The importance of pre-breeding bull management often is highlighted as a means to prepare for a successful breeding season. However, a successful breeding season is not necessarily guaranteed once healthy bulls are turned out with a group of females.

Prior to the breeding season, performing a breeding soundness exam (BSE) on bulls is a good way to identify unsatisfactory bulls, which are unlikely to sire as many calves as bulls that pass a BSE. A BSE evaluates semen, and, along with an internal examination and an evaluation of physical characteristics, is vital to breeding success.

A BSE does not, however, give an indication of a bull’s libido, or desire to breed. 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.

What else can watching the bulls tell us?
Physical deformities (deviated penis, inability to extend penis, etc.) and other issues 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.

Injuries that occur during the breeding season and limit the ability of bulls to breed cows successfully are not uncommon. Some injuries are readily identified and others may require close observation. Major injuries that would make bulls physically unable to perform (broken or sprained legs, etc.) likely would be readily identified. In addition, some cases of lacerations will result in a penis that is not able to retract and, therefore, be easily observed.


Other cases are not as easy to identify. A “broken penis” or a hematoma may be seen as swelling just ahead of the scrotum. Testicular injuries may be identified as swollen of misshapen testicles. 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.

What can watching the cows tell us?
Observing bulls interacting with females and females interacting with each other early in the breeding season 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 we expect that 60 to 65 percent of females will calve within the first 21 days of the calving season in a herd of 100 cows, then a minimum of just more than three cows per day must be bred during the first 21 days of the breeding season (65 cows/21 days in the estrous cycle = 3.1 cows per day, or 3.1 percent of the herd). The number is actually slightly higher because not all matings result in a pregnancy; if all cows are cyclic, we expect to see almost 5 percent in estrus on a daily basis (100 cows/21 days in the estrous cycle = 4.8 cows per day, or 4.8 percent of the herd).

As we move from the beginning of the breeding season to the middle or the end, we anticipate fewer and fewer females to be in estrus on a daily basis. 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 that we would expect to see fewer than two cows in estrus per day in a herd of 100 cows from day 22 to 42 of the breeding season (35 cows/21 days in the estrous cycle = 1.7 cows per day, or 1.7 percent of the herd). After day 42 of the breeding season, we would only expect to see a female in estrus every other day for the remainder of 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. Check that cows are in acceptable body condition (should have been increasing up to this point, have mineral and have access to sufficient high-quality feed resources).

Evaluate bulls for a variety of injuries listed above, evaluate the body condition of the bulls, and evaluate libido and ability of single-sire pasture bulls to mate successfully. 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.

Although not all problems will be seen immediately (such as the case with changes in semen quality after the yearly BSE), identifying issues before the end of the breeding season will allow time to replace bulls that need to be replaced and salvage the remainder of the breeding season. Intervention during the middle and end of the breeding season likely will result in more late-calving cows than anticipated, but the alternative is to have a much greater proportion of nonpregnant cows than anticipated. end mark

Carl Dahlen is an extension beef cattle specialist for North Dakota State University. This originally appeared in The Ranch Hand e-newsletter.

Observing bulls interacting with females and early in the breeding season indicates the relative proportion of females that are cyclic. Staff photo.