It seems that animals' eating requires them to be loaded, so if you're trying to breed animals, they have remain loaded while you're tempting them with food. This means your farms should be close enough to your living/working area at least long enough for them to consume all the food they need.
If I drop food for them in a trough and tear off to another part of the world expecting them to have bred in my absence, then when I return there's just a pile of food left in the trough (or sometimes a pile of rot). Once they're pregnant, though, then the rest of the process seems to be on the calendar.