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Bull Fertility After Extreme Cold Temperatures

by Wyoming Livestock Roundup

The 2023 winter in Wyoming has been difficult for everyone, but especially for livestock producers. Winter weather and extreme cold temperatures can have significant impacts on herd performance. 

With breeding season around the corner for many Wyoming cow/calf producers, it is important to evaluate bulls and ensure their productivity hasn’t been damaged due to the harsh, cold environment.

Breeding soundness exams

Breeding soundness exams (BSE) were a developed practice, first utilized to assess bull fertility following harsh winter conditions which took place during the winter of 1948-49. 

Today, BSEs are a common and recommended practice for cattle producers every year, regardless of weather conditions. The goal of a BSE is to identify bulls with fertility issues prior to the breeding season to minimize open cows. 

It is recommended a BSE be performed on sires at least 60 days prior to the breeding season to allow ample time to replace unsatisfactory bulls or retest any bulls which suffered a cold injury prior to the breeding season.

A good BSE includes a physical exam evaluating a bull’s athleticism, mobility in the pasture, structure and body condition, in addition to scrotal circumference measurements, which are taken to predict a sire’s sperm-producing capacity.

Lastly, sperm motility and morphology are analyzed to ensure sufficient quantities of mobile, properly-shaped sperm cells are available. 

The results compiled during a BSE can be impacted dramatically by the environment the bull lives in. 


One of the most common ways a bull would fail a BSE is due to effects of a cold-weather injury and frostbite. 

Frostbite is usually visible a few days after freezing. The tissue will appear inflamed and swollen. Often a scab is present, but not always. 

In turn, the heat from the swelling or any increase in body temperature can have a negative impact on sperm cells, which are stored in the epididymis surrounding the lower end of the testicles.

Severe frostbite can eventually result in testicular degeneration and shrinking in scrotal circumference.

Frostbite can cause temporary or permanent sterility. If the damage is not too severe, it may be possible to let the bull heal and stay productive. 

However, spermatogenesis – the production of spermatozoa – requires nearly 61 days. Therefore, a follow-up BSE is recommended at least 61 days following an injury to ensure the bull will be useful.

Earlier testing could result in unreliable results and premature culling of the bull.

Preventing cold-weather injury

One of the most effective ways to prevent losses due to cold weather is to ensure bulls are being fed an adequate diet to meet their nutritional needs. Growing bulls will have higher nutrient demands as they are still growing until around three years old. 

Bulls should be managed to maintain a body condition score of five or six for optimum fertility and reproductive health. Underfed bulls are known to have greater sperm cell abnormalities and are more vulnerable to cold weather.

Harsh winter conditions, especially wind, can drastically increase a bull’s nutrient demands and his chances of testicular damage due to freezing. Protective measures such as providing shelter, a snow fence and/or bedding can be effective ways to prevent injury. 

Also, enclosing trailers for bulls being transported during cold temperatures can be helpful. 

Final thoughts

Reproductive success remains the number one economic factor for profitability in cow/calf operations. Evaluating bulls after a tough winter is especially important to ensure females are getting bred this spring. 

By paying close attention to breeding animals now, producers can ensure the negative impacts of the 2023 Wyoming winter won’t linger on.

Chance Marshall is a Fremont County University of Wyoming Extension educator. He can be reached at or 307-332-2363. 

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