I second PD-Riverman: if the doe is really mean and isn't special for any reason (genetics, great physical features, scarcity of the breed in your area, etc.), I would probably cull her.
He may have injured his penis on the cage, ruptured a blood vessel during his attempts to breed, or scratched it some other way. Something similar happened one of my Sable bucks during breeding, and he was fine after a a day or so of rest.