Cow Fertility
By Heather Smith-Thomas
Fertility is the most important thing in a cow herd. All the traits we select for are negated if the
cow doesn’t get pregnant or fails to carry a pregnancy to term. There are numerous reasons that a cow
might fail reproductively, and it is crucial to determine the cause of failure. When a cow comes up open
after the breeding season, or doesn’t have a calf after being diagnosed pregnant, it is important to find out
why—especially if it is not an isolated circumstance. Disease, nutrition, management, etc. can affect
pregnancy and calving rates in a herd and generally these problems can be corrected if we know what they
are.
Duane Mickelsen, DVM, a cattle breeder at Pullman, Washington (now retired from Washington
State University) has spent his lifetime specializing in reproductive problems in cattle—in private practice
or as a professor teaching bovine theriogenology and obstetrics to veterinary students. He has consulted in
a number of bovine herd infertility causes in Washington, Idaho, Oregon and Montana, and was the first
veterinarian to diagnose bovine trichomoniasis in Washington, Oregon and Montana in 1978. He still
works with a few herds, semen testing bulls and pregnancy testing cows.
Over the years Mickelsen has given cattlemen advice regarding whether to cull open heifers or
cows, or late calvers. He feels strongly that pregnancy checking is not just to determine whether a cow is
pregnant, but to also determine why not—if she’s not.
All too often herd owners hesitate to cull a favorite cow, and perpetuate a problem. “I ask if they
want me to bob that tail or mark her with paint to say she’s open and should go in the cull bunch, and the
rancher hesitates and says he’ll decide later. Then we get that same cow back the next year and she’s open
again!” says Mickelsen.
“I used to recommend that every open female be culled, just because too many people tend to keep
some cows that they should be selling,” he says. There are certain instances, however, in which the
decision to keep or cull should hinge on other factors, especially in first calvers that come up open after
raising their first calf.
A STUDY OF 8000 COWS - “One year my students and I checked more than 8000 beef cows and kept
careful records. We found the open cows and palpated them a little more extensively to see if there was a
corpus luteum on the ovary, which would indicate cycling. If the ovaries were small and static with no
activity, or the uterus felt inactive or unhealthy (perhaps atrophied and thin-walled) we made a note of
those cows. We also noted the ones that had pyometra or a mummified fetus,” says Mickelsen.
“We’d find a lot of those mummified fetuses in the pelvic cavity. Those cows were probably
aborting but the fetus had not completely gone out—and we’d find it lying up there with the cervix closed.
The fetus just sits there and dries out. Those cows definitely need to be culled,” he says.
“We saw quite a few open cows with an involuted uterus, which signified abortion. Some cows
really make you look bad in your preg checking. You call them pregnant and then a few days to a few
months later they slough the fetus. A few ranchers started calling me to say that quite a few of the cows I’d
called pregnant didn’t calve. That’s when I started looking a little closer and discovered trichomoniasis.
Those cows were pregnant early on, but lost the fetus,” he explains.
“When we examined the 8000-plus cows that year, we classified them all into age groups. There
were more than 1000 heifers (yearlings exposed to a bull, that should be pregnant with their first calf), and
a high percentage of them were not pregnant. The next group were 2-year-olds that had a calf and should
have bred back again for a 2nd calf. A similar number of them did not get pregnant,” he says.
“One reason for poor breed-back on this age group is dystocia (difficulty calving). In an earlier
study researchers found that about 16% of heifers don’t breed back because they haven’t recovered quickly
enough from calving. Calving ease is a major factor in a heifer’s future ability to breed back. It’s
important to select a bull that sires small calves. I personally feel that Wagyu bulls are a good choice for
breeding heifers because they sire smaller calves an easy-calving bull of other breeds,” Mickelsen says.
His study found 25% open in the coming 3-year-old group that should have been pregnant with a
second calf. “A good percent of those could be due to dystocia, and another factor in this group can be
inadequate feeding, especially during the last trimester of gestation when they were heifers are carrying
their first calf.” A heifer pregnant with her first calf is still growing, and if she doesn’t have adequate
nutrition for her own growth and for her fetus, and for lactation, she won’t cycle soon enough to breed
back.
“A lot of cattlemen still believe that if they feed heifers too well during the last trimester they will
have bigger calves and more calving problems, so they don’t feed their heifers adequately.” They are
shortchanging the group that needs it the most.
“Inadequate feed will reduce birthweight a little, but is detrimental to the heifer, and to her ability
to create adequate colostrum, so this is why you need a guaranteed calving-ease bull and not shortchange
those heifers. If you feed them poorly during their last trimester it causes too many problems. The heifer
puts it all into the calf and won’t breed back,” he says.
“The most successful group of all, in our study, were the 6000 cows in the 4 to 9- year-old age
group. They are in their prime and tend to have good body condition. They have matured (no longer
needing extra nutrients for growth) and know how to get to the feed trough the quickest. In that group
about 97% were pregnant,” says Mickelsen.
“The last group included old gummer cows that were starting to lose weight. Only 78% of them
were pregnant,” he says. This might vary from ranch to ranch, depending on the feed program,
management, health program, and genetics of the cow. Some, especially crossbred cows, tend to last
longer in the herd before they seem “old”.
“I had some clients who took really good care of their cows. They lived with them, always
monitoring them and knowing how they were doing. These ranchers worked hard at it and didn’t have very
many open cows. I enjoyed working with them. The better clients were always willing to listen to me and
I always listened to them because they had a lot of knowledge. I told my students that the day they quit
learning is the day they should quit. There is always something more to learn,” he says.
