By Julia Galef
If you're bothered by the idea of killing animals for food, then going vegetarian might seem like an obvious response. But if you want your diet to kill as few animals as possible, then eschewing meat is actually quite an indirect, and sometimes even counterproductive, strategy. The question you should be asking yourself about any given food is not, "Is this food animal flesh?" The question you should be asking yourself is, "How many animal lives did this food cost?"
That might seem like an odd question for a vegetarian to have to concern himself with, but producing foods like eggs, milk and cheese - all of which are permitted on a typical vegetarian diet - does kill animals. Harvesting eggs and dairy doesn't, in theory, require us to kill the laying hens or dairy cows, but in practice, modern factory farms do kill their hens and cows, at whatever point in the animals' life cycles the farm considers to be the most profit-maximizing. For dairy cows, that's usually at age 3-5, out of a natural 20-25 year lifespan. For egg-laying hens, it's usually after one or two laying cycles. And since the male chicks of the laying species are useless to the egg farmer, they're killed right after they hatch.
In order to estimate roughly how many animals die to produce each kind of food, I scrounged up some data on the typical amount of meat, eggs, and dairy that we get out of a modern farm animal, and combined it with data on the calorie counts of those foods. That allowed me to calculate the number of calories of food that we get out of each type of animal, or more to the point, the "lives-per-calorie" statistic for each food. The results are below, with the foods ordered from "kills the fewest animals per calorie" to "kills the most animals per calorie." (All numbers are approximate, of course, but they're from as recent and reliable sources as I could find. Detailed citations are at the end of this post.)
http://blogs.scientificamerican.com/guest-blog/files/2011/08/Chart.jpg *The yield for a laying hen over its lifetime is actually about 550 eggs, but I've divided it by two to account for the fact that approximately one male chick is killed for every laying hen.
The most striking result that falls out of this calculation is that eating eggs, as many vegetarians do, kills more animals than eating red meat. That's primarily due to the vast size difference between chickens and cows or pigs. While you only need to kill one single steer to get about 450 pounds (405,000 calories) worth of meat, you'd need to kill about 20 chickens to get enough eggs to match that number of calories.
In fact, the lives-per-calories cost of eggs is so many times higher than that of beef that even a small amount of eggs outweighs the life cost of a larger amount of beef. So, for example, let's say you're a vegetarian and you go out to lunch with your omnivorous friend, where he orders a burger and you order an egg-salad sandwich. The two eggs in your sandwich are only 150 calories, compared to the 300 calories in his beef patty, but the eggs cost almost 9 times as much life as the beef.
This isn't to say that vegetarianism is pointless. The typical vegetarian almost certainly causes fewer animal deaths than the typical omnivore. And unless you're replacing all of your meat calories with egg-calories, going vegetarian will significantly reduce the number of deaths your diet is causing. The important takeaway from these calculations, rather, is that evaluating food in terms of "flesh" versus "not-flesh" doesn't tell you that much about how many animals died to produce it.
Of course, the number of animal deaths isn't the only thing you might care about if you're concerned about animal welfare - there's also the very important question of how much suffering the animals experience. Looking at suffering instead of number of deaths would change the calculations somewhat, but I suspect the overall verdict would remain similar if you were looking at suffering-per-calorie - or, if anything, things would look even grimmer for egg-lovers. Laying hens arguably lead some of the most miserable lives out of all livestock, spending all their time crammed into cages with less space than half a piece of paper, having their beaks cut off, and being starved to induce molting. (The male chicks would count less if you're looking at suffering-per-calorie, however, since their lives are so short.) It's also worth noting that lives-per-calorie calculations also don't take into account impact on the environment. Raising beef is arguably the worst industry in terms of things like producing greenhouse gases, breeding antibiotic-resistant bacteria, and requiring huge amounts of farmland just to feed the cattle. So there's still a good case for choosing eggs over beef in the sense of minimizing your environmental impact, but that doesn't change the fact that you'd be making a tradeoff: killing more animals to hurt the environment less.
Citations: According to the USDA http://www.nass.usda.gov/Charts_and_Maps/ Milk_Production_and_Milk_Cows/cowrates.asp , the average dairy cow produced 21,000 lbs of milk last year, and according to several sources, the average dairy cow is culled from the herd after about 3 years, so I multiplied 21,000*3 to get the average amount of milk produced over the lifetime of a dairy cow. It takes about 1 gallon of milk to produce 1 lb of cheese, and there are about 8.5 lbs of milk per gallon, so I divided 63,000 lbs by 8.5 to get the 7,400 lbs of cheese figure.
The figures on beef http://measureofdoubt.com/2011/06/22/why-a-vegetarian-might-kill-more-animals-than-an-omnivore/www.ok.gov/~okag/food/fs-cowweight.pdf and pork http://measureofdoubt.com/2011/06/22/why-a-vegetarian-might-kill-more-animals-than-an-omnivore/www.ok.gov/~okag/food/fs-hogweight.pdf come from the Oklahoma Department of Agriculture.
The average number of eggs http://usda.mannlib.cornell.edu/usda/current/ChickEgg/ChickEgg-02-25-2011.pdf per laying hen per year comes from the USDA, and I multiplied by two because that's the most common figure I found for the number of laying cycles. The average weight of a broiler chicken I got from the USDA's annual Poultry Slaughter publication http://usda.mannlib.cornell.edu/usda/current/PoulSlauSu/PoulSlauSu-02-25-2011_errata.pdf