At what age do Jersey bull's temperaments start changing? We have several Jersey cows and not being able to find a bull to borrow or a vet to do AI, we bought a bull last year. He is now 3 years old or so. We've bred him already and will be moving him down here from a friend's house this week. I'm wondering about when they change because thus far he has been the quietest most laid back bull I have ever seen, although we absolutely never take him for granted, take unnecessary risks or even go in with him if it can be helped, but I said the day he starts changing is the day he goes in the freezer. But I was kind of wanting to know about what age they start changing? I said as long as his temperament holds, I'll keep him, but I do watch him very carefully and I never allow the kids near him at all. We take the same precautions with him that we do with the pigs for safety's sake. I don't trust him at all. But thus far he has not given us a lick of trouble. Any guesses on age that I need to think about getting rid of him?