The importance of pre-breeding bull management often is highlighted as a means to prepare for a successful breeding season, says Carl Dahlen, North Dakota State University Extension Service beef cattle specialist. “However, a successful breeding season is not necessarily guaranteed once healthy bulls are turned out with a group of females.”
A breeding soundness exam (BSE) should have been conducted on bulls prior to the breeding season to identify unsatisfactory bulls, which are unlikely to sire as many calves as bulls that passed a BSE.
A BSE evaluates indicators of fertility such as semen motility and morphology. It should be performed along with an internal examination and an evaluation of physical characteristics vital to breeding success.
“A BSE does not, however, give an indication of a bull’s libido, or desire to breed,” Dahlen says. “After turnout, a simple step producers can take to evaluate libido is to watch pastures and make sure bulls are actively seeking and breeding females.”
Watching bulls also can help producers spot physical deformities (deviated penis, inability to extend penis, etc.) and other issues that can prevent successful intromission and ejaculation from occurring. 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.
In addition, keeping an eye on the bulls will help producers notice injuries that occur during the breeding season and limit the bulls’ ability to breed cows successfully. Some injuries are readily identified and others may require close observation.
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 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,” Dahlen says. “In any case, part of the healing process can create scar tissue, and this scar tissue may interfere with future reproduction.”
He suggests producers observe 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.
To get bred and become pregnant in natural-service breeding systems, females must be cyclic and stand to be bred. If producers expect that 60 to 65 per cent of females will calve within the first 21 days of the calving season in a herd of 100 cows, then a minimum of about three cows must be bred per day during the first 21 days of the breeding season.
“The number is actually slightly higher because not all matings result in a pregnancy,” Dahlen says. “If all cows are cyclic, we expect to see almost five per cent in estrus on a daily basis.”
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, Dahlen advises.