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Cold weather can result
in bull infertility the next breeding season, as stockmen
discovered after the February 1989 “Siberian Express” (5 days of
cold weather with strong winds), and again in some western and
plains areas after storms in 1995-96 and 1996-97. During any
winter with windy, cold weather, stockmen should be alert to the
danger of scrotal frostbite in bulls. Cold weather and/or wind
chill can cause testicle damage and semen deterioration, according
to Dr. Duane Mickelson (bovine reproductive specialist, Veterinary
Clinical Sciences Department at Washington State University,
Pullman WA). Bulls need to be protected from winter winds and cold
temperatures.
Dr. Mickelson says
the worst weather is windy cold. He pointed out that the winter of
1995-96 was cold in some regions, but not very windy, and there
were only a few cases of scrotal frostbite reported in bulls. In
his own herd of cattle, for instance, he had frozen ears and tails
on baby calves when temperatures got down to 25 below zero F. but
no problems with the bulls because there wasn’t any wind during
those coldest periods. “By contrast, there were many bulls around
the country that ended up sterile in the spring of 1989, following
the severe wind chill during the Siberian Express that first week
in February,” he said.
The weather to watch
out for, according to Mickelson, is when temperatures drop below
zero F. accompanied by wind. That’s when bulls need protection.
Fertility soundness examinations should be done before the next
breeding season if there is any chance that a bull’s reproductive
system may have been damaged by frostbite. Any new bulls going
into a herd should be checked.
The first study on cold weather problems in bulls was done in
Wyoming in l949. After a severe blizzard that winter, ranchers
became worried because scrotal frostbite was observed in a large
number of bulls. Semen samples from 88 bulls were collected by two
veterinarians. The testicles and epididymis from three bulls that
died in the blizzard, were submitted to the Armed Forces Institute
of Pathology for evaluation. Two of those bulls had severe atrophy
of the tubes that convey semen, along with a great deal of
swelling and damage from the frostbite.
Of the 88 live bulls
tested for semen quality, 83 had some degree of damage, with the
lowered semen quality being directly affected by the severity of
the scrotal lesions. Bulls with the worst cold weather damage had
the lowest semen quality and some were permanently sterile.
A more extensive
study was done (in 8 states and Alberta) in l965 following
blizzard conditions over much of the West during December of
1964--after a number of veterinarians noted serious frostbite in
many herds when examining bulls that spring before the breeding
season. Of the 6,389 bulls examined in that study, 14.4% had
scrotal frostbite, with significantly inferior semen quality. The
results of the survey were put together at Colorado State
University, and a report was published Sept. 1967 in the Journal
of the American Veterinary Medical Association.
Defects in sperm
were directly proportionate to severity of 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 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
adversely affected in many damaged bulls; some refused to service
cows for 6 months following the blizzard. Several bulls were
checked again later; those with most damage remained permanently
infertile, while others with less severe frostbite eventually
recovered. The bulls with questionable semen quality after an
initial evaluation generally have a better chance of recovery than
those with obviously unsatisfactory semen. Several veterinarians
in the 1965 study reported that testicle swelling was always
associated with unsatisfactory semen quality.
Dr. Glenn Coulter,
Livestock Sciences Section at Lethbridge Research Centre,
Lethbridge, Alberta, says “scrotal frostbite of bulls is a common
problem in cold winters. It usually occurs in bulls that don’t
have adequate dry bedding or protection from wind. 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.” He 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. Moderate to severe
frostbite affecting 10 to 30 percent of the scrotal surface will
need a minimum of two months and perhaps as long as 12 months for
recovery, to restore normal fertility, if no adhesions occur
between the testes and scrotum. If adhesions occur, the loss of
normal fertility may be irreversible,” he says.
A bull’s testicles
are very sensitive to temperature changes. Cold weather causes two
extremes in temperature in the scrotum. First there is
supercooling at the onset of frostbite. The second extreme is
superheating as the frozen tissue thaws and inflammation occurs.
Supercooling is temporary, while the superheating can last 10 days
after the initial injury. Inflammation causes swelling, and
testicle swelling always produces lowered semen quality.
Dr. Mickelson says
extent and reversibility of the damage to a bull is directly
related to extent of damage within the testes. Some bulls exposed
to extreme cold can suffer sperm damage even if they escape
scrotal frostbite. 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 1965. The weather conditions that caused problems that year
were rain turning to ice and snow, accompanied by several days of
temperatures lower than minus 10 degrees F. and winds gusting up
to 60 miles per hour. The wind chill factor was equivalent to
about 70 below zero F.
Problems also
appeared in many bulls following severe winters of 1978-79, 1984,
and 1989. Dr. Mickelson says many bulls suffered permanent
infertility following the February 1989 blizzard, but a high
percent of affected bulls recovered in time for the breeding
season. The February 1989 “Siberian Express” brought blizzard
conditions to much of the west, with wind chill factors equivalent
to minus 100 degrees F. Many cattle died during that storm.
Bulls can recover
from scrotal frostbite, he says, if there are not 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 in 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, stockmen should
check bulls for signs of damage. Blisters and scabs will be
obvious for about three weeks after the frostbite happens. Scabs
will fall off in about a month, leaving reddish-pink scar tissue.
If there is evidence of frostbite, check the extent of injury. 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, says Mickelson, 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.
Windbreaks and good
bedding during bad weather can help prevent testicle freezing.
Bulls being trucked in cold weather should be protected; traveling
in an open truck creates a serious wind chill factor. Good bedding
can provide insulation and protection; 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. Wait at least 40 days after the 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.
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