There’s actually different kinds of carnivores! Cats are hypercarnivores, which means they need more than 70% meat in their diet and can easily survive solely off of meat. Wolves and coyotes are mesocarnivores and need more than 50% meat in their diet, but need some roughage for digestion.

Dogs are hypocarnivores like bears (and so, while they are most healthy when 30% of their diet is meat, they can supplement easily with plants and survive a long time that way). Dogs can derive nutrition from grain and starches, have molars for grinding fibrous plant material, have a long small intestine that allows them to break down plant matter, and can metabolize betacarotene from plants into Vitamin A. They’re descended from mesocarnivores, but the tens of thousands of years living with omnivorous humans has lead to them developing all these semi-omnivorous traits that enable them to survive off of plants.

That said? I wouldn’t feel comfortable forcing them onto a starvation plant diet. That 30% meat requirement is still real, even if a dog could probably be kept alive for a long time on a strictly vegan diet. I think we just need to wait for lab grown stuff to supplement dog food (and that seems like it’ll happen a lot sooner than lab grown meat for humans).