This is not much request for creating mod as request for "finding one", because I cannot.
Long time ago, I saw mod, which promised to do this: you just throw some(or several stacks, doesn't matter) potatoes (or some food), and pigs (or corresponding animal) would come to it and "eat" it, then reproduce as usual. Basically, instead you feeding animals, they would feed themselves. Does anyone know, where to find this mod?
If it doesn't exist, it might be decent idea to create it. However, I'm not sure, if it would be possible. If MC does give you enough data for this.
It might be stepped up by introducing animal feeding block. Just like dispensed, but animals, if they could breed, would come to it, and take food from it. Not the young ones (or configurable how fast they can take food). This would prevent situation, when you have floor made of hoppers, for egg auto collecting, but you want about feed chickens.
Overpopulation, I hear you say. If mismanaged, this is where it would lead to, yes. But to be honest, you can overpopulate already, it's not that hard.
It would not give you any exp, since there would probably be no way of doing that, and it would be consistent with the overall concept of automatic <anything> giving you no exp.