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(March 18th)

Commercial Heifers

Reproductive Success Starts with the Bull

Annual breeding soundness exams key to overall herd fertility

by Lisa Bryant, Communications Specialist

Buying health insurance is not a fun task, but it’s a necessity to mitigate your risk in case of a major health event. Increasing your herd’s reproductive performance presents a similar scenario. Testing all your bulls before breeding season is a simple task that can help prevent a major blow to your wallet.

“Passing a breeding soundness exam is insurance for the owner,” said Barry Whitworth, DVM, and senior Extension specialist in the Oklahoma State University Department of Animal and Food Sciences. “All bulls should be tested annually to make sure they’re good.”

An untested, sterile bull can be costly if several open cows turn up, he said. Smaller producers with only one bull are at higher risk, but Whitworth warned that ranchers running five or six bulls in a pasture can also have issues if one bull is sterile. “If he’s the biggest, baddest guy out there, he’s going to keep everybody beat off and you’re still going to have lower pregnancy rates.”

Whitworth said sub-fertile bulls will eventually get cows bred, but not in a desirable timeframe like a bull that passes a BSE.

“You’re going to have more cows that get bred later in the breeding season and calves born later in the calving season,” he said.

“At weaning time, there will be more lightweight calves compared to the cows that bred and calved early in the season. You’re just losing pounds.”

Research shows that bulls that pass a BSE get cows bred earlier in the breeding cycle and they have a higher success rate of settling, Whitworth said. “You don’t tend to see repeat breeders that may breed and conceive, but 30 days later, she’s breeding right back. That means you’re going to have more calves born at the first of the calving season, which should correspond with higher weaning weights at the end of the year.

“A bull should get about 60% of the herd bred in the first 21 days. Within 45 days, 98% of all cows should be bred.” He added that it’s economically important to get all cows bred in the first three breeding cycles.

Age doesn’t matter when it comes to the importance of performing a BSE on bulls, Whitworth said. However, the “why” to test may vary for different ages of bulls.

It’s not unusual for a young bull to fail the exam initially, especially if he’s been over conditioned, he continued.

Barry Whitworth, DVM

“A lot of our young bulls, especially if they’ve been fed a lot, will get a deferred rating the first time because they are so fat.”

Too much fat in the scrotum causes an inability for temperature regulation. This leads to motility and morphology abnormalities in the sperm cells.

Whitworth said we can often fix this by letting the bull lose weight or by getting him out in the field where he can travel and increase exercise.

On the flip side, older bulls are more likely to fail because of an infection or injury.

Extreme weather events in regions not accustomed to that type of weather can also temporarily affect a bull’s sperm. Whitworth said frostbite or extreme heat can damage the testicles, and the severity of the damage may influence recovery time.