Animals should have a happiness meter akin to what we had in the days of legacy for normal players.
They should become sad when you leave dead animals near them or kill their friends. Even having a small pen should make them sad, especially if it's overcrowded.
They should perhaps become suicidal if they see their owner killed, unless of course they were already sad in which case they might be happy the bad owner is dead, until of course they realize they are trapped forever without food now.
The happiness meter could contribute to the quality of products you get from them to some degree with sad being weight more. It could also determine their willingness to breed, eat, and otherwise desire to continue their life in their cage.