Bull Condition for Optimal Fertility
For optimal fertility, bulls should never be fat.
Weight and body condition are important factors in whether a bull will be a good breeder. He needs proper fitness to be athletic, with the endurance to cover a lot of territory and breed a lot of cows.
“For a long time, I told producers that they needed to have bulls in abundant flesh because they would lose weight during the breeding season and needed some reserve. Then I saw an interesting study that was done in Canada, in some large community breeding pastures,” says Dee Whittier, professor of large-animal clinical sciences at Virginia Tech.
The research was done by Glenn Coulter, who earlier measured the fat in bulls’ scrotums and found that fat bulls are less fertile because fat insulates the testicles and keeps them too warm for optimum sperm production, and also hinders the bulls’ ability to raise and lower the testicles to keep them at proper temperature. “In this particular study on community pastures, all they did was check backfat using ultrasound. Then they turned out 30 to 50 bulls in each pasture. They blood-typed the bull, cows and calves to tell which bulls sired which calves,” explains Whittier. This way they could tell how many calves each bull sired.
He adds, “If you’d have asked me what was going to happen, I would have predicted that the really thin bulls wouldn’t breed very many cows and the really fat bulls wouldn’t breed very many, and that you’d want bulls to be in the middle. It turned out that none of those bulls were too thin to breed cows. The ones with zero backfat went out and bred the most cows. Now we realize there’s a lot more danger in making a bull too fat than in having him too thin.”
A fat bull is not as athletically fit, and he’s more likely to hurt himself, just like an overweight, out-of-shape human who tries to exercise.
“The fat bull is not very athletic, and more apt to be lazy. I think body score 5 (with 1 being emaciated and 9 being obese) is fine for a bull; he doesn’t need to be any fatter than that. A BCS 5 bull isn’t pretty (he’s in his ‘working clothes’), but he will settle more cows than the fat bull. It is crucial that these bulls not be overly fat,” says Whittier.
A yearling bull that’s still growing may run himself ragged during his first breeding season and lose too much weight for his own health, though. It’s important to give a yearling bull fewer cows or shorter turnout time, bringing him back in and giving him a rest before he loses too much body condition. It is important to monitor and manage bulls.
Having young bulls too fat when they go out to breed cows is not healthy for them and may limit their ability to breed an optimum number of cows, according to Whittier.
Editor’s Note: Heather Smith Thomas is a freelance writer and cattlewomen from Salmon, Idaho.