Proper care and management of bulls
is crucial for optimum fertility. Some bulls are naturally more
fertile than others, due to genetics, scrotal conformation, etc.
but poor management can reduce a bull’s fertility or his chances
of siring a high number of calves. Bulls that are too fat or too
thin will not have optimum fertility and may have other issues
that impede their ability to breed cows. Young bulls need
adequate nutrition to develop properly, but should never be fat.
Nutrition
Ron Skinner, DVM, (veterinarian and seedstock producer near
Hall, Montana) says you need to monitor the condition of all
your bulls, just like you would your cows. “Inadequate nutrition
is detrimental to the fertility of both. Semen production of an
underfed young bull is only 77 percent of the production of an
adequately fed bull. If a bull has malnutrition and is in a
tough situation, his semen production will drop to that lower
figure very easily,” says Skinner. “If you don’t give him the
proper tools to work with, he cannot perform at his peak,” he
explains.“The interesting
thing about this is the fact that if a young bull is allowed to
get too thin, he will still lag behind in his semen production
for the rest of his life, even if his nutrition is brought back
up to speed. People often don’t realize this, but this was shown
in a study that was done many years ago by T. D. Rich at
Oklahoma State,” he says.
“Poor energy levels will delay
puberty. A young bull that is not developed properly
nutritionally will be slower maturing, so the purebred breeders
who are developing bulls need to have them on a proper energy
ration—not too much and not too little. If bulls are going out
to work as yearlings, they need to be developed at a proper
level. A 2.6 pound average daily gain is an ideal rate of gain.
There is some debate over this, however, because most young
bulls are being fed to gain 3 to 3.5 or even 4 pounds per day.
You want that bull to be bloomy, but you don’t want him to be
fat.” A young bull that is overly fat may have fertility
problems.
“He may also have less actual
testicle size. There is a tendency to increase testicle size
with fat deposition in the scrotum, but the lack of circulation,
due to the extra fat, has a tendency to decrease actual
testicular tissue (hence less size—less scrotal circumference--
after the fat is lost). Therefore you end up with less semen
production.”
Most people know that fat
decreases fertility, but bull breeders still want to have their
bulls look really good in the spring; ranchers still tend to
prefer the bulls that are big for their age and have shown how
much they can gain. People still get hung up on this, and it’s
hard to get by the old idea that fat is pretty. In practicality,
however, a daily gain of 2.6 pounds is optimum. “At the
University of Missouri, Robert Larson DVM, PhD did some good
research on this, following those bulls out for an extended
period of time, evaluating semen production and semen quality
later in life,” says Skinner.
“Excessive energy levels, getting
bulls too fat, will also decrease their libido, especially in
older bulls. If you overfeed them and they are too fat in the
spring they will be lazier because they just can’t move well
until they get some weight off,” he says. Bulls need to have
some reserves, however, especially a young bull that is out for
the first time breeding cows; he needs to have something to draw
on when he doesn’t have time to eat. You don’t want him fat, but
you want him in good condition.
“If we don’t take care of bulls
properly during their growing period or during their off season
when they are not with the cows (and they are short-changed on
nutrition), there is a greater chance of sub-optimal fertility.
Then we end up with less cows bred and settled in their first
cycle and a strung out calf crop. You’ll have a lower average
weaning weight due to a higher percentage of late calves. You
should have at least 85 percent of your calves from the cows’
first 2 cycles during breeding season, depending on the
condition and fertility of the cows, the type of breeding
pastures, etc.”
A good mineral program is an
important part of your nutrition management. You need a balanced
program with the appropriate levels of trace minerals to
complement your feeds. The bulls should be on the same mineral
program as your cows, to make up for any lack in your soils (and
pasture plants) or feeds.
Disease Protection
Bulls should be on a good health program, just like your cow
herd. “Several things play a role in cattle health and the
fertility of a bull—nutrition, genetics, disease, and stress
(the latter can hinder the immune system and make an animal more
vulnerable to disease, or cause recrudescence of latent
disease). Reproduction in a bull is no better than the weakest
link in that chain,” says Skinner. The bull may be infertile or
may have sub-optimal fertility.
