 10M of which required in the UK. According to Norwegian Directorate of Fisheries (2018), in 2018 in Norway there were 2M farmed wrasse and 29M farmed lumpfish sold as cleaner fish. This excludes wild cleaner fish. In total, 49M cleaner fish were used in Norway in 2018. According to Fishcount statistics, about half of the farmed salmon is produced in Norway. Based on that and other sources, my impression is that Norway accounts for the majority of used cleaner fish and that the number of cleaner fish deployed around the world does not exceed 90M. Cleaner fish welfare problems are described in OneKind (2018).

Vaughan, Grutter and Hutson (2018) claim that cleaner shrimps could be used in fish farming of various species in the future. This could significantly increase the number of animals involved in fish farming.

Eel trafficking

There is a high demand for eels as food in Japan and China. This demand can no longer be met by wild-caught eel due to decreasing catches. It is also not known how to grow eel through their entire lifecycle in captivity (The Economist (2019)). Instead, millions of baby eels are caught from the wild, illegally trafficked from Europe to Asia where they are grown in farms and slaughtered. According to Galey and Billing (2018), eels are smuggled in vans and lorries, put into suitcases, and then flown by commercial airliners. In addition to animal suffering that this may involve, the process is also contributing to the decline of eel numbers in the wild.

According to Europool (2018), “it is believed that, for the current season, 100 tonnes of eels have been smuggled from EU to China”. According to The Economist (2019) and Galey and Billing (2018), 100 tonnes is about 300M–350M eels. However, Sustainable Eel Group (2018) claims that the quantity of eels smuggled annually is somewhere in the middle of the range of 8 tonnes (about 28M eels) and 100 tonnes. They also claim that this quantity “varies enormously from year to year.” Note that none of these eels seem to be accounted for in the FAO statistics that farmed fish estimates in this article are based on.

In addition to eels trafficked from Europe, Tjandraningsih (2013) claims that eels are also trafficked from Indonesia. I’m unsure if there are other animal species that are trafficked in such huge numbers. Galey and Billing (2018) and The Economist (2019) claim that eel is the most trafficked animal in the world.

Sturgeons farmed for caviar

Caviar is made from fish eggs, mainly sturgeon eggs. EUMOFA (2018) claims that “from a global point of view, production of sturgeon, and especially caviar, is very small.” According to Bronzi et al. (2019), the global farmed caviar production has progressively increased over the last 15 years, with production in 2017 amounting to approximately 364 tonnes. Romeo (2019) claims that one Italian caviar farm houses 300,000 sturgeons. The article claims that this and another Italian caviar farm together produce 25 tonnes of caviar. From these and other figures, I extrapolate^[13] that there are around 10.75M sturgeons farmed for caviar in the world at any time. Ehret (2019) claims that one Chinese farm keeps 200,000 sturgeons and produced 86 tonnes of caviar last year. From this we can extrapolate that 200,000 ✕ 364 tonnes / 86 tonnes = 846,511 sturgeons are used for caviar production globally. Based on these extrapolations, I think it’s that the number of sturgeons farmed for caviar in the world at any time is most likely to be somewhere between 1M and 15M. My impression is that the number of all other species of fish farmed for their eggs is significantly lower.

FAOSTAT land animal numbers

The most widely used statistics about farmed land animals come from the Food and Agriculture Organization of the United Nations website FAOSTAT. It contains estimates of the number of animals slaughtered and alive at any time in each country and for each year. These statistics are collected by countries and aggregate official, semi-official, and estimated data. To my knowledge, these are also the best available statistics on the topic. However, there are some inconsistencies in them that suggest accuracy issues (see Šimčikas (2019a)).

In the table below, I combined FAOSTAT live animals and livestock primary numbers for 2018 for all countries. “Main uses” column is filled by me based on brief web searches.

The numbers in the table may not add up due to rounding. For more precise numbers, see this spreadsheet or the FAOSTAT website.

These animals are used for various purposes. FAO claims that “the data on livestock numbers are intended to cover all domestic animals irrespective of their age and the place or purpose of their breeding.” However, these stats seem to exclude quail, animals used for research, minks farmed for fur, rodents farmed for pet snake food, etc. I’m also unsure if the FAOSTAT numbers include all the animals kept by subsistence and small-scale farmers (e.g., chickens kept in backyards).

It is difficult to determine how many animals are used for what purpose. This task is complicated by the fact that the same animal is often used for multiple purposes. E.g., the same cow may be used for milk, working, meat, and leather. Similarly, the same sheep may be used for wool, meat, and milk, although most sheep breeds are specialized for one or two of these purposes.

Live animal trade

Live animals are routinely transported by road, rail, sea, or air across different countries and continents. According to CIWF, transported animals suffer from overcrowding, exhaustion, dehydration, extreme temperatures, and other problems. According to RSPCA, they also suffer from injuries due to inappropriate handling, inappropriate vehicles, mental distress due to unusual and potentially frightening sights, movements, noises, smells, unfamiliar animals and stockpersons. Furthermore, live animal trade can spread diseases across the globe.

In this page, FAOSTAT provides estimates of numbers of animals exported/imported alive by each country. In the table below, I present combined live import and export data for all countries in 2017:

Sources and reasons for import-export inconsistencies are explained by FAO here. Note that the numbers of animals traded live are rising. Also note that some animals who are not traded between countries can still be live-transported long distances within a country. For example, CIWF claims that cattle are transported across India and farm animals are transported for thousands of miles within Canada. Finally, note that these numbers exclude live-traded fish, pets, and other animals.

Chickens

Chickens in the egg industry

According to FAOSTAT data, there were 7.5B egg-laying hens in the world in 2018. However, I noticed inconsistencies in the FAOSTAT data, which led me to believe that this number is inaccurate. For example, FAO statistics for the UK seem to include not only layers but also pullets (hens who are too young to lay eggs) and roosters (who are used for breeding hens). FAO statistics for the U.S. include layers, but not pullets or roosters (see Šimčikas (2019a)). If all countries reported hen numbers in the way U.S. did, the total number of chickens involved in egg production globally would increase from 7.5B to roughly 10.3B.^[14] Since it seems that different countries reported the data in different ways, I think that most likely, the real number is between 7.5B and 10.3B.

Note that this includes 390M–670M mothers and fathers of meat chicken (estimated in one of the sections below). If we exclude them, we get that there are 6.8B–9.9B chickens involved in the production of eggs for consumption.

According to FAOSTAT, about 39.1% of the worlds egg-laying hens (including mothers and fathers of meat chicken) are in China, 25.8% in other Asian countries, 10.8% in Europe, 7.7% in South America, 6.9% in Africa, 5.7% in North America, and 3.3% in Central America.

Chickens bred for meat (broilers)

According to FAOSTAT, there were 23.7B chickens alive in captivity in 2018. Also, in the section above, I explained that there are 7.5B–10.3B chickens used in the egg-laying industry. It would follow that there are 13.4B–16.2B chickens raised for meat at any time. Perhaps even more because some chickens are raised for both meat and eggs. However, according to a rough estimate in an Open Phil spreadsheet (Broilers (2017) tab), there are 9.55B meat chickens in the world. I’m unsure which estimate is more accurate. Hence, I think that the number of meat chickens in the world is in the range of 9.5B–16.2B.

Update 2022-09-05: I now firmly believe that the number of chickens in the world is much closer to 9.5B and could be even lower. It turns out there is an issue with U.S. chicken stocks data in FAOSTAT. Because of the mistake, the stats currently show that there are 9B chickens in the U.S. when in reality the number is closer to 2B (see this table). The numbers FAOSTAT were using come from the “Broilers Produced” table in this document but the table shows how many meat chickens were slaughtered (or perhaps hatched) in a given year, not the number alive at any time. I’ve discussed this issue with FAOSTAT and they agreed that this is a mistake. Fixing this error would bring down the number of chickens alive at any time from 23.7B to about 16.7B. If we calculate the number of broilers alive at any time using FAOSTAT numbers by subtracting the number of laying hens from the number of chickens, we now get 16.7B-7.5B=9.2B, which is close to the OpenPhil’s estimate of 9.5B. Hence, I now use OpenPhil's estimate of 9.5B. The lower bound would be 16.7B-10.3B=6.4B (see the estimate in the paragraph above).

