As the breeding season approaches for many producers, bull readiness is critical to ensure reproductive success. With the majority of U.S. beef cows bred by natural service, bull fertility has a direct impact on pregnancy rates, calving distribution and overall herd profitability. Preparing bulls ahead of turnout can help minimize reproductive risk and protect the genetic and economic investment producers make in herd sires.  

Think 60 Days Ahead 

Spermatogenesis, the production of sperm, is a 61-day process in bulls; therefore, it will take upwards of 60 days to have normal sperm again following an injury/insult.  Factors that can decrease sperm production are disease, fever, injury, and extreme environmental conditions. Therefore, it is important to monitor and identify if a bull has experienced frost bite, or any other injury to the scrotum/testis. Identifying issues early provides time for recovery or alternative management before turnout.  

Breeding Soundness Exams: Timing and Expectations 

Conducting a Breeding Soundness Examination (BSE) approximately 4 to 6 weeks before turnout is strongly encouraged. This timing allows producers to retest or find a replacement bull.  

During a BSE, a veterinarian evaluates:  

• Physical examination which includes a scrotal circumference measurement, foot and claw condition, and mobility scores 
• Semen quality for motility and morphology  
• Rectal exam to evaluate accessory sex glands 
• Examination of prepuce and penis for adhesions, warts, or scaring of tissues 
• Testing for venereal diseases such as Trichomoniasis 

To successfully complete a BSE, a bull must have at least 30% sperm motility, 70% normal sperm morphology, and a minimum scrotal circumference based on age. Bulls meeting these minimum requirements are classified as satisfactory potential breeders. If a bull does not pass one of these tests, he is either classified as deferred (meaning it is recommended that the bull be tested again) or as an unsatisfactory potential breeder.  

Value of a BSE: Does It Pay?  

The cost of a BSE is minor compared to the potential economic loss from reduced pregnancy rates, extended calving seasons, and open cows. A single subfertile or dominant bull could have a large impact on your breeding group if you are unaware of their breeding potential. Additional information on the economic value of a BSE can be found in a past BeefWatch article: How Valu-Bull are Breeding Soundness Exams.  

Considerations Beyond a Breeding Soundness Exam 

While a BSE is an essential tool, it does not evaluate all factors influencing reproductive success.  

Bull to Cow Ratio 

Bull to cow ratio refers to the number of cows a bull can successfully breed, with national averages of approximately 25 cows per mature bull and 15 cows per yearling bull. While some operations use higher bull‑to‑cow ratios, excessively high stocking rates can increase the risk of missed heats and later‑calving cows, particularly when estrus is concentrated or terrain limits bull movement. 

Bull Libido and Effectiveness in Breeding 

Bull libido, or willingness to breed, cannot be evaluated during a BSE and must be assessed once bulls are exposed to females in estrus. Bulls may pass all components of a BSE yet fail to actively breed cows, making early observation of breeding activity critical to identifying and correcting problems before they result in open cows. Physiologically, bulls may have high libido, but due to physical injury, structural, or behavioral issues, be unable to breed cows.  

Social Behavior  

Bull social behavior also influences reproductive performance under natural service conditions, due to the social ranking of bulls within the herd hierarchy. Dominance is expressed more strongly in older bulls (i.e. 3 to 4 years of age and older) and is more related to seniority than any other factor. We may see the effects of dominance having greater impacts when we have lower bull to female ratios and limited estrus activity within a herd. Keep in mind that dominant bulls may impregnate more cows and therefore, subordinate bulls may have limited reproductive performance and fewer calves. Conversely, if dominance is associated with low semen quality or low sex drive, then herd fertility may be compromised. 

Putting it All Together 

Semen quality of an individual bull will change, and periodically evaluating a bull’s mating ability and libido should be considered. Consult with your local veterinarian about performing breeding soundness exams in your herd bulls. Herd bulls have a large influence on many aspects of an operation including profitability, calf crop, and genetic improvement. With 90% of beef cows in the United States bred by natural service, managing bulls to optimize breeding performance is important.