[southernplaces7]

For 2: We actively breed certain types of animals for viciousness on an industrial scale. One comment below already mentioned bulls, but certain dogs fit the bill too.

1: Where in the world did you get the idea that breeding mice isn't feasible or profitable to somebody. There's a whole relatively vast market for industrial scale breeding of small rodents that includes mice, gerbils, hamsters, guinea pigs and of course, rats. They're bred not just for food but also for all kinds of uses.

There are also even people who industrially breed the even smaller creatures that make food for small animals (and sometimes for us). Thus you have cricket breeders and breeders of all sorts of small arthropods and marine or aquatic creatures and etc. Size certainly doesn't matter much, even for food economies.

Many of the creatures I mention are indeed domesticated by now. For example, the lab rat is an actual domestic subspecies of the Norway rat and its very name implies the domestication: Rattus norvegicus domestica