Meat chicken mothers and fathers (broiler breeders)

The estimate of meat chickens above excludes their mothers. They are hens who lay eggs that hatch into meat chickens. These hens might be suffering even more than meat chickens because they are kept hungry all the time to avoid gaining excessive weight (see Sethu (2014)).

I haven’t found a dependable estimate of how many meat chicken mothers there are in the world. I tried to extrapolate it based on statistics for various years and regions (U.S., UK, EU, South Africa, Brazil, Pakistan). According to most of my extrapolations, there are 350M–600M meat chicken mothers in the world. All extrapolations can be seen in this spreadsheet. They involved some simplifications^[15], but I think that the result should be roughly correct.

I also estimate^[16] that there are roughly 40M–70M meat chicken fathers in the world. I don’t know if they face similar welfare issues to mothers.

Culled male chicks

In the egg industry, male chicks are usually culled (slaughtered) at a very young age (e.g., one day) because they can not lay eggs and are less suitable for meat production than meat chicken breeds. It seems that they are excluded from the FAOSTAT slaughter totals.

CIWF (2015) claims that 5B male chicks are culled per year. Fleming (2016) claims that it’s 3.2B. WATTAgNet (2018) claims that it’s 6B. Krautwald-Junghanns et al. (2018) and Vogel (2019) claim that it’s 7B. None of these sources explain how they attained these figures, and I don’t know if any of the authors made detailed estimations. Note that the number of egg-laying hens alive at any time has been increasing, which may explain why some earlier sources claim that the number is lower.

Other birds

Quail

Quail are small birds who are farmed for their meat and eggs. CIWF claims that the vast majority of quail are farmed intensively in battery cages or overcrowded barns.

Quail farming. A photo from Tasnim News Agency.

I haven’t found any reliable estimates of the number of quail farmed in the world. Chang et al. (2007) and Xu et al. (2003) claim that there are about 1B quail around the world, but the source for the claims is unclear. According to Table 1 in Minvielle (2004), there are 169M Japanese quail slaughtered for meat and almost 11B quail eggs produced (presumably per year). However, the paper claims that figures lack precision. Furthermore, the paper uses some sources that date back to 1991.^[17]

According to da Cunha (2009), by far the biggest quail producer is China. The article claims there were about 80M quail housed exclusively for meat and 270M–300M quail kept for egg production at the time of writing the article in 2009. From this, the article estimates that 1.3B–1.7B quail are slaughtered for meat in China every year (including 315M–350M egg-layers slaughtered after their productive period). The numbers now could be even higher since the article claims that there were perspectives for an increase in the quail egg production.

Other countries with significant quail production include:

• Brazil. According to figure 1 in Bertechini (2012), around 18M quail were housed in Brazil in 2012. The article predicts that in 2020, 36M quail will be housed in the country. It seems that most of these quail are raised primarily for eggs.
• U.S. According to table 30 in the 2018 Census of Agriculture, in 2017, there were 7.4M quail farmed in the U.S. at any time and about 23M quail were “sold”.
• Spain. According to da Cunha (2009), in 2004, Spain produced an estimated 9,300 tonnes of quail meat. In estimations for China, da Cunha (2009) assumes an average carcass yield of 140g. If this is roughly true for Spain’s production as well, it follows that about 66M quail were slaughtered in Spain in 2004. Assuming slaughter age of 5 weeks, that’s about 6M quail raised for meat at any time.
• France. According to official statistics, 38M quail were slaughtered for meat in 2008. Assuming slaughter age of 5 weeks, that’s about 3.6M quail raised for meat at any time. The source also claims that 83M quail eggs were produced in 2008. Assuming 230 eggs per year per bird, there were roughly 0.36M laying quail in the country.
• Italy. According to da Cunha (2009), 20M–28.5M quail are slaughtered in Italy every year. Assuming slaughter age of 5 weeks, that’s about 1.9M–2.7M quail raised for meat at any time.

If we add up these numbers,^[18] we get that these countries slaughter about 200M quail annually and house very roughly 55M quail at any time. If we add this to the estimates for China, we get that there are roughly 420M quail housed at any time, and 1.5B–1.9B quail slaughtered annually.

These estimates seem to exclude breeders (quail mothers and fathers) and hens who are too young to lay eggs. Furthermore, they exclude quail raised in other countries. According to Bertechini (2012), the only major quail producer that the list above excludes is Japan.

If I account for breeders, mortality, and other countries, my best guess is that there are about 400M–550M quail farmed in the world, and that 1.5B–2.5B quail are slaughtered annually. However, these estimates are mostly based on old statistics, and I’m unsure how dependable the sources are.

I don’t understand why there is no category for quail in FAOSTAT. Perhaps some of the birds categorized as “Bird, meat, not specified” and “Egg, other bird” are quail. However, it seems that there are many more quail than birds in these categories. FAO claim that “[c]ertain other countries give a single figure for all poultry; data for these countries are shown under “Chickens”.” Hence, it’s also possible that some of the chickens in the FAO statistics are actually quail.

Foie gras

Foie gras is a specialty food product made of the liver of a duck or goose. The production of foie gras usually involves fattening birds by force-feeding them with a tube. Some animal advocates focus on fighting against this practice due to its cruelty.

According to Willsher (2012), France is responsible for 75% of the world’s foie gras production and slaughters around 38M ducks and geese for this purpose every year. It follows that around 38M / 0.75 = 50.7M ducks and geese were slaughtered for foie gras every year globally. However, the source of Willsher (2012) numbers is unclear and could be outdated. Note that, in some countries (but not France), foie gras could be produced using natural feeding.

Euro Foie Gras claims that in 2018, the EU produced approximately 22,600 tonnes of duck foie gras and 1,900 tonnes of goose foie gras and that this is about 90% of the world’s production. Nistor et al. (2005) claims that duck foie gras weighs 350 g to 600 g on average and goose foie gras weighs 600 g to 800 g on average. Using this information, I roughly estimated that 45M–64M ducks and geese were slaughtered for foie gras globally in 2018.

According to an archived factsheet from Viva!, “Ducks are typically slaughtered at 100 days and geese at 112 days.” Similar slaughter ages can be deduced from other sources. It follows that there are roughly 11M–19M birds alive at any time for foie gras production. This estimation excludes breeders and birds who die before slaughter.

Another relevant statistic from the Viva! spreadsheet is that ducks are force-fed twice a day for 12.5 days and geese three times a day for around 17 days. Similar figures are given by other sources. If we assume that 92%–100% of the 45M–64M birds are force-fed, we get that roughly 1.4M–2.3M ducks and geese are in the force-feeding period at any point in time.

All the estimations can be found in this Guesstimate model. Note that even though I use Guesstimate, my results are not a 90% subjective confidence intervals. I’m unsure how reliable the information in used sources is.

Down

Waterfowl (mainly ducks and geese) have a layer of down feathers closest to the skin, which are sought after for use in bedding and outdoor clothing. I was unable to estimate how many birds were plucked for their down.^[19] However, according to FAOSTAT, in 2017, there were estimated 371M geese and guinea fowl and 1.2B ducks alive in captivity at any given time in the world. A large proportion of them are reared for meat production, with down and feathers being a valuable byproduct, as illustrated by the industry sizes. According to IndexBox (2019), the global duck and goose meat market revenue amounted to $19B in 2018. Comparatively, according to Profshare (2017), the down feather market was valued at $5.9B in 2017, and is expected to reach $10.25B by the end of 2025.

Some geese and ducks are plucked for their down while they are still alive. PETA claims this involves substantial pain and distress for birds, who have feathers ripped from their skin. The proportion of down that comes from live-plucked birds is unclear. Kozak, Gara and Kawada (2010), claim that only 1–2% of total goose feathers and down is sourced through live-plucking. However, they don’t provide any explanation about how they arrived at this estimate. As the RSPCA acknowledges, statistics on the extent of live-plucking are lacking. Hendriksz (2016) illustrates that plucking often occurs ‘in secret’, despite regulations.

