Scrotal frostbite in bulls can impair fertility
January 11, 2019
Cold, windy weather can result in bull infertility the next breeding season. Scrotal frostbite can temporarily or permanently affect fertility, depending upon severity of freezing — causing testicle damage and semen deterioration.
Duane Mickelsen DVM, a cattle breeder near Pullman, Wash., (retired from Washington State University), has been doing fertility studies in beef cattle for many years, and thousands of breeding soundness exams on bulls. Though his region generally doesn't have severe winters, there have been a few years when cold temperatures and wind resulted in problems. He recalls one severely affected bull in which testicular damage resulted in a dramatic difference in scrotal circumference. "He went from about 37.5 centimeters down to 31.5 and scarring on his scrotum was severe," Mickelsen said. "Wind, along with cold, can make the problem much worse. It usually damages the testicles, causing testicular degeneration and inflammation. I usually look bulls over very closely in the spring, following a cold winter. If we see a scab at the bottom of the testicle, this is a clue that there has been some damage."
George Perry, PhD, professor and beef reproduction specialist at South Dakota State University, said spermatogenesis (creation of sperm) in a bull is 61 days. "Anything that affects sperm production will take 61 days to totally clear the system, to have normal cells and healthy sperm again after the bull recovers," he said. If frostbite was severe it may take several months for full recovery, and a few bulls remain permanently infertile.
"A few years ago we checked one bull that had frostbite in February, and by June he was fine," Perry said. "Where the sperm happen to be in the production cycle can make a difference in what will happen to the sperm when frostbite occurs. We've seen different problems occur in the heads or tails of sperm, but this will all affect the bull's fertility."
IMPACT ON FERTILITY
"You can see the scabs that form after frostbite damage to the scrotum. Even when the scabs are gone and the skin heals, there can be residual affects on fertility due to misshapen or deformed sperm for the entire 61 days following recovery. Any of those problems will have a big impact on fertility. We have to give those bulls enough time after they are completely healed, to make sure they are producing good sperm before we turn them out with cows," he said.
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Mickelsen said that it takes 48 days to create the sperm in the testicles, then the sperm spends 10 to 12 days in the epididymis maturing, before going into storage to be ejaculated. "If there is scrotal damage, what you see when you examine the semen is a tremendous increase in primary abnormalities — head defects and proximal droplets (on the mid-piece right underneath the head of the sperm). The bull I mentioned — whose testicles shrank in size — had 90 percent abnormal sperm two months after the frostbite incident," he said. He still had not recovered.
"Sometimes in the spring if there's a cold snap with a strong wind — and maybe a little snow and wind — the bull may suffer damage, though not as severe as deep freezing. There may just be an increase in secondary abnormalities in the sperm — bent tails, and some droplets down on the mid-piece. But this will clear up in about 10 to 14 days because this has only affected the sperm in the epididymis (which is right on the surface) and not in the testicles. After new semen moves in, the bull is OK; the infertility is very temporary. But scrotal frostbite can cause permanent damage," he said.
"Some of these bulls can recover. This is why I like to palpate, semen test and check them about two months later. If you know when the cold weather hit, you can check them long enough afterward to know if they still have a problem. If they are still bad, you need to cull that bull," Mickelsen said.
Anything that interferes with temperature regulation in the scrotum can affect bull fertility. "We see similar problems if the scrotum gets too hot in the summer, which can happen when there's too much fat build-up in the scrotum," Perry said. The excess fat serves as insulation and hinders the bull's ability to keep the testes at proper temperature. For healthy sperm production the testicles must be a few degrees below body temperature.
A bull lowers his testicles in hot weather, and draws them up closer to the body in cold weather to keep them warm. Severe scarring from scrotal frostbite may interfere with raising and lowering the testicles, interfering with proper temperature regulation.
"Anything that affects the neck of the scrotum also affects the countercurrent exchange for temperature," Perry said. "This is a sensitive area, and if there is frostbite on the neck of the scrotum the bull may not be able to drop or contract the scrotum enough to properly control temperature," he said. This can have a negative effect on fertility.
"During winter a lot of producers don't provide bedding for bulls — or don't bed them well enough to avoid frostbite. The scrotum has very little protection compared with the rest of the body. It's basically bare skin with just a fine hair covering. If bulls lie on frozen ground or snow, they are basically putting the testes on ice." If it's windy, the testicles are exposed to wind chill. Bedding can provide insulation.
Cattle stand with their backs to the wind, and the older bulls with pendulous scrotums and low-hanging testicles may not be able to pull them up as closely to the body for warmth — and suffer frostbite on the bottom and backside of the testicles. "Horses and cattle bunch together for warmth and protect one another from the wind," Mickelsen said. "I've seen a lone cow or horse die in cold weather because they lose too much body heat and get too cold to survive said. If the whole body is getting cold, you can certainly understand how the testicles could suffer damage."
Perry said the term frostbite implies minor frost damage, but with a lot of wind in cold weather, the tissues may suffer severe freeze damage. "Stockmen need to realize how long it takes to recover. Even when you can no longer see scabs, and the skin has healed, that's when normal sperm production resumes, and the time starts for the 61-day period before the healthy sperm is mature and the bull is fertile again," Perry. said. Bulls with severe damage may not be fertile until late summer.
This is a good reason to perform breeding soundness exams each year, before you turn the bulls out with cows. Just because a bull was fine last year doesn't mean he will be fertile this year. Some people simply check new bulls going into the herd and don't check the older bulls.
A good bull is a major investment and you want to take care of that animal, with windbreaks and bedding. It's also important to check all bulls before the next breeding season.
I've gone into some herds where the last thing the owner wants to do is spend money on testing the bulls the next spring," Mickelsen said. "I have some purebred breeder clients who always semen check the young bulls they plan to sell, but don't check the old herd sires. They just assume they will be OK from year to year. But there can be problems with older bulls."
"In commercial herds I recommend not keeping bulls past 4 or 5 years of age. If it's a valuable bull, however, many people continue using him for a long time. Those older bulls do need to be checked," Mickelsen said.
After suffering frostbite, if the bull doesn't have normal sperm at the time he's checked, the producer might give him another 60 days and check him again. ❖
— Smith Thomas is a cattle rancher, horseman, freelance writer and book author, ranching with her husband near Salmon, Idaho. She can be reached at firstname.lastname@example.org.