We all know that dogs can be vegetarian but cats cannot. For cats, the amino acid taurine is essential, that is to say they cannot sythesise it, (certainly not enough) so must have it in their diet. The usual source is animal flesh. On the other hand, dogs can make their own taurine so they don’t need to eat meat.
But why the difference? I can’t find an explanation so here’s my theory.
It seems that the dog has become fully integrated into the human lifestyle and that includes food-sharing. The traditional diet of man is grains; dogs would have a share of that whereas meat was a rarity, too precious to feed to dogs. Hence the dog eventually became adapted to a meat-free diet. Probably not a coincidence, but humans make their own taurine too.
Cats on the other hand, although domesticated didn’t become fully reliant on food provided by man. They did a bit of freelancing, living off the land. After all, that’s probably why they were allowed to become companion animals in the first place – to keep vermin under control. And that is where it gets really interesting. I’ve just found out that mouse carcass has six times as much taurine as beef muscle! That high level of taurine meant that cats didn’t need to make their own. Or if they ever could, they lost the capability.
Remember, you heard it here first.