Note that buying down can cause suffering even if its production doesn’t include live-plucking. It supports meat and foie gras industries as many farmers who raise birds for food make extra revenue by selling their feathers. Furthermore, PETA claims that “many of these birds are improperly stunned, which means that they are still conscious when their throats are cut and they are dumped into the scalding-hot water of the defeathering tank.”

Swiftlets

The swiftlet farming industry involves the harvesting of edible birds nests, which swiftlets construct from their saliva. The nests are then sold and eaten in an expensive delicacy, birds nest soup. They are also increasingly used within the beauty industry and elsewhere. Demand is highest in Asia, mainly China (Chua and Zukefli (2016)). My impression is that swiftlets do not suffer as much in comparison to other farmed animals.^[20] However, this industry seems to be rapidly growing, and I don’t know if farming practices will remain as they are.

Mammals

Working animals

The FAOSTAT statistics include at least some of the working animals that are used for tasks like pulling carts, plowing, transporting materials and people, and other purposes.^[21] Statistics usually do not distinguish for what purpose animals are used. Hence, it is very difficult to estimate the number of working animals in the world. Starkey (2010) claims:

There are few authoritative estimates of work animals: only some governments record their numbers. National herd figures from FAOSTAT are good estimates for mules and donkeys which are kept for work. They are less reliable for horses and camels that may be kept for other purposes. Most cattle and buffaloes are maintained for meat or milk and these species require survey data to gauge working uses. Unsubstantiated estimates prepared around 1980 suggested 300-400 million working animals in the world. Since then, numbers in Africa have increased with significant decreases in some Asian countries, notably China and Bangladesh. Current world use may be 200-250 million.

Other unsubstantiated estimates I found also vary between 200M and 300M animals used for work, with one 1999 estimate claiming that it’s nearly 600M.^[22] Note that in addition to working, these same animals may be used for milk, meat, wool, hair, off-springs, hides, horns, hooves, etc.

See Alves (2018) for a general overview of working animals. It claims that despite the advances of mechanization, the importance of working animals as a source of power is likely to continue in the foreseeable future.

There are many serious concerns about the welfare of working animals, especially in developing countries. They suffer from overwork, poor nutrition, inadequate basic health care, bad treatment by the owners, lack of water, inappropriate equipment, cruel practices, etc. (see Rahman and Kahn (2014), Yee (2016), worldanimal.net overview)

Animals used for transport in Nepal. A photo by Gunjan Raj Giri.

Purposes

Here is an incomplete list of categories of working animals:

• Agriculture (e.g., plowing, threshing grain by trampling, powering machines that grind grain or supply irrigation)
• Transport/pack animals
• Logging (e.g. timber elephants and oxen)
• Animals in law enforcement (police horses, police dogs)
• Assistance/service animals (assist disabled people, e.g. guide dog)
• Guard animals (e.g., guard dog, livestock guardian dog, guard llama)
• Search and rescue animals (search and rescue dog, search and rescue horse)
• Herding animals (herding dog, Judas goat)
• Hunting dogs
• Military animals
• Animals used to assist in therapy
• Fish used for pedicures
• Farm cats
• Animal actors

Worldanimal.net claims that “the majority of working animals are involved in transport and agriculture.” Animals used for work include oxen, water buffaloes, yaks, horses, asses, camels, mules, dogs, elephants, reindeer, rats, and others.

Fur farming

Lung and Lin (2019) provides estimates of how many minks, foxes, and raccoon dogs are farmed in China, EU, USA, and Canada in 2016:

• 71M minks (26.2M in China, 39M in Europe, 3.5M in the U.S. and 2.1M in Canada)
• 15M foxes (12.6M in China, 2.7M in Europe)
• 15M raccoon dogs (almost all in China)

In total, that’s about 100M. My impression is that this covers most of the animals farmed for fur. However, this number excludes some animal species and countries. It also seems to exclude trapped animals. TruthAboutFur.com (a pro-fur website) claims that worldwide, about 85% of the furs produced come from farmed animals. The rest comes from trapped animals. The website also claims that farmed animals are “primarily mink and fox, but also chinchilla, Finn raccoon (Asiatic raccoon), sable, Rex rabbit, Karakul sheep and other species.”

Open Phil (2019) combined information from multiple sources and estimated that about 60M mink were farmed globally in 2018, down from more than 100M in 2015. The article also estimates that “about 45M animals are suffering on fur farms at any time.” However, they do not provide the details of their estimate.

Hansen (2017) claims that the 2015 fur production is in the order of 85M mink furs and 95M furs in total.

It seems that fur animals are mostly fed various meat by-products (e.g., see this and this).

Rabbits

Many websites claim that over one billion animals are killed for fur every year (e.g. 1, 2, 3). PETA’s page about fur cites Lebas et al. (1997) as the source for the same claim. Lebas et al. (1997) have the following excerpt, which might be the base for all of these claims:

“Mink, which tops the list of species bred essentially for its fur, supplies a world total of about 25 million to 35 million pelts a year whereas rabbit pelts are estimated at one billion.”

However, in the same section, Lebas et al. (1997) call rabbit skin a by-product of meat and claim that most rabbit skins are thrown away. Hence, it seems that the claim that PETA and other websites make is inaccurate. According to FAOSTAT, there were 564M rabbits slaughtered for meat in 1997, which makes the one billion figure from Lebas et al. (1997) surprising. In 2018 there were 922M rabbits slaughtered.

Open Philanthropy Project (2019) claims that rabbits are farmed mostly for their meat, but some are farmed exclusively for their fur. Lung and Lin (2019) claims that:

It is estimated that tens of millions of rex rabbits are also used each year for their pelts, but because these rabbits are also used for their meat, it is difficult to separate data from the two industries and state which is the primary purpose of breeding. Taking published figures from 2011 to 2012 as an example, 130 million rex rabbits were reportedly bred and processed into fur in China.

Rodents farmed for pet snake food

In Šimčikas (2019c), I estimated that 160M–2.1B vertebrates are killed for pet snake food every year. Most of the vertebrates seem to be mice that are usually farmed in bad conditions. These mice are killed when they are anywhere between 48 hours and more than 9 months old. Most seem to be slaughtered when they are 3–4 weeks old, although I’m uncertain. Assuming that the average farmed rodent lifespan is between 1 week and 2 months, we can estimate that there are 3M–350M rodents farmed for pet snake food at any one time.

Farming of feeder rodents seems to involve considerable suffering because they are often kept in cramped and possibly unsanitary conditions, lack shelters, daylight, and activities. See Šimčikas (2019c) for a general overview of the issue.

Rodents bred for human consumption

According to Gruber (2016), rats are “a regular staple” in many countries in South East Asia. It also claims that rodents are eaten in Africa, South and Central America. It seems that many of the rodents eaten are caught from the wild rather than farmed (see Gruber (2016), Dell’Amore (2019)). However, Gruber (2016) also claims that “some experts suggest that farming and eating rodents could be one solution for alleviating the world’s hunger and malnutrition problems.”

According to FAOSTAT, in 2018, there were 71.3M rodents slaughtered in the world, and there 19.2M farmed rodents alive at any time,^[23] all in Peru and Bolivia. These stats seem to be somewhat incomplete because they exclude Africa. Jori et al. (2005) claims that rodent farming is “slowly developing in some parts of Africa” but “rodent farming projects are not the panacea and many problems still need to be solved to reach a large scale production”. Maass et al. (2014) claims that more than 2M cavies are already kept in DRC and suggest that cavy culture in DRC is likely to become more widespread. Maass (2019) claims that guinea pigs are farmed in many other African countries (Benin, Cameroon, Côte d’Ivoire, Ghana, Kenya, Nigeria, Tanzania, and Togo). It also claims that they are predominantly kept in houses or kitchens and are not included in most national statistics.

