by Brian Tomasik
First written: 2008; last edited: 7 Sep. 2016


The sign of vegetarianism for wild-animal suffering is unclear, both in terms of short-run effects on wild animals on Earth and in terms of long-run effects on society's values. Compared with veg outreach, other approaches to reducing animal suffering on factory farms, such as humane slaughter, are more clearly positive.

Especially for smaller animals like chickens, it's possible that the direct suffering caused to the farmed animals themselves is of a comparable order of magnitude as the size of the "error bars" of uncertainty I have about how farmed chickens affect insect suffering, which tentatively suggests continuing to oppose chicken consumption, pending further research.

If someone insists on eating meat, I would recommend eating rainforest-raised or grass-fed beef. Rainforest-grown beef very likely reduces net animal populations because rainforests have such high productivity. Grass-fed beef probably also reduces net animal populations, because cows can eat lots of grass that would otherwise feed smaller animals, and given that less of the feed for these cows is farmed grain, the uncertain net impacts of crop cultivation loom relatively less large over the calculation.


Utilitarian vegetarians avoid meat because they realize that animals on factory farms endure more suffering than happiness. They want to reduce the number of animals who have to endure horrific experiences living in cramped conditions and being slaughtered at a young age.

Many vegetarians also assume that their diet choices benefit wild animals.

Some believe wild animals have net positive lives, but this ignores the fact that r-selective reproduction dominates in most species. Insects may live only days or weeks on average before dying in potentially painful ways. It seems very likely that wild animals have net negative lives in aggregate, in which case we would hope to prevent their births, just like vegetarians want to prevent the births of factory-farmed animals.

So what is the net impact of vegetarianism on wild animals? This is a very complicated question, but two big components of the analysis come from crop cultivation and climate change.

Crop cultivation

Eating meat requires moving plant food energy up an extra trophic level in which lots of energy is lost. For this reason, vegetable protein generally requires many times less cultivated grain per gram than does animal protein. Even cows that are grass-fed require lots of grazing, which has some similar effects on wild animals as crop cultivation. Actually, grazing by cows is more clearly positive than is crop cultivation, whose sign I'm still rather uncertain about.

In "Crop Cultivation and Wild Animals," I survey the pros and cons of crop cultivation for wild-animal suffering. I find it somewhat likely that growing crops like legumes/nuts, and maybe vegetables/fruits, is net beneficial to wild animals in the short run. However, growing grains/cereals might actually increase insect suffering because these crops are very productive per hectare. Farm animals are mostly fed grains/cereals (and 91.8% of grain fed to US farm animals is corn), so even though it seems that some crop cultivation helps wild animals in the short run on balance, this is less clear for the crops that farm animals eat.

Climate change

Animal farming is one of the world's biggest contributors to climate change -- both because it requires more energy than equivalent plant farming and because livestock emit greenhouse gases as part of their metabolism. Eating a vegan diet instead of a conventional omnivorous American diet results in 1.485 fewer metric tons of CO2-equivalent gases per year, bigger CO2 savings than from switching to a green car. However, note that the lifetime of methane is only 12 years compared with 30-95 for CO2.

Once again, the question of how climate change affects wild animals on balance is sufficiently complicated that I have a separate essay for the topic: "Climate Change and Wild Animals." The conclusion is that I'm extremely uncertain of the net sign of climate change for wild-animal suffering. That said, once again, reducing climate change is important for global stability and so may be valuable for prospects of compromise to reduce suffering in the future. On balance, we should plausibly be glad about vegetarianism's effect of attenuating contributions to climate change.

Cattle grazing

When cattle eat vegetation on pasture fields, they presumably leave less vegetation left over to be eaten by bugs (and other organisms). Hence, I think it's at least, say, ~60% likely that cattle grazing on the whole reduces bug populations (and hence, bug suffering) on pasture fields. These articles explore this topic further.

Rainforest loss

One article claims that "80% of Amazon Deforestation Stems from Cattle Ranching". Another piece puts the figure at 70%. Given that rainforests are home to some of the highest densities of wild-animal populations (and hence wild-animal suffering) on Earth, this appears to be a consideration in favor of beef consumption.


Manure from factory farms can leach into rivers and contribute to eutrophication in water bodies. The sign of eutrophication on wild-animal suffering is unclear.

Wild-caught fish

Promoting vegetarianism typically involves promoting avoidance of seafood (although in some cases, people move toward eating fish upon learning about factory farming of land animals). The impacts of wild-caught fishing on wild-animal suffering are complex, and I don't have a strong opinion on whether they're good or bad on balance.


Poultry and pigs are sometimes fed wild-caught forage fish. In 2002, 22% of fishmeal and fish oil were fed to poultry, 24% to pigs, and 46% to aquaculture. That leaves only 8% for other uses (some of which include pet food), which suggests that beef is probably not a major consumer of fishmeal? How we evaluate fishmeal depends on the net impact of capturing small wild-caught fish in general.

