We are all aware of the environmental impact of the livestock consumed globally. And many suggest that a plant-based diet is more healthful for humans. But what are the environmental “paw prints” on society’s freeloaders, the dogs and cats? A new study considers the advantages of making them pursue a vegan diet.
Let's mention a few pertinent limitations before getting too deep into the subject. First, despite the significant amount of work and thought that went into this study, it is, at best, a model and, to a large degree, an exercise in Mathmagic – lots of estimates and assumptions.
“It is beyond the scope of this study to examine the nutritional suitability of vegan diets (which exclude any animal products) for dogs and cats.”
Second, it concerns itself only with environmental impacts. The nutritional value of a vegan diet for carnivores (that would be the cats) is unknown. As any owner will tell you, dogs are like us: omnivores, so with a few supplements, a vegan diet will sustain them.
To create their model, the researchers had to estimate dog and cat populations, daily calorie expenditure, and their current diet’s animal-sourced components. They then had to calculate those animal parts' environmental impact and compare it to a strictly plant-based vegan diet. The researchers' model considered US and global estimates, but I will share only the US ones at the risk of inducing number fatigue.
- The U.S. population of pet dogs is estimated at 86.3 million pet cats at 61.1 million, and that does not include feral cats and dogs. There are about 325 million humans.
- Based on studies of animal weight, the daily maintenance energy requirement for dogs is 1350 calories, for cats, 221 calories. (Humans need 2,500 daily calories for males and 2,000 for females.)
- Dog and cat food contains both animal and plant-sourced foods. For their diet, animal-sourced foods can be further broken down into those humans might willingly consume and those we avoid, animal by-products (ABP), like organs, feet, ears, skin, and bones. 
- Canine diets contain 34% animal-derived foods; felines 31%; humans eat less animal-derived foods by percentage at 18%, but our numbers mean total animal consumption is greater for humans. Cats and dogs contribute about 4% of the total animal consumption in the US.
“ABPs and their derivatives are used within pet food as protein sources, because they’re considerably cheaper than HC ingredients such as meat. This is not done to ‘recycle’ produce that would otherwise be wasted.”
- 52% of canine diets include non-human consumables, 50% for felines. These include bone meal and chicken by-product meal. So, an argument might be made that our pets are eating “meat,” just not the parts we want, the leftovers destined to be wasted. Animal by-products are, in fact, already used in a variety of other applications, from high-end foods such as foie gras to protein hydrolysates used to fortify foods with proteins and a range of industrial products from cosmetics to medical materials and clothing.
- The bottom line, 20% of livestock is used in some form to feed our cats and dogs. Like their owners, they consume a great deal of meat. Globally, cats and dogs consume 8% of all livestock.
If we were to place our pets on a solely vegan diet if for no other reason than it would be their contribution to the war on climate change (and it is easier to move them to an all-vegan diet than ourselves), we would save
- 6.6 million bovine animals, 26 million pigs, 1.9 billion poultry, and a half million or so sheep and goats.
- A 17% reduction in land use, a 6% reduction in freshwater use, and a 15% reduction in greenhouse gases.
- According to the researchers ' calculations, the energy savings of a vegan diet for our pets could feed 25% of our population, 87.5 million Americans, presumably all on a vegan diet.
- For those so inclined, rather than feed more humans with these savings, we could increase the number of cats and dogs by about 50%.
There are other sources of the cats’ and dogs’ environmental paw print, including water use, nitrogenous wastes, and housing. But to do their “fair share,” we might begin with their diet. And by the way, as the researchers point out, at least for the dogs (and we think it may also be true for the cats), those waistlines aren’t getting smaller; they too are participating in America’s obesity trends.
“Great benefits for environmental sustainability can be realised through the use of nutritionally sound vegan diets for dogs and cats, as well as for people.”
Pet Food Wars
Of course, what is nutritionally sound seems to be a bit of a puzzle for our pets and us. As any TV viewer may note, the war against “kibble” has been underway for several years. There is even a film promoting a more “natural” raw diet, PET FOOLED, and going after the evils of BIG Pet Food. The FDA controls the labeling of pet foods, and here is a fun fact: only pet foods labeled as cat or dog food must contain 95% or more meat. Using the phrase “with beef” can reduce the amount to 3%, and “salmon flavored” means your poor cat will get the taste but not the substance.
We have much more in common, food-wise, with our pets. Only during the Industrial Revolution did we see pet food move away from table scraps. Canned pet food was introduced in the 1920s and was “disrupted” by World War II, when pets joined the war as their food was, like ours, rationed. (This, of course, creates a precedent for cats and dogs going vegan to save the planet). This led to the rise of extruded, dare I say, processed pet foods that come in a bag. Over the last few years, we have seen pet food advertising change. Today, we see a return to “fresh, whole food. As The Atlantic points out, in our “humanization” of our pets,
“One of the main things that we’ve seen in the past five-plus years is that the parents, the shoppers, of the pets, they’re looking at pet food in the very same way they’re looking at the food they buy for themselves.”
So perhaps those researchers are correct, and pets will lead us all to follow a plant-based diet. Of course, it is unlikely that even in recruiting our pets, we will “eat our way” out of Earth's changing climate.
 Human consumption of these animal “by-products” has a cultural component that makes the line between human and non-human consumption, as much of the numbers in the study, a bit fuzzy.
Source: The relative benefits for environmental sustainability of vegan diets for dogs, cats and people https://doi.org/10.1371/journal.pone.0291791