This essay argues that getting domesticated dogs to eat vegan or ostrovegan diets is a neglected, tractable, and important way to advance justice for animals. First, I estimate that dog diets contribute to the slaughter of 2.89 billion animals on factory farms annually, the vast majority of which are chickens, and create about as much greenhouse gas emissions as Australia. Second, I argue that an (ostro)vegan diet is, as far as we know, healthy for dogs. Third, I suggest some ways we can advance the cause. 

How many animals are slaughtered on factory farms to feed domestic dogs?

Overall, I estimate that dog diets result in the slaughter of 2.824 billion chickens, 56.79 million pigs, and 9.52 million cows. 

On a per-dog basis, switching to a non-meat diet will save about 20 chickens, 0.41 pigs, and 0.07 cows per year. 

Here’s a Google Sheet of my calculations. The remainder of this section explains how I got there.

How many domesticated dogs are there?

700 million dogs live on Earth, about 471 million of whom are domesticated. 

How many of those dogs mostly eat food from factory farms?

Dogs and dog diets are heterogeneous. A street dog who scavenges or gets fed at a temple might plausibly contribute very little or nothing to factory farming. Likewise, a farm dog who eats table scraps or an apartment dog who eats “human-grade food” is going to have a very different dietary footprint. 

For our purposes, I think we want to know how many dogs eat mass-market food that’s packaged and sold as dog food, which we can assume almost entirely comes from industrial farms. For a ballpark estimate, I tally all domesticated dogs in the United States, Canada, Australia and Europe, and assume that ⅔ of the food they eat is meat that comes from Concentrated Animal Feeding Operations. ( Around 99% of all meat in the US comes from factory farms, but dry food for dogs is typically a mix of grains, vegetables and meat.)

Apparently there are 89.7 million pet dogs in the US, 7.9 million in Canada, 6.4 million in Australia, and 104.3 million in Europe — so I'm estimating about 208 million dogs getting ⅔ of their diets from factory farms.

How much does the average dog eat?

A dog food company recommends that a medium-sized dog eat between 1.75 and 2.33 cups (.875 to 1.165 lbs) of food per day. 

Is the average dog a medium-sized dog? I’m not sure. The most popular breeds in America, aside from the French bulldog, tend to be big. But as far as I can tell, that measures the sale of pure breeds, and apparently just over half of American dog owners have mutts.

Here’s a totally unscientific estimate: let’s say that the average domesticated dog weighs about 35 lbs,^[1] and consumes 1 lb of food, and .67 pounds of meat, per day.

How much meat is that in total?

⅔ of a pound of meat per day is about 244.5 lbs per dog per year, so 208 million dogs eating that much is 50,638,640,000 pounds of meat per year.^[2]

What animals produce these 50.64 billion pounds of meat?

 Dog food is a mess of flesh, byproducts, and parts that otherwise wouldn’t be consumed. But let’s roughly assume that all dog food meat comes from chickens, pigs and cows/buffalo, and that the proportions coming from the three categories are the same as those that go into human food. 

Our World in Data estimates that among those categories, about 41% of every pound of meat comes from chickens, about 36% comes from pigs, and about 23% comes from beef.

That gives us about 20.75 billion pounds of chicken, 18.2 billion pounds of pig meat, and 11.6 billion pounds of beef. 

How many animals are killed to feed domesticated dogs?

OWID estimates that for animals slaughtered in America, the average chicken produces 4.9 lbs of meat; the average pig 214 lbs; and the average cow 815.32 lbs. 

That gives us 4.23 billion chickens slaughtered; 85 million pigs; and 14.18 million cows. 

Here, one might object that many of these animals would have been slaughtered anyway, because dog food is partly comprised of byproducts, offal, and the like. How much of this harm is really caused by dog diets? This is hard to estimate without a structural model. Perhaps some of that food would simply go to waste, but presumably much of it would go towards feeding other farm animals (this regularly happens), which would impact food production elsewhere, etc. 

Let’s generously assume that ⅓ of all factory farm meat consumed by dogs is pure byproduct, i.e. does not drive meat consumption at all.

Our final estimate is that dog diets result in 2.824 billion chickens slaughtered; 56.79 million pigs; and 9.52 million cows. That’s 2.89 billion animals slaughtered on factory farms for dog food each year.

There are many different ways to estimate how bad this is, depending on how you convert an animal’s suffering into human-legible terms. For me, these numbers are self-evidently very bad.

Another way to approach this is to think about environmental harms. OWID estimates that every pound of beef produces about 99.5 pounds of carbon emissions. Switching all dogs to vegan diets would cut GHG emissions by about 386 million tonnes, which is about as much Australia currently produces. Cutting meat in dog diets in half would eliminate approximately the same amount of GHGs as are produced by Venezuela or the Netherlands.

Is it healthy to put a dog on a vegan or ostrovegan diet?

This is my good friend Nico, who, along with his person and myself, follows an ostrovegan diet.

Tab 2 of my accompanying spreadsheet provides an overview of Nico’s diet. Nico weighs about 21 pounds. 

When Nico’s person adopted him, they arranged a consultation with a professor of veterinary science at Cornell to ask if a vegan diet was healthy for dogs. The professor said that it was totally fine, that they should be careful about giving Nico a well-balanced diet. That conversation cost about $100. Two years later, Nico is a healthy, happy pup. 