A low pregnancy rate in the first
half of the breeding season—in the cows being bred by a certain
bull—may be the result of sub-optimal fertility due to any one
of those factors. “If you have a bull in a single sire group
that is not getting as many cows settled as he should, it could
be that he’s still fertile but not as fertile as he should be
(optimal fertility will be challenged), due to a weak link in
that chain,” he explains.
“Bulls need to be vaccinated
before breeding season. Often they are neglected or left behind
in all the cattle processing. It comes time to turn bulls out
and people realize they haven’t been vaccinated. Bulls should be
vaccinated well ahead of the breeding season,” says Skinner.
It’s not wise to vaccinate bulls the day you turn them out.
Depending on age of the bull and what you vaccinate for, the
time it takes for immunity to develop after vaccination can
vary. A booster shot does not take as long as a first time shot.
If the bull has stresses, or reactions from vaccination, this
may compromise his abilities for a while during the start of
breeding, depending on the vaccine.
“IBR vaccine, for instance,
should be given long enough ahead of time that the animal, if
stressed, can get past any recrudescence of the IBR virus and
any shedding of the virus.
This may take 2 weeks. If you
give the vaccine 30 days ahead of time the bull should no longer
be shedding virus by the time you turn him out,” says Skinner.
“Some people will tell you it’s better to vaccinate at least 60
days ahead, so that if the bull has a fever, he’ll have a new
batch of sperm cells by breeding time. But the bull will be
going through a stress period as soon as he goes out with the
cows, that first 30 days, and he needs some immunity. We find
that IBR recrudesces in a cow during the stress of estrus, and
if the bull is going into a herd that is not properly
vaccinated, he is apt to be challenged, from that cow herd.” You
want him to have peak immunity, to protect him, during that
first 30 days, as well as no temporary impairments from his own
vaccination that might hinder his fertility or ability to breed
cows at this crucial time, so vaccinate him several weeks ahead
of turnout. In many cases you’ll be vaccinating semi-annually
(fall and spring) depending on your area, and your
veterinarian’s advice. So plan ahead and have a good vaccination
program for the bulls, just as you would your cows.
Exercise
Bulls need exercise during their off season, so they will be fit
and athletic before they go out with the cows. “They are
athletes, and you will decrease the incidence of injuries if the
bulls are physically fit at turnout. Just like a football
player, a horse, or any other athlete, there will be less
injuries if bulls are fit,” says Skinner. Also, an athletic bull
can cover the territory, spend more time chasing and breeding
cows without tiring, than a soft, out-of-shape bull.
“If you lock bulls up in a small
pen with no exercise and feed them heavily, this is detrimental
to optimal breeding conditions. We leave our bulls on mountain
pasture, with a mineral supplement and a minimal amount of
alfalfa hay,” says Skinner. “Bulls need to be in a large area,
where they can self exercise during winter and spring, but you
still need to manage and take care of them, and not just forget
them.”
Cottonseed Caution
Whole cottonseed is a feed that should be avoided for bulls,
especially young bulls. “The glossypol in cottonseed can cause
trouble. If you feed any cottonseed-type supplement, such as for
a protein source, make sure it doesn’t contain any glossypol,
because it can certainly be damaging to testicles,” he says.
Cottonseed is a nice energy/protein supplement but it can be
detrimental to bulls.
Glossypol, fed to young growing
bulls (6 to 12 months of age) results in decreased sperm
production and an increase in sperm abnormalities. “If there’s a
low level of glossypol it will adversely affect the mid-piece of
the tail (of the sperm cell) and if there’s a high level it will
make the bull completely infertile,” explains Skinner. It can
also adversely affect sexual behavior in bulls.
A recent study showed that to
avoid problems, the use of whole cottonseed should be limited to
10 percent or less of the total diet for young bulls, even
though it may be an acceptable feed for mature bulls during part
of the year. One recommendation is that bulls should be taken
off whole cottonseed for at least 90 days prior to the start of
the breeding season, to ensure that there will be new sperm
present—that were not negatively affected by glossypol. Do not
supplement the cow herd with whole cottonseed during the
breeding season or bulls may be exposed to its negative effects
on sperm.