Edit April 27th, 2020: Thomson (2020) claims that Chinese farmers were rearing about 25M bamboo rats when the government launched a ban on the trading and consumption of wild animals in the wake of the COVID-19 outbreak. According to Thomson (2020), "the possibility of bamboo rats being allowed back on the dinner plate would be slim." The ban probably also impacts some other groups of animals that are described in this article. However, Waldhorn (2020) claims that "it is known that law enforcement, especially regarding animals, can be a problem in the region. Additionally, due to the size of the market, if a ban is not adequately managed, it can lead to an explosion of a black market for animals. "

Dogs and cats killed for meat and fur

According to HSI, 30M dogs and 10M cats are killed annually for human consumption across Asia and that there are thousands of dog meat farms in South Korea. According to AnimalsAsia, 10M dogs and 4M cats, are slaughtered for meat in China. None of these estimates are substantiated.

ACTAsia for Animals (2017) claims that there are many dog farms in China and that cat breeding farms are less common. It also claims that dogs and cats (including family pets) are often taken from streets in order to be slaughtered. It’s also suspected that some slaughtered dogs come from overcrowded dog shelters.

Slaughtered dogs and cats are used for meat and fur. Internal dog organs are also used in traditional Chinese medicine (ACTAsia for Animals (2017)).

Puppy mills/farms

Puppy mills are defined as dog breeding operations in which the health of dogs is disregarded in order to maintain a low overhead and maximize profits.

• U.S. HSUS (2019) claims that estimated 2.4M puppies who originated from puppy mills are sold in the U.S. annually. About half of them were raised in USDA-licensed facilities. About 200,000 dogs were kept solely for breeding purposes in USDA-licensed facilities. HSUS website provides more information on the topic.
• UK. Naturewatch claims that “up to 400,000 farmed puppies are sold to the British public every year.” Elgot (2019) describes a recently-passed law that may help to decrease the scale of the problem in the country.

None of these sources fully explain how they arrived at these numbers. As I understand it, these are only estimates of dogs bred in bad conditions. The total number of dogs in breeding facilities is probably much higher. Hughes and Macdonald (2013) estimate that the global domestic dog population abundance is over 700M. It’s likely that a significant proportion of them originate from breeding operations.

It seems that puppy mills also exist in countries like China (Jones (2018)) and India (Block (2018)). Since dogs are used as pets around the world, I expect that puppy farms exist in many other countries as well.

Other pet mills

Similar to dogs, many other animals are sometimes bred in bad conditions to be sold as pets. Animals Australia page and petful.com article describe inhumane conditions in kitten mills. Schelling (2016) and HSUS (2019) describe cruel conditions in which rabbits and rodents are raised to be sold to pet stores. I haven’t tried to find the number of animals raised in these facilities.

Dog and cat shelters

According to the ASPCA, approximately 3.3M dogs and 3.2M cats enter U.S. pet shelters every year. After a brief search, I failed to find statistics for other countries or how many animals are alive in the U.S. pet shelters at any time.

Deer farming

According to the official New Zealand statistics, there were 851,000 farmed deer in the country in 2018. According to Table 32 in the 2017 U.S. Census of Agriculture, there were 212,449 deer in captivity in the U.S. in 2017. Vegetarian society claims that “4,612 farmed deer were slaughtered for their meat (venison) in the UK in 2010.”

Bullfighting

HSI claims that “every year, approximately 250,000 bulls are killed in bullfights.” The same claim is made by WAP. PETA also used to make the same claim but now PETA claims that “in 2018, at least 7,000 bulls were killed in official bullfights in Spain.” It also claims that “the number of bulls killed has been decreasing since 2007.” CAS International claims that “it is estimated that worldwide more than 180,000 bulls, cows and calves are abused and slain during bullfights and similar events every year.” Note that the number of animals used in bullfighting may be much bigger than the number killed. A lot of statistics on bullfighting in Spain and some other countries are analyzed in AVATMA (2018). It claims that the data on bullfighting is contradictory. My impression is that the number of animals killed in bullfights is much smaller than 250,000, but I’m not confident.

Horses kept for recreation, competition, and racing

There are numerous horse-related activities listed here. According to Ross (2019), in the U.S. alone, there are 3.1M used for recreation, 1.2M for competition, 1.2M for racing, and 1.5M used for other purposes. However, the article doesn’t provide a source for these numbers.

Thoroughbred horse racing

According to McManus, Albrecht and Graham (2012), in excess of 110,000 thoroughbred horses are born each year throughout the world. Only 5% to 10% ever see a racecourse according to The Horse Fund. Tens of thousands are slaughtered annually due to overbreeding (PETA), with others being used for purposes other than racing.

McManus, Albrecht and Graham (2012) claims that in 2009 there were 162,891 thoroughbred horse races held in 47 countries, with over 250,000 horses starting a race. This figure of 250,000 excludes females, foals or sires (males kept for breeding purposes); only racehorses, typically 1–2 years of age. Therefore, the actual figure for the number of thoroughbreds kept in captivity at any given time is likely to be multiple times higher. Ross (2019) claims that there are 1.1M thoroughbred horses in the U.S. alone.

Greyhound racing

According to GREY2K USA worldwide (2019), commercial greyhound racing exists in seven countries at nearly 150 tracks worldwide. The article claims that each year, the greyhound industry worldwide breeds at least 48,000 greyhound pups. According to the article, the greyhound racing industry has rapidly declined by over 70% over the last ten years, and this trend is expected to continue.

Bear farming

Bears are kept in captivity to harvest their bile, a digestive fluid produced which is used in traditional Chinese medicine. According to Black (2007), researchers believe that more than 12,000 bears were kept on farms in China, Vietnam, and South Korea in 2007. WAP claims that there are up to 20,000 bears farmed across Asia but doesn’t provide a source for the claim. Animals Asia (2019) describes cruel conditions in which bears are farmed.

Lion and tiger farming

According to World Animal Protection (2019), 12,000–17,000 lions and tigers are raised in harsh captive conditions to be used for traditional Asian medicine products. In some cases, they are also used for tourism experiences. Most big cat breeders are in China and South Africa. World Animal Protection (2014) claims that there are also 5,000 captive tigers in the U.S., presumably mostly used as a tourist attraction. Note that many animals may be killed to feed these carnivores.

Civet farming

According to worldanimal.net, approximately 3,000 civets are kept in primitive conditions on over 200 farms in Ethiopia. They are farmed for musk, which is used in perfumes by several perfumeries in France.

Civets are also kept in captivity to produce civet coffee. This coffee includes partially digested coffee cherries, eaten and defecated by the Asian palm civet. I haven’t seen any estimates of how many civets are kept in captivity for this purpose.

Mixed species

Animals used for research and research-related purposes

Taylor et al. (2008) conservatively estimated that in 2005 there were 58M vertebrates used in research worldwide and 57M used for research-related purposes. In total, that's 115M animals. In this context, research-related purposes are:

• killing animals only for tissue supply,
• using animals to maintain genetically modified breeding colonies,
• breeding animals for laboratory use but killing them without experimentation because they are surplus to requirements.

Knight (2008) analyzed the data of Taylor et al. (2008) and suggested that the figure should be 127M rather than 115M. Knight (2008) still considered the estimate to be conservative and far from precise. Lush Prize (2014) updated Taylor et al. (2008) and estimated that in 2012 the number of animals used in research (including research-related uses) was 118M.

Cruelty Free International claims that “animal experiments are sadly not in decline, and in many parts of the world are on the increase (e.g. China) or remain at the same level as they were in the 1980s or 1990s (e.g. the UK, Europe).” Faunalytics' summary of Cao (2018) claims that "each year, Chinese laboratories use 12-13 million animals in research". This is much more that Taylor et al. (2008) estimate for China which is 3M.

Update: Taylor & Alvarez (2020) estimated that 192.1M animals were used for scientific purposes in 2015.

U.S.

Taylor et al. (2008) roughly estimates that there are 17.3M animals used for research in the U.S. However, it also notes that the number could be much bigger. USDA (2000) describes a survey of 50 of 2,000 U.S. research institutions. Combined, these 50 institutions reported using 0.25M–1M rats, 0.4M–2M mice, and 0.13M–0.9M birds. From this, Taylor et al. (2008) extrapolates that there are 31–156M animals used for research-related purposes in the U.S. alone, and concludes that its 115M figure may be “a substantial underestimate”.

