Sometimes animals are a pest. Usually the plague is the beginning of a new balance. First you have the snails, then the birds. First the mice, then the weasel. But, sometimes the plague cannot be tamed because there are no predators. Think, for example, of wild boar. In such cases, an expensive fence is necessary.
Young plants can often be protected from hares, deer or squirrels by putting netting or a tree protector around them.
Livestock is another story. Chickens, ducks, pigs and cows do not fit into a system based on no external input (as they are almost always fed extra). Moreover, territorial behaviour does not play any role and therefore, even in small numbers, they are very quickly disruptive to the soil and herb layer of a food forest.
Keeping cattle with trees is another form of agroforestry, not a food forest. If you have enough space, you can of course keep cattle next to your food forest, but not in it."