 This professor is also an animal nutritionist with a PhD in  pharmacology who has a research lab and works with canine athletes. He mentioned that most standard vets receive little if any nutrition education. He said that dogs are extremely flexible creatures with unusually plastic nutritional needs. (This is probably why they live pretty much all over the world.) He claimed that any vet who says they can't thrive without meat doesn't know what they're talking about; vegan dogs on appropriate diets should have no health or longevity issues. He did say all dog guardians should rotate foods to prevent any nutritional deficiencies from developing. He recommends only food that is produced in accordance with AAFCO guidelines. He prefers food with added methionine and taurine, and advised that young and active dogs need food with a higher percentage of protein than older dogs do. He also thinks that commercial dog foods tend to be too low in fat, and suggests adding a bit of oil to the dog's food.

Roberts, Oba, and Swanson (2023) test the effects of "mildly cooked human-grade vegan dog foods" on "blood metabolites and fecal microbiota, characteristics, and metabolites" in 12 adult, female beagles, and found that  "the mildly cooked human-grade vegan dog foods tested in this study performed well, resulting in desirable fecal characteristics, ATTD, and serum chemistries...[and] positive changes to serum lipids and fecal metabolites, and interesting changes to the fecal microbial community." This is obviously not a slam-dunk result -- twelve dogs of just one breed --  but our prior here, I think, should be that vegan diets are safe for dogs, as they are safe for us.

Vegan dog diets are likely to be more expensive than meat-based options, and dogs might be less happy with their food. On the other hand, dogs probably don’t like being neutered, but we generally do it anyway because we think the benefits outweigh the costs (whether this is true or not is a fight for another day). Incorporating the needs of non-pet animals into this calculus seems a manageable leap from there. 

The case for supplementing with with bivalves

Ostroveganism is a vegan diet with some bivalves added in — oysters, mussels, and some clams (the ones that don’t move). These bivalves lack central nervous systems, so they probably don’t suffer in any meaningful sense; farming them is relatively good for the environment; and they help provide some nutrients that are otherwise hard for vegans to get (B12 and iron mainly). Peter Singer follows this diet; see Dialogues on Ethical Vegetarianism, pp. 107-109, for more discussion. 

Nico’s person believes that his dried mussels keep his fur nice and sleek, and he seems to really like them.

I’m convinced. How can I help?

First and most obviously, if you have a dog, switch them over to a vegan diet, or get them most of the way there.^[3] My friend Charles, who is a dog, took well to Wild Earth products. The dogs I walk at a local shelter seem to like ETTA SAYS! Peanut butter treats.

I expect a full conversion to take some trial and error, but I think that most dogs can find a non-meat diet that meets their needs and that they’re happy with.

Second, this seems a neglected FoodTech space.^[4] We have some vegan dog food brands, but the modern fancy alternatives tend to be pretty meat-based. While humans make fine-grained distinctions and object loudly when meals don’t meet their cultural expectations, dogs are generally happy to eat, period. I think there’s room here for more entrepreneurship, in particular with cultured meat and fake meat. Ditto for cats.

Third, evangelize! This can be uncomfortable, but in my experience, a lot of pet owners have never thought about the question at all. My strategy was to buy Charles's person a bag of Wild Earth chow for Charles to see how he liked it.  He ate it as quickly and heartily as he ate anything else.

Fourth, about this essay and argument in particular, my estimates are crude and could use improvement. If you want to redo them, fix an assumption, or clean up my spreadsheet, I’d appreciate it!

July 2024 update

Thanks to Billy Nichols of Bryant Research, two relevant articles have come to my attention:

1. Knight (2023) estimates the number of animals killed for pet food  and their environemntal impacts. "Full transition to nutritionally-sound vegan diets would spare from slaughter the following numbers of terrestrial livestock animals annually (billions): US: dogs– 1.7, cats– 0.2, humans– 7.8, and globally: dogs– 6.0, cats– 0.9, humans– 71.3, as well as billions of aquatic animals in all dietary groups. Knight also estimates that dog diets are responsible for .57 Gt CO2-eq," vs. my estimate of about .383 gigatonnes.
2.  Domínguez-Oliva et al. (2023) perform a literature review on the health impacts of vegan diets for dogs and cats. They find little evidence of adverse effects and some evidence of benefits in the form of  "guardians’ perceptions of the diets." However, I find the claim about cats to be  implausible. If I am putting my determined skeptic hat on, the hard-to-swallow conclusion about cats is weak evidence against the article's analysis of dogs as well. However, based on my experiences with dogs, I find the idea that they can thrive on just about anything that's edible to be very plausible. An unpersuasive literature review does not move my prior very much in either direction.
    

1. ^{^}

    My intuition is that the median dog is smaller than 35 lbs, but though the smallest dogs might be 8-10 pounds, the largest are the size of small bears, so the distribution is probably skewed right.

2. ^{^}

    For context, the average American eats about 279 lbs of meat per year, (excluding fish) per year, so about 95 billion pounds/year in total for the entire country. Is it plausible that the average pet dog eats about as much meat as the average American human? I actually think so. People probably eat more calories on average but thinking about your own diet and that of people around you, you probably eat and drink a lot more processed carbohydrates, alcohol, salads, nut butters and vegetable oils, to name a few. Dogs mostly eat meat and grains.

3. ^{^}

    This essay took me about 3 hours to draft, 3 to edit, and 1 to make the accompanying spreadsheet. If I convince one person to get their dog on a vegan diet, I think it will have been time well spent.

4. ^{^}

   Ben West and  Damien Clarkson alerted me to three companies working on this: Biocraft, Bond, and The Pack.