The development of sperm cells in bulls depends on several factors. A key factor is temperature regulation of the testes. Bovine testes must be maintained at a temperature around 90 F. This means that bull testes are kept around 7 to 11 degrees F below normal body temperature. Any insult to the scrotum that damages the testes and/or impairs their ability to move freely within the scrotum will disrupt temperature regulation of the testes. This will result in improper development of the sperm cells.
Damage to the bull’s scrotum may occur in a variety of ways. One way is frostbite. In a study performed in Canada, severe frostbite was associated with reduced satisfactory bull breeding soundness exams (BSE). The authors of the study suggest that frostbite resulted in inflammation to the testes, which increases testicular temperature.
Frostbite is not a common problem with bulls in Oklahoma; however, Oklahoma cattle are not accustomed to the extreme temperatures seen during the winter storm in late January. Without proper protection, bulls may have suffered damage to their scrotums or testes. Damage to these tissues may result in poor semen quality.
The wildfires that burned over 300,000 acres in northwest Oklahoma may have resulted in some hidden reproductive consequences for bulls. Minor thermal injury or burns to the scrotum might be severe enough to interfere with scrotal temperature regulation. Again, this may result in nonmotile sperm and/or abnormal sperm.
With this information in mind, cattle producers need to have their bulls evaluated before spring turnout. A BSE performed by a veterinarian should alleviate any concerns about infertility. The exam has three parts. Part one is a physical examination to ensure that the bull is in good health. Bulls impacted by wildfires may have sustained injuries to their feet which would impair their ability to breed.
Part two is the examination of the internal and external reproductive organs. During this part of the process, the scrotum will be measured and evaluated for any abnormalities such as frostbite or burns. Lastly, the semen will be evaluated for motility and morphology (normal and abnormal sperm). Any abnormalities in any part of the exam are cause for concern.
Bulls meeting the minimal standards for each part of the BSE will be classified as a “satisfactory potential breeder.” Any issues discovered will result in a bull being classified as “deferred” or “unsatisfactory potential breeder.”
Bulls with signs of frostbite or burn damage to their scrotum and with poor semen will most likely be classified as “deferred.” The evaluator will probably suggest a recheck in a few weeks. One study indicated that most problems improve after six weeks of rest; however, according to the study in Canada, the fertility of some bulls with frostbite damage never improves.
A BSE does not detect infectious diseases that might be present in the bull. These diseases may cause infertility or other reproductive problems. Testing for diseases such as trichomoniasis or persistently infected bovine virus diarrhea might prevent unwanted infections in the cow herd. If bulls were commingled with other cattle during the wildfire, producers may want to test for these diseases.
A BSE is just one step in preparing for the spring breeding season. Hopefully, it will prevent any unwanted surprises during pregnancy testing this fall. For more information about BSEs and issues associated with frostbite and burn injuries, producers should consult their local veterinarian and/or county agriculture educator. — Barry Whitworth, DVM, Oklahoma State University senior extension specialist
