Spring is right around the corner, and as a cold intolerant Georgia girl, I’m certain that I share the same (maybe a tad more) gratitude as most folks in southern Alberta for the abrupt transition to warmer temperatures. Whether you’re in the thick of your calving season or the tail end, the breeding season is on the horizon. Ensuring your bulls are reproductively sound is paramount prior to turnout with your cowherd. During the winter months, several factors such as cold stress, photoperiod, excessive or poor body condition, and reduced feed quality can contribute to poor semen quality.  The persistent extreme cold temperatures we’ve experienced this late in the year may potentially have an impact on the spermatozoa of bulls that are evaluated for breeding soundness in the upcoming months.  

Although the semen test is only a portion of the bull BSE, there are minimum semen quality requirements that must be met for a bull to pass. In this article, I will discuss the impact of cold temperatures on spermatogenesis, how that impacts the breeding soundness evaluation, and what you can do to mitigate and prevent the adverse effects of winter on your bulls’ fertility.

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How does cold weather effect semen quality?

Bulls that endure extreme cold and wind are at increased risk for scrotal frostbite that could have detrimental effects on semen quality. In a study performed in western Canada, they found that the overwhelming majority of frostbite cases occurred between January and February. They also found that the degree of severity of the frostbite correlated with semen quality.  Mild frostbite is considered 1 or 2 scabs at the base of the scrotum that are <2cm in diameter. Mild frostbite tended to have minimal effects on semen quality. However, severe frostbite was described as 1 or 2 scabs that are >2cm in diameter did have an adverse effect on semen quality. 1 Yearling bulls tend to be less affected by scrotal frostbite than mature bulls because their scrotums are not as pendulous, making the testicular blood supply less susceptible to issues associated with thermoregulation.   Frostbite causes inflammation of the scrotum leading to increased temperature of the testes, disturbing spermatogenesis. Common morphology defects associated with cold stress are distal midpieces reflex defects such as bent or folded midpieces and tails.  In the picture below, it shows the typical distal midpiece reflexes (DMRs) seen when evaluating morphology of the sperm. These defects result in a decision deferred (DD).