When Spot turns up pregnant by one of 12 male cats aboard Enterprise, that suggests that cats and other creatures roam the ship at will, or that Spot went to at least one kitty playdate. Aside from the whole "animals shouldn't be enslaved by people" thing, wouldn't that cause lots of problems for the running of the ship? You can give people warnings about their own behavior, but pets couldn't be held responsible for their own conduct. You could warn the owners of the pets about keeping their animals under guard, of course. Is there some kind of force field that restricts pet animals' access to places people crew can go?