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Division of Agricultural Sciences and Natural Resources

Do not mix young and old bulls in the breeding pasture

PURCELL, Okla. – With spring bull sales in full swing, cow-calf operators are assessing their bull batteries and making needed purchases; however, in most cases, producers should not place young bulls in the same breeding pasture as older, larger bulls.

 Wes Lee, McClain County Extension director and agricultural educator, reminds cow-calf producers that young bulls generally cannot compete with older bulls when it comes to deciding the dominant individual in the breeding pasture.

“In some cases, ranchers have reported cases where young bulls have been severely whipped and are less aggressive breeders after the incident, thereby negatively affecting the producer’s investment in the young bull as breeding stock,” Lee said.

Australian data on multi-sire pastures have shown that some young bulls gain a dominant role as they mature and breed a large percentage of the cows. Other young bulls never recover, gain that dominant status and only breed a very small percentage of the cows in a multi-sire pasture for the remainder of their stay at the ranch.

The best solution is to always place young bulls with young bulls and mature bulls with mature bulls in the breeding pasture. In some situations, the rancher may choose to use the mature bulls in the first two-thirds of the breeding season and then rotate in the young bulls.

“This allows the young bulls to gain one or two months of additional age and sexual maturity,” Lee said. “In addition, the young bulls should have considerably fewer cows in heat at the end of the breeding season as the mature bulls will have bred the bulk of the cows or heifers. The young bulls therefore will be in the breeding season only a few weeks and should not be as run down or in poor body condition at the conclusion of the breeding season.”

As for determining how many cows should be mated to young bulls, the old rule of thumb is to place the young bull with about as many cows as his age in months.

“A true yearling bull should be exposed to 12 or 13 females,” Lee said. “If he is 18 months of age, then he should be able to breed 15 to 18 cows. By the time the bull is two years of age, he should be able to breed 24 or 25 cows.”

Lee adds it is important to remember that tremendous variability exists between bulls. Some are capable of breeding many more cows than what is typical. Sadly, a few bulls will fail even when mated to a very few cows.

“Hopefully, a breeding soundness exam and close observation during the first part of the breeding season will identify these potential failures,” Lee said.

The McClain County Extension Office is part of the Oklahoma Cooperative Extension Service, a state agency administered by Oklahoma State University’s Division of Agricultural Sciences and Natural Resources.

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