As anyone who weathered last year's bitter winter on the Northern Plains can attest, the negative effects of a tough winter can linger way beyond the coming of spring grass.
Those negative impacts might be of a financial nature due to expensive feed; a reduced cow herd due to death loss; or reduced cow condition that brings weak calves and poor rebreeding rates. They can also be much less obvious.
During any winter with cold and windy weather, producers need to be alert to the dangers of scrotal frostbite in bulls. Cold weather and/or wind chill can result in bull infertility the next breeding season by causing testicle damage and semen deterioration.
Duane Mickelson, DVM, a bovine reproductive specialist in the Veterinary Clinical Sciences Department at Washington State University in Pullman, says bulls need to be protected from winter winds and cold temperatures. The worst combination of elements, he says, is wind and cold.
"That's when bulls really need protection," he says. "Fertility soundness examinations should be done by your veterinarian before the coming breeding season if there is any chance that a bull's reproductive system may have been damaged by frostbite. And, any new bulls going into a herd should definitely be checked."
A Case Study In December 1964, blizzard conditions over much of the West caused serious frostbite in many herds, Mickelson says. A study done in eight states and the Canadian province of Alberta the following spring found that of 6,389 bulls examined, 14.4% had scrotal frostbite. Semen quality in those bulls was significantly inferior as well, he adds.
Defects in sperm were directly proportionate to the severity of the frostbite lesions, testicle adhesions and swelling of the testes. Older bulls, with lower hanging scrotums, were more frequently and more adversely affected than younger bulls. Mature bulls, Mickelson explains, are not as able to pull their testicles up close to the body to keep them warm. Yearling bulls were the least damaged.
Mating behavior was also adversely affected in many of the damaged bulls; some refused to service cows for six months following the blizzard. Several bulls were checked again later; those with the most damage remained permanently infertile, while others with less severe frostbite eventually recovered.
"Semen ratings are usually a good indication of whether or not a bull is damaged," Mickelson says.
The bulls with merely questionable semen quality after an initial evaluation generally have a better chance of recovery than those with obviously unsatisfactory semen, he adds. Several veterinarians in the 1965 study reported that testicle swelling was always associated with unsatisfactory semen quality.
Glen Coulter, DVM, head of the Livestock Sciences Section at the Lethbridge Research Centre in Lethbridge, Alberta, Canada, says "scrotal frostbite of bulls is a moderately common problem in cold winter climates.
"It usually occurs in bulls that don't have adequate dry bedding or protection from the wind," he says. "Minor scrotal frostbite involving areas one to two centimeters in diameter at the very bottom of the scrotum is common and generally has only a short-term detrimental effect on seminal quality."
Coulter says that the more severe the frostbite and the closer it occurs to the start of the breeding season - as in a late winter storm - the higher the probability that the bull's fertility will be impaired.
"The primary insult to testicular function occurs as a result of the heat produced by the inflammatory response, not the cold itself," he says. "Moderate to severe frostbite affecting 10-30% of the scrotal surface will necessitate a minimum of two months and perhaps as long as 12 months for recovery to restore normal fertility. That's if no adhesions occur between the testes and scrotum. If adhesions occur, the loss of normal fertility may be irreversible," he says.
Sensitive To Temperature Changes A bull's testicles are very sensitive to temperature changes. According to Cornelia Kreplin, bovine reproductive specialist with Alberta Agriculture, cold weather causes two extremes in temperature in the bull's scrotum. First, there is supercooling at the onset of frostbite.
"The second extreme is superheating as the frozen tissue thaws and inflammation occurs," she says. "Supercooling is typically short, while the superheating can last 10 days after the initial injury. Inflammation causes swelling and testicle swelling always produces lowered semen quality," she says.
Washington State's Mickelson adds that the extent and reversibility of the damage to a bull is directly related to the extent of damage within the testes. Some bulls exposed to extreme cold can suffer sperm damage even if they escape scrotal frostbite. He says that the incidence of unsatisfactory semen among bulls exposed to cold weather (even without visible evidence of frostbite) was higher than expected in the bulls that were tested in the 1965 study.
The weather conditions that caused problems that year were rain turning to ice and snow, accompanied by several days of temperatures lower than -10"degrees" F. In addition, winds were gusting up to 60 miles per hour. The wind chill factor was equivalent to about -70"degrees" F.
Bulls Can Recover Bulls can recover from scrotal frostbite, Mickelson says, if there are no adhesions in the scrotal tissue and if the sperm tract is not damaged. The lower part of the scrotum usually suffers first. This area remains unprotected when a bull draws up his testicles against his body for warmth. If there is damage to the epididymis (at the bottom of the scrotum), semen will not be viable.
After a cold winter, especially if there have been periods with wind, producers should check bulls for signs of damage. According to Kreplin, "blisters and scabs will be obvious for about three weeks after the frostbite happens. Scabs will fall off in about a month, leaving reddish-pin scar tissue."
If there is evidence of frostbite, check the extent of the injury, she says. In many cases, only the lower tip of the scrotum is affected and permanent damage to the testicles is not as likely in those cases.
If a testicle is pliable and appears normal, Mickelson says, there is a good chance the bull is not damaged. But if there has been serious freezing of the tissue, the scrotum will show signs of scarring. There will be a scabby area on the bottom third, up the back, where the scrotum has been exposed to the wind.
This kind of damage will prevent a bull from raising and lowering his testicles properly. If he can't move them up and down to compensate for temperature changes, he'll be infertile, Mickelson says, since sperm production and viability depend upon proper temperature.
Some Protective Measures Windbreaks and good bedding during bad weather can help prevent testicle freezing, Mickelson says. Bulls being trucked in cold weather should be protected, since traveling in an open truck creates a serious wind chill factor. Good bedding can provide insulation and protection since bulls won't have to bed on frozen ground exposed to the wind.
The best way to prevent cold weather damage, says Mickelson, is to make sure bulls have a place to get out of the wind. And, if there is any question about the fertility of a bull or the possibility of frostbite, have him checked by your vet.
Damaged testicles will produce abnormal sperm cells that will be obvious in a semen sample. Cornelia Kreplin of Alberta Agriculture recommends waiting at least 40 days from the initial frostbite before taking a semen sample to determine if sperm cell structure has been permanently affected. If the sperm-producing cells have degenerated or died, some of these abnormal cells will appear in the semen.