First of all, animals should not be used for work because :im-vegan: . But having said that... I see how human labor creates surplus value. And I think I understand why machines don't create surplus value. But what about animals that get exploited to perform work, say the mule that pulls a plow? Like humans, they require a "real wage" to sustain them i.e. food, shelter, and medical attention, right? And if the value of labor power of a day of a mule is say 2 hours (that's how much human labor is invovlved in making feed, etc), then if this mule works for more than 2 hours, are they not creating surplus value for the capitalist that claims to own them?
breaking horses is one way to get a horse to take a rider but there are other ways. You can train a dog by beating them and you can make a man work by whipping them but those aren't the only ways to do so