USDA (2000) also claims that it is estimated that more than 500M rats, mice, and birds are used in research, breeding, exhibition, and transport in the U.S. but doesn’t explain the estimate.^[24]

Goodman, Chandna, and Roe (2015) claim that the number of animals used for research in the U.S. has increased significantly between 1997 and 2012.

Animals dissected in classrooms

Estimates of animals used for research purposes don’t seem to include animals dissected in classrooms. National Anti-Vivisection Society claims that estimated 6M–12M animals of various species are either “purpose bred” or harvested from the wild for use as dissection specimens in the U.S. Similarly, PETA claims that in the U.S., estimated 20M animals are used for teaching exercises annually, and that about 10M of them are dissected in classrooms. Animals are also dissected in classrooms in the UK and probably in many other countries. Hence, worldwide numbers could be multiple times higher.

National Anti-Vivisection Society also claims that dissection teaches students that animal lives have little importance and that it is not needed for teaching because “numerous studies have reported that students who utilize humane alternatives to dissection score as well or better on performance tests than students who participate in dissection.”

Selling live food animals

In some parts of the world, all kinds of live animals are held alive in wet markets and butchered before the sale or sold alive to customers. The practice has recently received a lot of mainstream publicity because it is linked to outbreaks of new human viruses. In addition to increasing the risk of pandemics, the practice also seems bad from an animal welfare perspective. From pictures I’ve seen, it seems that these animals are usually kept in bad conditions. In addition, animals may also suffer when they are transported to markets and from markets to households. I think that fighting against the selling live animals for food could also help with the moral circle expansion because the practice could be making people in markets more accustomed and numb to animal cruelty.

I haven’t found any figures for the number of animals that are kept alive in markets. Regarding the sale of live fish, page 48 in FAO’s SOFIA 2018 report claims that:

Live fish is principally appreciated in eastern and southeastern Asia (especially by the Chinese population) and in niche markets in other countries, mainly among immigrant Asian communities. Commercialization of live fish has grown in recent years as a result of technological developments, improved logistics and increased demand.

The report also claims that 45% of fish are utilized as “Live, fresh, or chilled”. Based on this, I suspect that the number of fish suffering in markets could be very significant. From videos I’ve seen, it seems that fish in wet markets are held in very bad conditions. However, I'm unsure if fish in these videos are actually alive, or if their bodies are moving despite their brains being dead.

In addition to wet markets, fish are also sometimes sold in supermarkets where they can also be kept in bad conditions (e.g., see this video). In Poland, Lithuania, and probably some other countries, some animal organizations have addressed this problem.

Animals bred to be hunted

In some countries, animals are bred to stock areas for hunting. This is called game farming. The scale of game farming seems to be significant:

• UK. AnimalAid claims that every year in Britain, around 50M pheasants and partridge are mass-produced in cages, hatcheries, sheds and pens so that they can be shot down by people as a sport. Similarly, according to table 2 in Aebischer (2019), about 39M–57M pheasants and 8.2M–13.4M partridges were released in the UK in 2016. It also mentions that mallards are also released but the number is not reported. Some other sources claim that around 35M birds are released in Britain annually but don’t provide an explanation for their claims.^[25]
• U.S. According to this video, some of the pheasants are released for hunting in the U.S., while others are slaughtered for meat. According to the table 30 of 2017 U.S. Agriculture census, there were 2.5M pheasants farmed in the U.S. at any time. The table also shows that there are 0.8M chukars farmed in the U.S. and they also seem to be farmed to be hunted.
• South Africa. Contrary to Britain and the U.S., South Africa’s game farms seem to mostly raise big mammals. According to Dall (2019), there are around 12,000 game ranches in South Africa. According to this presentation, there were fewer than 400,000 mammals in private game farms in 2015. I’m unsure if this includes all the animals because if both statistics are correct, there would be only 400,000 / 12,000 = 33 animals per farm. van der Merwe (2016) claims that there are an estimated 8,000 lions in South Africa’s game farms.

Animals are also raised in game farms in France, Namibia, Kenya and probably many other countries. In Austria, animal activists have achieved a ban on the hunting of bred animals in enclosures.

Mercy releases (fangsheng)

Mercy release (also known as fangsheng, live release, and prayer animal release) is an old Buddhist tradition of releasing captive animals to demonstrate compassion, create good fortune, and earn merit. Practitioners may think that they are doing animals a favor by releasing them and saving them from slaughter. However, HSI (2009) claims that the vast majority of animals used in mercy release were captured for the sole purpose of being released. It also claims that these animals are often injured during trapping, may starve or suffocate during transport, and when they’re kept in crates for days or weeks. Released animals often fail to survive due to injuries or being released into the wrong habitats. The ones who survive sometimes become invasive species and cause problems for native species (Everard et al. (2019)). Aiying (2018) describes the practice in China and claims that most released animals there are captive-bred and thus can’t survive in the wild. Many are also caught again soon after the release and then resold for another release.

HSI and some other animal charities are (or were) working to educate Buddhist about the harmful effects of mercy releases and lobby government bodies to ban the practice (see HSI (2013), Falconer (2009))

There seem to be no estimates of the number of animals released around the world. However, some estimates suggest that the numbers could be significant:

• Gilbert et al. (2012) estimated that over a 13 months period, 0.7M birds were sold for mercy release in two observed sites in Phnom Penh, Cambodia. The article also claims that Chan (2006) estimated annual sales of 0.7M–1M birds for release in Hong Kong, but I wasn’t able to verify the claim.
• Some animal welfare groups claimed that 200M wild and captive-bred animals are set free in Taiwan every year, ranging from insects to monkeys (Agoramoorthy and Hsu (2005), Falconer (2009)). However, I haven’t found how this was estimated. Hence, I think this estimate should be given little weight.

Note that some individual releases may involve very many animals. For example, a famous vegetarian actress Zhang Jingchu, who is also an animal advocate, released 470,000 fishes (pond loach, whose average weight is 20-30g) in just one go of mercy release.

Zoos

Frynta, Šimková, Lišková, & Landová (2013):

According to the ISIS (International Species Information System) online database, more than 7 million individual animals are kept in 872 zoos and aquariums (as recorded by the date of 12th January 2011).

I wasn’t able to confirm this claim. Furthermore, Mucha (2017) claims that the same database contains information on 3.5M animals. The website of the database claims that they have information about 10M animals, “living and historic”. It could be that Frynta, Šimková, Lišková, & Landová (2013) mistakenly included historic animals in the 7M figure.

There are also some claims about the number of animals in zoos by animal advocacy organizations, but they seem to be unsubstantiated. RSPCA claims that “600,000 birds and mammals are kept in the world’s zoos.” Freedom For Animals claims “at least 7,500 animals – and possibly as many as 200,000 – in European zoos are ‘surplus’ at any one time” and that “animals are regularly ‘culled’ in UK zoos.”

Note that these numbers don’t include animals who are fed to carnivorous zoo animals. According to a private conversation with a former zoo employee, some zoos raise mice and rats to feed their animals. These rodents may be kept in conditions that are similar to conditions of rodents farmed for pet snake food (described in Šimčikas (2019c)).

Circuses

Harris et al. (2006) claims that “there are between 2,400 and 5,900 wild and domestic animals in circuses in Europe.” Savonitto (2017) provides numbers of wild circus animals in some countries: more than 2,000 in Italy, more than 900 in Germany (excluding camelids), 762 in Portugal. It also claims that there are 300 circuses with wild animals in the EU, 205 of which are in Italy, Germany, or Portugal. I haven’t found numbers for animals in circuses in other parts of the world.

Other animals used for entertainment

According to World Animal Protection (2014), there are:

• around 16,000 Asian elephants in captivity worldwide used for tourism rides and performances.
• “1,600 or more” captive bottlenose dolphins used for dolphin entertainment worldwide.
• 3,000 baby macaques taken from the wild annually to be used for performances.

