After spending 35+ years in the artifical insemenation business, I can tell you removing the testes after death is done all the time to the really great bulls. I think collecting semen from a cape buffalo with huge horns like his would not only be difficult but close to impossible. getting him into a collection chute would be impossible. As I see it the only way it could be done is to dart him with a tranqulizer and use a "electro ejaculator" on him while his is out. There is just no way to confine an animal like that, without the collector putting his life in jeoparday. Bulls in AI have there horns removed for the saftey of the people handling them, then they put a ring in the nose and two lead ropes. A person one each side will lead him to a female in season or a collection dummy, when the bull starts to mount the collector moves in and redirects the penis (with his hand) into an artifical vagina. Not something I'd be willing to do with a cape buffalo, and I've collected my share of bulls.
Bob