Bull fertility is directly tied to herd productivity.
Bob Larson, Kansas State University veterinarian, says reproductive efficiency drives the income side of cow-calf operations.
Larson and fellow K-State veterinarian Brad White recently discussed a University of Tennessee case study on the “Bovine Science with BCI” podcast focused on breeding soundness exams.
“They evaluated nearly 1,400 bull breeding soundness exams conducted between 2008 and 2018,” Larson explains. “They came up with several factors and split them into intrinsic and extrinsic categories.”
Intrinsic factors include age, breed and history. Extrinsic challenges relate to season, nutrition and temperature.
From the exams, about 25% of the bulls failed. Not because of one single issue, but a combination of factors.
Read more about the importance of BSEs:
The Puberty Gap: Age Matters
Age plays a role on both ends of the spectrum. Older bulls have a higher failure risk, but so do yearling bulls. An important note is that yearling bulls may fail due to immaturity, not permanent infertility.
“If we test bulls around 11 months of age, there’s a fair number that will fail. But within six to eight weeks, they are maturing,” Larson says. “Age does make a difference around the yearling stage.”
Seasonal Slumps: How Heat and Forage Quality Impact Semen Counts
Seasonal challenges bring different impacts to your herd. In the cold months of winter and the heat of summer months, bull semen counts are at their lowest. The harsh elements combined with nutritional challenges influence fertility.
“Winter and summer were associated with a lower chance of passing the BSE than in the spring and fall,” Larson says. “Sometimes it’s not just the temperature, it’s the forage that’s available and quality of diet that’s available during the colder parts of the year.”
Read more about how environment and nutrition impact bull fertility:
Factors That Can Affect Bull Fertility
Context is Key: Evaluating the Whole Picture
Not all factors are equal, and neither are all failures. BSE’s are a snapshot of time. It is important to understand BSE failures versus deferred bulls.
A bull is deferred when issues are likely temporary and reversible with time or treatment, such as immaturity, sickness or an injury that can heal. In most cases, deferred bulls will improve and pass when retested.
Bulls that failed previously are six times more likely to fail again. But there can be more factors contributing to the failure of a BSE. Age at testing, time of year and environmental conditions can all have an impact.
Larson encourages producers to look at their herd circumstances and think critically about the BSE results.
“Breeding soundness exams provide valuable insight, but they should not be viewed in isolation. You’ve got to look at the context, including year, quarter of the year, age of the bull and what defects we’re seeing,” Larson says.
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