The majority of beef herds in this region are in the heart of their breeding seasons, and many of those that aren’t will start their breeding seasons soon.

“From a management standpoint, the work isn’t over once breeding soundness exams are conducted and potentially fertile bulls are turned out to breeding pastures,” says Carl Dahlen, North Dakota State University Extension Service beef cattle specialist.

To ensure a successful breeding season, bulls should be monitored carefully for breeding activity, injuries and overall condition throughout their time in breeding pastures, he advises. The desire of a bull to breed, or libido, is not something that can be determined during a breeding soundness exam. In addition, breeding is a learned behavior, so producers should pay particular attention to monitoring yearling bulls.

“To monitor breeding activity, simply take the time to watch pastures and make sure bulls are actively seeking and breeding females,” Dahlen says. “While watching bulls, physical deformities (deviated penis, inability to extend penis, etc.) and other issues that can prevent successful intromission and ejaculation from occurring also can be identified. In these instances, a bull may be mounting cows in heat but not completing a successful breeding. Pay attention to the entire mating process to make sure erection, intromission and ejaculation all are occurring.”

Injuries are another major issue that can be identified while monitoring bulls. Some injuries can severely limit or eliminate a bull’s ability or desire to breed females successfully. A summary of breeding soundness exam results from North Dakota veterinarians revealed that injuries to reproductive organs were a major reason for mature bulls failing tests.

“As these injuries were identified during a breeding soundness exam and not during the breeding season, close observation is required,” Dahlen says.

Major injuries that would make bulls physically unable to perform, such as broken or sprained legs, likely would be easy to spot. Lacerations that result in a penis not being able to retract are easy to see as well. Other cases are not as easy to identify. For example, swelling just ahead of the scrotum may indicate a “broken penis” or a hematoma, and swollen or misshapen testicles may indicate testicular injuries.

Injuries may cause physical pain and a low libido, or a bull may be willing to breed but is no longer capable. In any case, part of the healing process can create scar tissue, and this scar tissue may interfere with future reproduction.

Dahlen recommends observing bulls interacting with females and females interacting with each other early in the breeding season because those interactions can give a good indication of the relative proportion of females that are cyclic.

If all cows are cyclic, producers should expect to see almost 5 percent in estrus on a daily basis. Fewer and fewer females will be in estrus on a daily basis from the middle to the end of the breeding season.

So if 65 percent of the cows became pregnant in the first 21 days, then only 35 percent of the herd remains to be bred. This means less than 2 percent of cows would be in estrus per day from day 22 to 42 of the breeding season. After day 42 of the breeding season, less than 1 percent of females should be in estrus every other day for the remainder of the breeding season.

Ideally, cows should be on an increasing plane of nutrition with sufficient supplies of mineral and high-quality pastures or feeds during the breeding season. If close observation of pastures reveals that a relatively similar proportion of cows are in estrus in the middle of the breeding season, compared with early in the breeding season, then some type of intervention is critical.

Once bulls have been evaluated for injuries, body condition and libido, and single-sire pasture bulls have been evaluated for the ability to mate successfully, producers should take active steps to rotate or replace bulls that are injured, have low libido or are in pastures with a high proportion of estrus cows late in the breeding season.

“Identifying potential issues before the end of the breeding season can allow a producer to take active steps to salvage the remainder of the breeding season and ensure a greater proportion of the herd becomes pregnant,” Dahlen says.

For more information, contact Dahlen at (701) 231-5588 or carl.dahlen@ndsu.edu, or NDSU Extension veterinarian and livestock stewardship specialist Gerald Stokka at (701) 231-5082 or gerald.stokka@ndsu.edu.

NDSU Agriculture Communication - July 9, 2015