There are many other entertainment-related purposes for which animals are kept in captivity that I haven’t tried to find estimates for. Here are links to Wikipedia articles about some of them:

• Fighting animals
  • Cockfighting
  • Dog fighting
  • Animal-baiting
  • Bull wrestling
  • Camel wrestling
• Racing animals
  • Bull racing
  • Camel racing
  • Goat racing
  • Pigeon racing (see PETA's page about it)
  • Sled dog racing
  • Turtle racing
  • Yak racing
• Rodeo
• Dancing bears
• Hunting dogs

There are also numerous horse-related activities listed here.

Pets

While many people take good care of their pets, technically pets also live in captivity. Hence, I included their numbers in this article as well.

Euromonitor International has statistics on the number of pets in 53 countries^[26], which account for about 70% of the world’s human population. The combined data from all of these countries is summarized in the table below. The dataset excludes most African countries, Pakistan, Bangladesh, Myanmar, and many smaller countries. Statistics in the table below are projections based on a variety of sources: publicly available data, expert interviews, government statistics, etc.

I found several other sources about the number of pets in various regions. I summarized them in the table below:

Sources claim that they conducted the following surveys to arrive at these estimates:

• AVMA (2017) - a survey of 50,000 pet-owning households.
• APPA (2018) - a survey distributed online to a nationally representative sample of 22,202 respondents from a panel. There are some issues with the methodology used in APPA (2018) and AVMA (2017) that are reviewed in Cuddington (2019). It suggests that APPA (2018) may have overestimated pet numbers.
• PFMA (2019) - face-to-face interviews of a representative sample of 8,000 respondents.
• FEDIAF (2018) provides estimates of the number of pets in each European country. The document claims that “the figures are from FEDIAF and its member associations, pet food companies and estimations based thereupon.” Numbers for the UK seem to be based on PFMA (2019). I don’t know what the sources are for the figures for other countries. The 300M figure for pet fish is only mentioned in a footnote, which suggests that this figure is less reliable.
• AMA (2016) - a survey of a representative sample of 2,022 Australians.
• CAHI (2019) - a survey of over 3,026 pet-owning households
• 2019 Chinese Pet Industry White Paper - I couldn’t access the primary source. I took figures from articles citing the white paper ([1], [2]). 2017 Chinese Pet Industry White Paper estimated pet numbers using government data and pet market research.

Most of these numbers are similar to the ones provided by Euromonitor, and it is very likely that these surveys informed Euromonitor projections. However, the estimates of dog and cat in the 2019 Chinese Pet Industry White Paper are much smaller than the estimates by Euromonitor. Both sources agree that the Chinese pet population is growing at a fast pace.

Coren (2012) estimates that “the best guess would be that there are at least 525 million dogs on our planet.” The estimate includes some unowned dogs but claims that it underestimates their numbers. However, the article doesn’t provide sources for its claims. The provided numbers for various regions differ significantly from the Euromonitor data.

De Silva and Turchini (2008) estimate that in 2006 there were 167M domestic cats within the highly industrialized regions (USA, EU, Japan, Canada, and Australasia), 70M domestic cats in the rest of the world (excluding China). Another source with figures for the number of pets in more countries is Batson (2008). However, the estimates in these sources are now more than a decade old.

Note that dogs, cats, and other carnivorous pets eat meat, which increases the number of animals who are farmed for food. Thompson (2008) claims that pet food ingredients include meat and meat byproducts. Note that even when byproducts are used, it still supports the meat industry as it allows them to get extra revenue.

In Šimčikas (2019c), I estimated that there are 4.2M–7.8M pet snakes in the world. Since snakes are reptiles, their numbers are included in the reptile numbers in the table above. Some claim that pet snakes and other pet reptiles face significant welfare issues (see Howell and Bennett (2017), Pasmans et al. (2017), Warwick et al. (2018) and Humane Society factsheet).

One group of pets that is not explicitly mentioned in the table above is exotic animals. Millions of exotic animals are either taken from the wild or captive-bred and then sold as exotic pets. There seems to be substantial suffering involved in the transport of these animals. Furthermore, many of them are unsuitable to be pets. Hence, they lead short and stressful lives in captivity. (Nowak (2016), Actman (2019)).

Ornamental fish (fish in aquariums)

I suspect that there is more uncertainty about the number of pet fish than the number of other pets. According to Euromonitor, there are only 1.15M pet fish in the UK. In contrast, OATA (2019) claims that over 100M fish are kept in aquariums and ponds in the UK. However, the claim by OATA (2019) is unsubstantiated. On the other hand, Euromonitor estimates that there are 198M pet fish in China (172M in 2014), but petfairasia.com claims that it was only 80M in 2014.

Note that in addition to pet fish, there are also other ornamental fish used in public aquariums and elsewhere. However, their numbers seem to be much lower. Raja et al. (2019) claims that 99% of the global ornamental fish market is confined to hobbyists, and less than 1% is used for public aquariums and research. Similarly, Smith et al. (2012) claims that out of 1.1B ornamental fish imported to the U.S. between 2000 and 2006, 99% were intended for commercial sale in the pet industry. Neither of these articles backs up their claims with sources.

The number of ornamental fish bred per year seems to be even higher than the number of pet fish alive in households:

• According to table 5 in the 2013 Census of Aquaculture, more than 232M ornamental fish produced in the U.S. were sold in 2013.
• Satam et al. (2018) claims that more than 2B live ornamental fish are traded, presumably per year (no source is provided).
• Cheong (1996) claims that an estimated 1B ornamental fish are traded annually (no source is provided). It also claims that the bulk of ornamental fish are farm-bred, but some are wild-caught.

Note that the number of fish traded doesn’t include fish that are sold as pets domestically.

Stevens et al. (2017) claims that transportation and handling of ornamental fish imposes a range of stressors that result in mortality at rates that range between 2% and 73%. As I understand it, this is the mortality of fish before they are sold. The article reviews various ornamental fish welfare problems and concludes that it is a major concern.

Closing thoughts

China

There were three large groups of farmed animals I personally didn’t know about before writing this article: quail, frogs, and turtles. All three of these groups of animals seem to be primarily farmed in China. Hence, establishing animal advocacy in China could be even more important than I previously thought. As for the numbers of these animals, it could be that someone who can read Chinese could quickly find more accurate estimates.

Numbers is not all that matters

While in this article I focused on numbers and I think that they are very important, I don’t mean to imply that numbers are all that matters when choosing which group of animals to try to help. For example, if the goal is to reduce suffering, other factors that may matter include:

• Tractability (how difficult it is to make progress on the issue)
• The intensity of suffering of involved animals
• The probability/level of consciousness of involved animals
• The speed of the subjective experience of involved animals (see Tomasik (2016))
• How much does tackling the issue contribute to the moral circle expansion, the growth of the animal advocacy movement, etc.
• The effect that tackling the issue will have on humans and the environment
• Personal/organizational fit of the person or organization that is taking action

For example, the number of fish that are cooked and then eaten while they are still partially alive is probably not very big. However, campaigning against the practice could invoke a public outrage, get more people involved in the animal welfare movement, and be a step towards making compassion for fish more mainstream. It could be a good first issue to tackle in countries that don’t yet have an established animal advocacy movement (e.g., China). The gained momentum could eventually be used to help other groups of animals. Note that I am very uncertain about this particular suggestion, I’m just using it as an example of why we might not always choose to tackle the issues concerning the biggest groups of animals.

This article doesn’t show the full picture

One of the goals of this article was to provide a list of options for what kind of problems animal advocates could tackle. However, the list is incomplete because it doesn’t cover issues related to invertebrate and wild animal welfare. It could be that tackling these issues is even more important than helping vertebrates in captivity.

I probably also missed some other groups of vertebrates kept in captivity. If you know of any such groups of a substantial size, or if you know of better sources about the number of individuals in any of the groups, please leave a comment.

