The small body problem is problematic both in terms of the number of animals farmed, and the means by which they are farmed. As we saw above, about 200 chickens are required to produce the same amount of meat gained from slaughtering one cow.⁵ For aquatic animals and insects, the ratio is even more striking. You need 20,321 shrimp to produce the same amount of meat gained from slaughtering one cow.⁶ For crickets, assuming an average weight of 0.2g and a 100% conversion rate into cricket flour, the 5,000 crickets required to produce 1kg of protein results in a cricket to cow death ratio of 1.6 million to 1.⁷

The number of animal lives lost per ton of product produced varies drastically depending on the species – so much so that it is difficult to graphically convey. Here, a line break in the y-axis is required to convey the difference in animal lives lost when comparing cows or chickens to crickets.

Whilst the sentience of some insect and fish species is somewhat unclear, there is substantial evidence that they can suffer.⁸ Moreover, the sheer number of insects or fish required to provide comparable amounts of human nutrition is a particular call for caution: even a small chance of underestimating their sentience threatens an intolerable and avoidable moral atrocity.⁹ 

We have consistently underestimated the capacity of non-human animals to suffer, with devastating consequences for literally trillions of farmed animals. A lack of certainty regarding the sentience of smaller animal species should caution, not embolden, efforts to intensively farm them. 

The small body problem is further compounded by the fact that smaller animals tend to be farmed in worse conditions than larger animals. Again, the typical example here is the cow and the chicken. Whilst we should not condone the typical farming practices of either species, it is generally accepted that one is preferable over the other. 

Cows are more likely to have access to pasture and, compared to chickens, have more space per animal in intensive systems. Chickens are much less likely to ever see the outdoors, and are confined in much more crowded conditions. They experience short lives in ammonia-filled warehouses, sometimes growing so fast that their bones break under the weight of their own flesh. In the US, 70% of cows are factory farmed, compared to 99.97% of chickens.¹⁰

Farming methods for fish are arguably even more problematic (and more poorly understood). Farmed fish welfare standards are limited and often voluntary: in 2015, only 6% of global aquaculture production was certified by the leading voluntary private standards.¹¹  Farmed fish also experience particularly high pre-slaughter mortality rates – Animal Charity Evaluators estimates the pre-slaughter mortality rates for some of the most commonly farmed fishes to be between 15%–80%.¹² Moreover, and crucially, some farmed fish species are carnivorous, meaning even smaller fish are slaughtered for farmed fish feed. For the farming of these carnivorous species (which include salmon, trout, and sea bass), the small body problem is of potentially exponential concern, being relevant both for the feeding and eventual consumption of the fish.¹³

These two factors form the crux of the small body problem. In order to provide the same amount of animal protein, many more small animals need to be slaughtered compared to larger animals, greatly increasing the number of individual farmed animals experiencing suffering. Moreover, the farming methods for smaller animals are often conducive to higher levels of suffering, further compounding the problem.

There is a variant of this problem that is a cause of particular concern to animal advocates. The small animal replacement problem extends the small body problem by recognising not only that consuming smaller animals increases animal suffering overall, but also that there are multiple pressures pushing people to eat smaller animals. 

Meat-eating environmentalists might recognise the impact of beef production on climate change, and so point to chicken as a less environmentally damaging source of animal protein. (A typical example of this argument is presented by a Smithsonian article headline from 2019: ‘Choose Chicken Over Beef to Dramatically Cut Carbon Footprint, Study Finds’).¹⁴ Health professionals warn against the carcinogenic content of red and processed meat (primarily from cows and pigs), and recommend poultry or fish instead¹⁵. Poultry products are also often much cheaper than beef products. According to the UK’s Office for National Statistics, per kilogram, chicken meat and eggs are both less than half the price of beef mince, and almost 5 times cheaper than beef steak (although these comparisons are somewhat dependent on the type of products being compared).¹⁶ All these pressures can encourage consumers to replace their consumption of larger animals, such as cows and pigs, with smaller animals, notably chicken and fish. 

The small animal replacement problem causes a particular challenge for animal advocates. Advocates who appeal to the (often much more tractable) environmental or health concerns regarding meat consumption risk motivating dietary changes not from animals to plants, but from larger animals to smaller animals. A well intentioned campaign that draws on environmental or health concerns to encourage consumers to eat less meat might be successful in reducing some individuals’ beef consumption. However, for those that are not particularly concerned with animal ethics, the impact of the messaging may simply be a transition from beef to other, smaller animals. In other words, the campaign might inadvertently nudge more consumers towards chicken or fish, thereby increasing overall levels of animal suffering. 

We are already seeing a transition in consumption from larger to smaller animals. In the last few decades, chicken has risen from an occasionally luxury product to the most widely consumed animal protein globally. In 1961, chicken made up 12% of per capita meat consumption – by 2021 it more than tripled to 39%, making it the predominant meat consumed per capita per year globally.¹⁷

Moreover, some research suggests that consumers tend towards replacing meat consumption from large animals with meat from smaller ones. One study of 108 patients in a London hospital found that most patients were supportive of taking beef off the menu, but that 72% intended to eat either chicken or fish in its place.¹⁸ 

Particularly given these trends, animal advocates risk having an undesirable effect on meat consumption: a decrease in meat consumption from larger animals, but a resultant increase in meat consumption from smaller animals. This would result in an increase in animal suffering by some orders of magnitude, an effect completely contrary to animal advocates’ primary goal.

At the heart of this problem is a straightforward issue of scale: to gain equal amounts of meat, more small animals than large animals must experience suffering and slaughter. The implications of this problem are significant and multiple.

1. To gain the same amount of meat from one slaughtered cow, roughly 200 chickens must be slaughtered. For small fish and crustaceans, the number can be in the thousands. For insects, millions. Choosing to replace animal meat from larger animals with smaller animals can increase the number of animals being farmed by several orders of magnitude. 
2. Concurrently, there is a tendency for smaller animals to be farmed in more intensive conditions, or to be fed other animals in their feed. This further compounds the small body problem. 
3. Trends already show that the proportion of per capita meat consumption coming from smaller animals is increasing. Moreover, multiple pressures (notably health, environmental, and to an extent economic) are pushing people in the direction of replacing their consumption of larger animals with smaller animals. 

It is worth noting one particular implication of the small body problem: declining meat consumption does not necessarily correlate with reduced animal suffering. If global meat consumption starts declining, even a modest substitution of meat from larger animals with smaller animals could result in far more individual animals experiencing suffering as a result, even as total meat consumption falls.