Other Factors That Affect Fertility
Age can make a difference; a bull’s highest fertility is at 2 to
4 years of age, on average. “After 4 years there may be some
decline in fertility, but this is not very noticeable until a
bull gets to be 5 or 6 years of age. At 7 years, on average, you
start to see a more rapid decline.
This will depend on the
individual bull. There are some bulls that will have good
fertility at that age and others that will fall apart on you by
then, according to trials that were done in Oklahoma by T.D.
Rich,” says Skinner. “The 5 and 6 year old bulls may not have
declined significantly from their peak fertility at age 4, but
it will depend on their genetics.”
Overuse can also decrease
fertility, though this decline is usually temporary. “A bull may
have poor fertility because he is exhausting his semen supply,
especially if he is not producing semen as well as he should,”
says Skinner. Overuse can be a bigger problem in a sub-fertile
bull than a highly fertile bull.
“If a bull is being used very
heavily, usually a 7 day rest will bring him back to full speed
on semen count and semen production. Rotating bulls in and out
of the cow herd during the peak of breeding season (in for a
week, out for a week) is not a bad strategy, but if a bull is
healthy, heavy use is not damaging to his reproductive
abilities, unless he becomes injured,” says Skinner. He may
deplete his semen supply under heavy use, but should be able to
come right back after a short rest, even just an overnight rest
if he only bred a few cows that day, since there are always more
sperm developing. If a bull is trying to breed numerous cows day
after day and is dragged down nutritionally, however, this is a
bull that needs to be taken out for a week and not just
overnight.
Weather is also a factor. Pay
attention to bulls in cold weather, especially if there’s wind.
Wind chill that lowers the effective temperature can lead to
scrotal frostbite, especially in older bulls with large
testicles, if they are unable to draw them up close enough to
the body for protection against the cold. If weather is severe,
bulls need good windbreaks, and bedding, to protect their
testicles from frostbite.
Hot weather can be detrimental
also. “In 100 degree weather, a bull loses some breeding
capability and fertility, and this is something we have no
control over. Heat is detrimental to sperm production,” says
Skinner.
High fever will also make a bull
infertile for a while. “His semen may be ok for a few days after
the fever (because the sperm that were already mature will be
fine), but he will be in trouble later. It takes 60 to 63 days
for sperm cells to develop,” says Skinner. Closely monitor your
bulls year round. If a bull gets sick and ends up with a fever,
you should definitely have him checked before he breeds
cows—especially if you are using single-sire breeding groups.
You need to be watching your bulls during the last 2 months of
their off season before you put them out with cows, to know they
are fully functional.
Semen evaluation should probably
be done on all bulls before turnout, unless you will have
several bulls out there. Everyone tries to figure out ways to
cut expenses, but the expense of a breeding soundness exam
usually pays off. One problem you can get into if you don’t
check your bulls—even if you have 4 bulls out with 100 cows—if
the dominant bull is infertile or sub-fertile, this may
negatively affect your calf crop even though the other bulls are
fertile.
“The dominant bull usually sires
60-plus percent of the calves. If he’s infertile, he may keep
the other bulls from breeding, even though he’s not settling the
cows himself,” explains Skinner. So having even one bad bull in
a multiple sire group can be a significant problem.
“Some of the bulls with
sub-optimal fertility may not be detected with a typical semen
test and breeding soundness exam, however. A bull may have
plenty of semen on that day, since he hasn’t been breeding
cows,” says Skinner. As soon as he goes out to breed cows,
however, he tends to run out of sperm because his production may
be poor. If you keep him out of the cows for 48 hours, he may be
ok again, but this kind of bull won’t settle as many cows as a
more fertile individual.
“Libido is also something that
can’t be evaluated during that exam. You have to watch the bulls
after they are out with the cows. This is especially important
in single sire breeding groups. You have to make sure that young
bulls figure it out,” he says. Some work done at Miles City,
Montana showed that crossbred bulls reached sexual maturity more
quickly than purebred bulls and seem to have more libido.
Feet and soundness are also
important issues. A bull may be fertile, but if he can’t get
around or is in pain or uncomfortable from feet/leg issues or
becomes unsound, he won’t breed very many cows. Always check
feet and legs before bull turnout.
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