As spring calving season begins to wrap up, it’s time to start thinking about breeding season and making sure bulls are ready for work.
Saulo Zoca, University of Tennessee assistant professor and beef cattle reproduction specialist, reminds producers the importance of performing breeding soundness exams (BSEs) 30 to 60 days before breeding season.
Zoca shares these factors that can affect bull fertility and ability to get cows bred.
Injury
Injuries like hematomas, broken penis or broken legs can impact a bull’s ability to breed cows.
Disease
Reproductive diseases like Trichomoniasis, Campylobacter, and Vibrio can negatively impact bull fertility.
Temperature stress
Heat and cold stress can both affect fertility. Heat stress decrease sperm motility and increase morphological abnormalities in sperm. Zoca explains that the testes need to be 2 to 3 degrees cooler than body temperature for normal sperm production. He also said in cold environments, bulls can experience frostbite on their scrotum, which can impair the testes’ ability to thermoregulate.
Zoca adds that humidity can play a role as well, as higher humidity makes it harder for the bull to dissipate heat through sweating and evaporation. “The combination of heat and high humidity can be particularly challenging for bulls,” he says.
A study at Virginia Tech demonstrated that heat stress caused a significant decrease in sperm morphology, while sperm motility remained above the minimum threshold for several weeks after the heat stress event.
The key is managing a bull’s environment, whether that’s providing shade, wind breaks, bedding or other methods to help them thermoregulate and avoid the negative impacts of extreme temperatures and humidity on their fertility.
Semen quality
Zoca emphasized the importance of semen quality, particularly sperm morphology, in determining a bull’s fertility potential.
Over conditioning
Feeding bulls to gain more than 4 lb. per day can lead to increased fat deposition, insulin resistance and inflammation, which can impair sperm quality and fertility. Over conditioning can impact both young and mature bulls. Experimental studies showed that bulls with higher subcutaneous fat deposition had a greater percentage of sperm with abnormalities.
Nutrition during early life
Proper nutrition during the first 6 months of a bull’s life can influence when they reach puberty and their later fertility.
