Big difference between dogs and fish. Fish can’t even recognize you; dogs give unconditional love. Not as big, but there’s a big difference between cattle and horses, too.
A pet, is a pet, be it a fish or an elephant. Telling a child that their pet fish is dead and telling a child their pet dog is dead amounts to the same thing.
As for differences between a cow and a horse ... cows, in general, are not cute, horses are, therefore we have no problems eating a cow, but a horse is different.
In our culture horses and dogs are considered pets therefore we have problems with the idea of using them for food ... not so in many cultures worldwide.
Having had the occasion to live in a Montinyard village back in the day, food was food and dog was food just like chicken was in our country. However, I will admit, the animals were dead before skinning.