Links to other articles about animal numbers

• Animal Advocacy By Numbers by Faunalytics
• Animal Welfare Issues page at worldanimal.net
• Farm animal statistics - a spreadsheet by the Open Philanthropy Project that estimates how many animals are in each country
• How many neurons are there?
• How Many Wild Animals Are There? By Brian Tomasik
• Our World in Data page about meat production
• The biomass distribution on Earth by Yinon M. Bar-On, Rob Phillips, and Ron Milo
• Trends in meat production by Animal Charity Evaluators

Appendix 1: Comprehending the numbers (seconds of silence)

It can be difficult to comprehend and compare estimates of animals listed in this article because we are not used to thinking about such huge numbers. One way to get a better intuitive understanding of the numbers is to convert them into units of time. This can help because we are more used to thinking about units of time of very different magnitudes (e.g., one second versus one year).

The table below presents the same numbers as the ones in the summary tables at the beginning of the article, except that all numbers are converted into units of time. Instead of showing how many animals humans slaughter, breed, or use per year, the fourth column shows how much time it would take to commemorate every 10,000 animals humans slaughter, breed, or use per year with one second of silence. Instead of the number of animals alive at any time, the second column shows how much time it would take to commemorate every 10,000 animals kept in captivity with one second of silence. The table can also be explored in this spreadsheet.

Appendix 2: Different presentation of the animal numbers

In the table below, I present the same numbers as in the summary tables at the beginning of the article, but not grouped by species category, as this may be easier to navigate for some people. This table can also be explored in this spreadsheet.

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This essay is a project of Rethink Priorities. It was written by Saulius Šimčikas. Thanks to David Moss, Marcus A. Davis, and Kieran Greig for reviewing drafts of this post and making valuable comments. Special thanks to Sabrina Ahmed who contributed to parts of the text.

Notes

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1. Argentina, Australia, Austria, Belgium, Brazil, Bulgaria, Canada, Chile, China, Colombia, Czech Republic, Denmark, Egypt, Finland, France, Germany, Greece, Hong Kong, Hungary, India, Indonesia, Ireland, Israel, Italy, Japan, Malaysia, Mexico, Morocco, Netherlands, New Zealand, Norway, Peru, Philippines, Poland, Portugal, Romania, Russia, Saudi Arabia, Singapore, Slovakia, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Thailand, Turkey, USA, Ukraine, United Arab Emirates, United Kingdom, Vietnam. ↩︎

2. Unfortunately, the statistics don’t specify which species of frogs are primarily farmed in China. Countries for which species is specified seem to mostly farm American bullfrogs, except Thailand, which grows east Asian bullfrogs. Gratwicke et al. (2010), Moreira, Henriques, and Ferreira (2013) and Warfield (2018) claims that frog farms mainly focus on American bullfrogs, but I’m unsure what this claim is based on. FAO claims that frog aquaculture production that is not identified by species undoubtedly contains the production of American bullfrogs, but the proportion is unknown. Martinsen (2010) indicates that there is some pig frog farming in China. According to Altherr, Goyenechea, and Schubert (2011), “approximately a dozen frog farms are producing American bullfrogs and other frog species.” ↩︎

3. This is based on the following claims:

   • FAO page on American bullfrog farming claims that fitter individuals can reach market size (>180 g), in 3 months after metamorphosis.
   • Ayres et al. (2015) considers American bullfrog slaughter weights between <100g and >251g and recommends slaughtering at the weight of 201g.
   • Lutz and Avery (1999): “If the primary market product will be frog legs, harvest can begin when individual frogs reach approximately 175 grams (6 ounces), which should be in about 6 months. If skins are also to be used for leather, frogs can be grown to 250 grams (9 ounces) or even larger.”
   • Table 1 in Moreira, Henriques, and Ferreira (2013) claims that slaughter weight per frog in an observed pond was 300g.
   ↩︎

4. Lower bound: 100,379 tonnes / 350 g = 287M. Upper bound: 100,379 tonnes / 100 g = 1B ↩︎

5. It seems that the Gratwicke et al. (2010) estimate is based on the fact that “a kilogram of export-quality frog legs requires 10 to 40 individual animals” and that according to FAO fisheries data, in 2006 world produced 75,000 tons of farmed frogs and 8,000 tons of wild-caught frogs (about 80M kg in total). Based on this, it seems that the paper estimates that 0.8B (80M ✕ 10) to 3.2B (80M ✕ 40) frogs are consumed each year. However, in FAO’s FishStatJ, I see that 75,000 and 8,000 figures are for live weight in tonnes, not frog-leg weight. It also seems that the paper confuses tonnes with tons but that only has a slight impact on the estimate. ↩︎

6. According to FAO, “precocious tadpoles become froglets in 45 days, while most of the population achieves this in 90-120 days, and a small portion of the cohort (7-12 percent) will metamorphose after one year or more, even in tropical conditions.” For the purpose of the estimation, I’ll assume that the average is in the range of 60-150 days (or 2 to 5 months). FAO also claims that “under tropical conditions, in 3 months after metamorphosis, and sexual maturity in as early as 7 months after hatching, while weakest may take over one year.” According to table 1 in Lutz and Avery (1999), bullfrogs typically reach the weight of 175g in 8 months after metamorphosis. Later, the article seemingly contradicts itself by claiming that they reach the weight of 175g in about 6 months. Based on this, it seems that American bullfrogs are slaughtered 4 months to 8 months after metamorphosis on average. Hence, the slaughter age of American bullfrogs from hatching to slaughter seems to be between 6 months (2+4) and 13 months (5+8). Moreira, Henriques, and Ferreira (2013) claims that the production has 1.5 cycles per year (egg phase up to slaughter weight). If I understand it correctly, that means that frogs live up to 12 / 1.5 = 8 months, which is within my estimated range. This video about “asian” frogs claims that “[i]t may take a year, or longer, for tadpoles to transform into young frogs. Growing a frog to a marketable size frequently takes another two years, or three years total from eggs to harvest.” Martinsen (2010) claim that farmed pig frogs reach maturity in just three months. This suggests that other farmed frog species may have significantly different lifespans. Due to this, I subjectively change the range from 6-13 months to 4-20 months. ↩︎

7. Lower bound: 290M ✕ 4 months / 12 months = 96.7M. Upper bound: 1B ✕ 20 months / 12 months = 1.67B ↩︎

8. Note that FAO may not be reporting numbers for all countries. For example, according to table 8 in the 2013 U.S. aquaculture census, 3.6M farmed turtles were sold “whole” in the U.S. in 2013, but they are not included in FishStatJ. I’m also unsure why the table 7 in FAO’s The State of World Fisheries and Aquaculture 2018 report has slightly higher numbers of Chinese softshell turtle production than FAO’s FishStatj. The difference for 2016 is 4%. ↩︎

9. According to a Fishcount estimate, China produced 22B-68B fish in 2010. China’s aquaculture production in weight increased substantially between the early 2000s and 2010, so the number of fish produced in the early 2000s was probably lower. Hence, 600B-700B fry produced by China in the early 2000s would imply more than a 90% mortality rate, which I’d find surprising. However, it could be that some of the fry were used for fish stocking or some other purposes. Finally, it’s possible that these numbers refer to the number of fish eggs produced and that many of these eggs don’t hatch or that many fish die in hatcheries soon after hatching. ↩︎

10. This is estimated as follows. Lower bound: 35B ✕ 8 days / 365.25 days = 0.8B. Upper bound: 150B ✕ 3 months / 12 months = 50B ↩︎

11. See “Species for asphyxiation estimate” tab in this spreadsheet. Note that I summed up various species of herring, cod, whiting, sole, dab, and plaice, even though the time it takes for these species to suffocate is probably different. ↩︎

12. Lower bound estimation: 30B ✕ 25 minutes ✕ 50% / 525600 minutes = 0.71M. Upper bound estimation: 102B ✕ 250 minutes ✕ 100% / 525600 minutes = 48.5M. 525600 minutes is the number of minutes there are in a year. ↩︎

13. Romeo (2019) claims that Ars Italica’s farm houses 300,000 sturgeons and that Ars Italica and Calvisius Caviar together stretch over 250 acres and produce 28 tons (which is 25.4 tonnes) of caviar per year. According to a video from Calvisius Caviar website, their farm stretches 150 acres. If we assume that the farm area is roughly proportional to the number of fish in the farm, we get that Ars Italica produces around 25.4 ✕ (250 - 150) / 250 = 10.16 tonnes of caviar. Bronzi et al. (2019) claims that the world’s caviar production is 364 tonnes. Using this information, we can extrapolate that there are 300,000 ✕ 364 / 10.16 = 10.75M sturgeons in caviar farms in the world. This extrapolation is very uncertain for multiple reasons. The biggest one is that there are many different sturgeon species being farmed.

