Most labs breed their own lines so that they can keep a consistent gene pool for their studies. In doing this, there is no extraneous variable with a different line of animal. If they do not breed...
Animals eat other animals because they are carnivors, herbavors eat just palnts/crops and omlivors eat both aniamls and plants/crops. But we can't help it because it's passed down from mother to baby...
More animals. The question is far too broad. Many things come from animals. From food to clothing. Drugs and knowledge. Companionship from pets. A plethora of useful things.