Despite the above figures, humans still eat most fish of the fish harvest: "Humans ate 130.8 million tons of fish in 2011. The remaining 23.2 million tons of fish went to non-food uses such as fishmeal, fish oil, culture, bait, and pharmaceuticals." Another source claims a slightly higher figure: that 36% of wild-caught fish become fishmeal. The worldwide amount of forage fish fed to pigs and chickens is 6 times the amount of fish eaten by Americans.

How much fish is fed to a single chicken? I assume feeding fishmeal to chickens is mainly something that happens in developing nations. About 10 billion chickens are killed in the US per year. Suppose the total number of chickens fed fishmeal is in the same ballpark: ~1010. The amount of fishmeal fed to chickens is, by the above numbers, roughly: (23.2 million tons) * 0.22 = 5 million tons = 1010 pounds. So it looks like a single chicken is fed on the order of ~1 pound of fish.

There's also a risk that in the future, an increasing number of farms will begin using ground-up insects as feed. Farming those insects would significantly increase total suffering.

Insects as feed

Insect farming has been proposed not just to feed fish but also to feed land farm animals. This article says "If we want to continue our customs of farming and eating animal products on our limited resources, we may have to look to novel alternatives like black soldier fly farming."

Human lifespans

Veg*ans often claim that a veg*an diet will extend your lifespan. I'm skeptical of nutrition studies in general, so I don't know if this is true, but if veg*ism does add, say, 1-2 years to a person's life, that slightly increases that person's environmental impact, which probably reduces wild-animal suffering on balance. I would guess the effect is pretty small, though. For example, say lifelong veg*ism adds 1 year to a lifespan of 75 years. Then it increases a person's environmental impact by ~1/75 = 1.3%. In contrast, choosing veg*an food probably changes a person's total environmental impact by at least like 10-30% or something (I'm just making those numbers up).

Displacing other foods

When people eat more meat, they generally eat less of certain other foods (e.g., tofu, soy milk, beans). So one more effect of meat consumption is reduced consumption of certain other plant foods. (Thanks to Vidur Kapur for this point.) The impact of this on wild-animal suffering is unclear.

Promoting general concern for animals

I don't know the net directional impact of vegetarianism on suffering in the wild. Even if vegetarian diets do increase animal suffering by creating more wild animals, it's plausible that organizations promoting vegetarianism do more good than harm. Exposure to the cruelties of factory farming is one way in which many people are first introduced to the topic of animal suffering in general, and such concern can spill over into other domains, perhaps including suffering in nature. After all, if animals on factory farms would be better off not existing, then if conditions in the wild are for some animals just as miserable, then those animals would be better off not existing as well. And even if wild-animal lives were not on the whole negative, it might still be possible -- perhaps much farther off in the future -- to improve their welfare as is done for farm animals, such as by shifting from ecosystems filled with small, short-lived creatures that die young to ecosystems with larger, longer-lived animals.

General concern for animal suffering is crucial if humans are to make wise choices with respect to wild animals once more advanced technologies arrive, and promoting vegetarianism based on reducing suffering seems generally likely to cultivate such sympathies.

However, advancing vegetarianism from, say, the perspective that humans have no right to interfere with animals or that meat causes destruction of intrinsically valuable nature could be counterproductive. Indeed, I find it likely that vegetarianism increases support for wilderness conservation on balance, and the negative impacts of wilderness preservation on wild-animal suffering could be substantial. This concern suggests that the indirect, memetic effects of vegetarianism could very well be net harmful.

Do wild-animal considerations dominate farm-animal suffering?

Clearly large numbers of wild animals, especially insects, are affected by animal farming. But how does the impact on wild-animal suffering that meat production entails (whether positive or negative) compare with the suffering of the farmed animals themselves?

Gaverick Matheny and Kai M. A. Chan took a stab at this question in reverse in "Human Diets and Animal Welfare: the Illogic of the Larder", where they assumed for the sake of argument that both factory-farmed and wild-animal lives were positive. Ignoring distinctions among animals regarding brain complexity, they found (Table 2, p. 586) that -- when just considering wild mammals and birds -- cows and pigs reduced wild-animal life-years more than the number of life-years added by farming, but for chickens, on-farm life-years dominated wild-animal ones. So if we assume that both farm animals and wild animals have net negative lives, then this calculation suggests that farming of at least broiler chickens (and egg-laying hens) increases total suffering even after the wild-animal impacts of crop cultivation are considered. That said, this calculation ignored cold-blooded vertebrates, as well as invertebrates.

How does the calculation look if we include insects in the calculation? I'll try two different estimates:

Bottom-up estimate

The National Chicken Council estimates that a single chicken, with a typical slaughter age of 48 days, weighs about 6.2 pounds while alive and is produced with a feed-to-meat weight ratio of 1.91. That implies about 12 pounds of feed. In the US, most of that feed is corn, plus some soybeans and other things, but I'll focus on corn, and other crops should be have similar numbers within at most an order of magnitude.