    Note that Romeo (2019) claims that 25 tonnes of caviar produced by the two farms in Italy amounts to 15% of the world’s caviar. However, Bronzi et al. (2019) claims that the world’s caviar production is 364 tonnes, which suggests that the two farms produce 25 tonnes / 364 tonnes = 7% of the world’s caviar. I’m unsure why there is this inconsistency, but for this estimation, I used the Bronzi et al. (2019) figure because it provided much more detail about the figure. ↩︎

14. According to the table 30 in the Census of Agriculture, in 2017 in the U.S., there were 368.2M layers, 130.5M pullets, and 7M roosters. So the total number of chickens involved in egg production in the U.S. is about 368.2M+130.5M+7M=505.7M, which is 37% higher than the number of hens. If we increase the 7.5B figure for the number of hens in the world by 37%, we get 10.3B. 10.3B is likely an overestimate of the number of chickens involved in egg production because we already know that the UK included roosters and pullets in the hen numbers. Similarly, the 7.8B is likely an underestimate because the U.S. did not. ↩︎

15. Extrapolations assumed that the ratio between chicken slaughters and broiler breeders alive at any time is similar in different countries and years. If broiler mothers in different countries lay a similar number of eggs per month, these estimations should be roughly correct. They might still be a bit inaccurate because:

    • I don’t take broiler mortality rates into account
    • As explained in the appendix of Šimčikas (2019a), not all chicken slaughters that are included in the statistics are broilers. E.g., U.S. statistics include “spent” hens who are slaughtered when their egg production slows down. For some countries, chicken slaughter totals also include other slaughters of other species of birds.
    ↩︎

16. According to USDA’s Chickens and Eggs 2017 Summary, there were about 56.5M broiler mothers and 3.3M egg-laying hen mothers in the U.S. in 2017. That means that meat chicken mothers make up around 94.5% of all chicken mothers in the U.S. According to Table 30 in the 2018 Census of Agriculture, in 2017, there were 7M roosters in the U.S. My guess is that about 7M ✕ 94.5% = 6.6M of them are used for meat chicken production. It follows that in the U.S., for every meat chicken father, there are 56.5M/6.6M = 8.56 mothers. If we assume that this ratio holds in other countries, we can then estimate that there are between 40M (350M / 8.56) and 70M (600M / 8.56) meat chicken fathers in the world. ↩︎

17. E.g., Minvielle (2004) numbers for China seem to be based on a source that is from 1991. Many other numbers are taken from Minvielle (1998) which cites other sources that were published between 1991 and 1997. Minvielle (2004) also seems to be the ultimate source for Lukanov (2019) claim that “over nine billion quail are produced each year in East Asia”, which means that the claim is also outdated. Furthermore, Minvielle claims that there are over nine billion quail eggs produced, not nine billion quail, as Lukanov (2019) claims. ↩︎

18. Estimate of the number of quail alive at any time in countries other than China: 36M (Brazil) + 7.4M (U.S.) + 6M (Spain) + 3.6M (France) + 2.3M (Italy) = 55.3M. Estimate of the number of quail slaughtered in these countries: 43M (Brazil) + 23M (U.S.) + 66M (Spain) + 38M (France) + 24M (Italy) = 194M. The 43M figure for Brazil is an educated guess. It seems that most quail in the country are raised for eggs. da Cunha (2009) claims that in China, quail have a 10-month productive period. 36M × 12 months / 10 months = 43M. ↩︎

19. I found the following sources that could be useful if someone wanted to try to estimate the number of birds involved in down and feather production:

    • Schmitz (2016) claims that about 186M kg of down and feathers are traded annually
    • Buckland and Guy (2002) claims that 80g-120g of down and feathers are obtained per geese plucking
    • Kozák (2011) goes into more detail about how much down and feathers can be obtained from geese and other birds

    However, I don’t know. the following:

    • How much down and feathers are consumed domestically (and hence not traded)
    • What proportion of down comes from geese and what from ducks or other birds,
    • How prevalent is live-plucking, and how many times are birds live-plucked before slaughter on average.

    Also, I don’t feel like I have a good enough understanding of the down and feather production to produce an estimate. ↩︎

20. Swiftlet farming is conducted in man-made buildings that imitate cave-like environments in order to provide alternative nesting sites and attract swiftlets. The farmers do not control the birds’ movement, breeding or their diets. The swiftlets tend to live without interference and appear to recover well once their nests are removed, as long as this does not occur before their young reach a certain age. ↩︎

21. I think that FAO statistics include at least some working animals because there are countries like Afghanistan, Chad, and Ethiopia that have millions of asses alive, but no asses slaughtered for meat. When googling, I see evidence that articles like this and this about asses being used as work animals in these countries. Finally, articles like Church (2014) and Brooke (2015) that cite FAO statistics and claim that nearly all horses, mules and asses included in FAO statistics are work animals. ↩︎

22. Here are some of the estimates of the number of working animals in the world:

    • Chirgwin (1996): “Considering all the different types of farm animals, the number used worldwide as work animals is estimated at no less than 250 million and may well be over 300 million.”
    • Wilson (2003): “Information on draught animal numbers is scarce although estimates of 300 million animals are sometimes used”
    • According to Wilson (2003), Pearson (1999) claims that “51% of the 921 million cattle in the developing world in 1994 were used for work as were 35% of 135 million buffalo, 65% of 43 million horses, 87% of 43 million donkeys, 70% of 14 million mules and 15% of 19 million camels “. In total, that would be nearly 600 million mammals.
    • Worldanimal.net claims that “the animal work force is estimated at about 300 million animals and the numbers are rising.” It seems that this article uses a broader definition of working animals,to include the ones used in therapy, herding, hunting, etc. However, this may have a limited impact on the estimate because it claims that “the majority of working animals are involved in transport and agriculture.”
    • The International Coalition for Working Equids claims that “an estimated 200 million working animals are essential to the livelihoods of some of the poorest communities worldwide.”

    Note that none of the sources I’ve seen explained how they arrived at the cited estimates. ↩︎

23. The name of the item is “Rodents, other”. I’m unsure why there is “other” in the description since there are no other rodents on the list. Perhaps it’s because rabbits and hares are sometimes mistakenly classified as rodents. ↩︎

24. USDA (2000) also contains the following sentences: “One commercial breeder claims that five percent of the total number of rats and mice bred in the United States-some 200-400 million in all--are bred for research. Researchers are reasonably certain that they have identified those producers. However, the individuals and/or small companies that produce rats and mice for other purposes-- an estimated 190 to 380 million animals--have not been clearly identified through the research.” I’m unsure what are those other purposes. One of them is almost certainly feeding pet snakes and other carnivorous animals kept in captivity. ↩︎

25. • The League Against Cruel Sports claims that around 35M pheasants and partridge are released on the UK shooting estates each year
    • Humphries (2019) claims that there are 30M pheasants and 6M partridge reared on British game farms.
    • Game and Wildlife conservation trust claims that an estimated 35M pheasants are released each year.
    ↩︎

26. Argentina, Australia, Austria, Belgium, Brazil, Bulgaria, Canada, Chile, China, Colombia, Czech Republic, Denmark, Egypt, Finland, France, Germany, Greece, Hong Kong, Hungary, India, Indonesia, Ireland, Israel, Italy, Japan, Malaysia, Mexico, Morocco, Netherlands, New Zealand, Norway, Peru, Philippines, Poland, Portugal, Romania, Russia, Saudi Arabia, Singapore, Slovakia, South Africa, South Korea, Spain, Sweden, Switzerland, Taiwan, Thailand, Turkey, USA, Ukraine, United Arab Emirates, United Kingdom, Vietnam. ↩︎