Corn yields 171 bushels per acre-year times 56 pounds per bushel = 9600 pounds per acre-year = 24,000 pounds per hectare-year. So feeding a single chicken over its life requires on the order of 12/24,000 = 0.051% of a hectare-year. However, I'm worried this number is too low, since a good portion of the weight of corn is from corn cobs, which I assume aren't used as part of chicken feed? So let's try an alternate estimate based on calories.

This article reports 1070 calories in a half chicken, which is 2140 in a whole one. Another page estimates 1490 calories in a whole chicken. These numbers don't include eviscerated organs, the head, feathers, etc., so the calories in a live chicken are presumably a bit bigger -- maybe something like ~2500-3000? I'll assume 3000, and I'll approximate the calories-in-to-calories-out ratio for chickens as 2:1, giving 6000 calories of corn needed. Corn yields "roughly 15 million calories per acre" per year, which is 37 million calories per hectare-year. So one chicken requires something like 6000/(37 million) = 0.016% of a hectare-year. This is actually lower than my previous 0.051% estimate. Let's split the difference and call it 0.03% of a hectare-year.

In this discussion, I estimated there might be ~107 insects per hectare on potential crop land. So on the portion of land that's used to feed a chicken, there might be (~107 insects/hectare)*(0.03% hectare-years/chicken) = ~3000 insect-years/chicken. Suppose that in expectation, farming crop land either increases or decreases insect populations by 5%. (The actual difference is probably greater than this, but given uncertainty about even the sign of crop cultivation's impact on insect welfare, the expected impact after a reasonable examination will be closer to 0%.) Then crop cultivation can be expected to create or prevent something like (5%) * (3000 insect-years/chicken) = ~150 insect-years/chicken. Since there may be several insect life cycles per year depending on the species, this might be something like, say, ~300 insects (either created or prevented) per chicken.

Top-down estimate

This estimate is far more hand-wavy, but it's nice to have a second look at the numbers, since many of the figures used above could be off by a few orders of magnitude. One study reported that invertebrate populations declined on average by 45% in recent decades. That number could be too high given that more extreme estimates are more likely to get news coverage. On the other hand, humans have been around for more than a few decades, so maybe the total impact of human activity on invertebrate populations is something like a 45% drop. Given that crop cultivation occupies 11% of Earth's land area, growing crops might contribute a nontrivial portion to the drop (or might increase net insect populations -- it's unclear). Let's say the "error bars" on crop cultivation's impact are 1% of the world's total insect population, i.e., 1% * 1018 = 1016 insect-years per year. Suppose chicken farming accounts for (just making up a number), 1% of that amount, giving error bars for chicken farming of ~1014 insects impacted. Worldwide, there are ~18 billion chickens at any given time. So the insect error bars per chicken-year would be something like (~1014 insect-years)/(~2 * 1010 chicken-years) = ~104 insect-years (either created or prevented) per chicken-year. If the typical insect lives about as long as the typical farmed chicken, this would also be ~104 insect lives created or prevented per chicken. This is about an order of magnitude higher than the bottom-up estimate, but the input parameters are just guesses, so I'm actually surprised it's so close to the bottom-up estimate.

Weighing insects vs. chickens

My intuitive feeling is that 102 to 103 insects' worth of suffering matters about equally as the suffering of a broiler chicken over 48 days of life and a potentially agonizing slaughter. So chicken suffering and the error bars on insect suffering from crop cultivation seem to be pretty close and are probably within a few orders of magnitude.

How about comparing on a per-neuron basis? Carl Shulman estimates that chickens have about 4/1,350 times the brain weight of humans, and since "In terms of neurons per gram of brain mass chickens are very close to humans", this implies about the same fraction of neurons. Humans have 86 billion neurons, so chickens probably have about (86 billion)(4/1,350) = 250 million neurons. Fruit flies have on the order of 100,000 neurons. So the ratio of chicken to insect neurons is on the order of 103 -- about the same as the ratio of (error bars on insects affected)/chicken.

If we weight sentience in proportion to sqrt(# of neurons), the comparison becomes sqrt(250 million) = 16,000 for chickens vs. sqrt(100,000) = 320 for insects, or a ratio of 50:1. In this case, we might think effects on insects are more important than those on chickens.

Given that the sign of crop cultivation for insects isn't even clearly positive or negative, if the variance in the insect effects of chicken farming are only of a comparable magnitude with direct chicken suffering, then we might incline toward opposing chicken farming to be on the safe side, pending more thorough investigation. That said, I haven't considered other effects of chicken farming, including energy use. And if any of the soy fed to chickens is rainforest-grown, this might be significant as well. So the uncertainty remains large. But at least for now, I'd encourage people to pass on the chicken nuggets.

The following figure illustrates my current state of belief regarding this question. The blue error bars might be smaller than what's shown, but given the error bars on my error bars, I kept them reasonably large.