Some of the larger herds were harder to manage, especially the ones on big range pastures where
it’s harder to keep track of all the cows or make sure they had adequate pasture, a good vaccination
program, etc. “A good vibrio vaccination program, along with giving the cows lepto 5, seemed to help a
lot. We didn’t see much IBR/BVD in those herds. Our main problems seemed to be trichomoniasis and
nutritional problems (inadequate energy in the diet),” explains Mickelsen.
“In herds where 25% of the replacement heifers came up not pregnant, I’d ask two questions.
Number one was what’s the fertility of the bull(s). Number two was nutrition, and this was usually an
energy problem, where the heifers were not cycling.” They hadn’t grown adequately to reach puberty on
time and weren’t fertile yet.
“Inadequate nutrition can delay puberty, lower conception rates, decrease skeletal and muscle
growth and increase the frequency of dystocia and failure to cycle again after calving. One study showed
that with poor nutrition the follicle just degenerated and the animal failed to come into heat,” he says.
Pregnancy is a luxury; the female must be healthy and in good condition in order to become pregnant.
“In one group we looked at, 87% of the heifers were not cycling, due to lack of protein and energy
in their diet. Sometimes it’s partly genetics if the heifers are big-framed slow-maturing cattle, especially if
they haven’t had adequate feed. Our study brought out the fact that in this group it was primarily a feed
problem. A lot of ranchers just turned their heifers out on grass in the spring, which is fine as long as the
grass is adequate. If it’s a late spring sometimes the grass is marginal,” says Mickelsen.
“Most of the time we assume the heifers are with virgin bulls. If they are not, you could have a
disease problem like trich or vibrio,” he says.
“I am always more inclined to cull any heifer that did not get pregnant the first time than I would
the first-calf group (the young cows that were trying to lactate and raise a calf, grow, and start cycling
again). That young cow has already proven herself, and the rancher simply may not have fed her
adequately to rebreed on time. As long as the reproductive tract is normal, I generally recommend keeping
this open young cow, especially in light of the fact that it costs a great deal to replace her (whether you buy
or raise the replacement).” If she milked well and raised a good calf, and you just didn’t feed her enough to
start cycling again, you could gamble on her and keep her. If she has a puny calf and didn’t take good care
of it and still comes open, however, she is a cull.
The 4 to 9-year-old cows had the best pregnancy rates, and then the older cows (10-plus years of
age) were having problems with nutrition as their teeth became worn out or lost. Studies have shown that
cows use their bottom incisors along with their tongue to tear off grass. “If they have marginal popcorn
teeth or have lost teeth, they just can’t keep up with the other cows, nutritionally.” If they are being fed
hay, they can pull it into their mouth with their tongue, but it’s hard for them to tear off grass as they graze.
“When I preg-check in the fall I also check the teeth on older cows. I don’t know how many times
I got bruised ribs trying to hold a cow’s head to check her teeth! Some ranchers had chutes that hold the
cow’s head out, but most of the time I was trying to check the teeth while a cow was slinging her head
around. We had several ways to determine the cow’s age besides checking her teeth. Sometimes the ear
tag had the year she was born, or a Bang’s tag or tattoo in the ear (but you have to get to the head to look at
it), and some ranchers would fire brand the year number on the shoulder. We made note of the age of every
cow in our study. It’s good to know the age of each cow in the herd, just for culling purposes,” he says.
“When teeth become worn down, I tell clients to get rid of those cows. If they are not fed well,
those old gummer cows generally have problems when they calve again. They may calve, but some don’t
make it through the calving or don’t milk enough for that final calf and it’s a runt.” Those cows end up thin
and may be just skin and bones by the time you do sell them. It’s better to cull them before they reach that
point.
“Group number one (replacement heifers that have been with a bull) and group number four (the
older cows) are the ones to cull most diligently. With the price of cattle today it’s easier to get rid of the
open ones, but in the past a lot of ranchers were tempted to keep the open cows, or the older thin cows
another year and get another calf out of them or keep a heifer that wasn’t pregnant, in hopes she would
breed the next year. A lot ranchers paid for that decision in perpetuating problems,” he says.
“When I’m checking a herd, I make sure the ones that seem pregnant are indeed pregnant, and
check the non-pregnant ones farther and write down whether they are cycling or non-cycling. If they are
cycling but not pregnant, this means there must be an infection or a bull problem. If they are non-cycling
we are usually looking at a nutrition problem—usually energy or maybe inadequate protein.”
“I really enjoy fertility work because it really helps the rancher. It should go beyond whether the
cow is pregnant or not, because we need to determine why this cow is not pregnant.” This is an important
part of the task because it may lead to discovery of a herd problem that needs to be addressed.
“We could go for years and not help that client at all if we just determine which cows are pregnant
and which ones should be culled because they are not pregnant. We need to know why cows are not
pregnant,” he says.
“If I can’t feel a pyometra (enlargement in the uterus due to infection), I start looking for
something besides trich. I may pull blood samples and see what the titers are, but in most cases it boils
down to trich or possibly vibrio if they haven’t been vaccinated adequately. A good practitioner in
southern Idaho that I worked with, Dr. Craig Rowan, always told me that if a rancher uses a good vibrio
vaccine annually on the cows, this would increase pregnancy rate about 5% and I think he was correct,”
says Mickelsen.
Cattle that have fenceline contact with other herds (and bulls going through fences) or graze in
community pastures on public range, are vulnerable to problems. It always pays in these situations to
vaccinate for vibrio. Occasionally small breeders will purchase, lease or borrow a used bull, and this can
be a recipe for disaster.
TRICHOMONIASIS - This venereal disease can sneak into a herd and cause significant loss of
production due to higher rates of open cows and late calvers. “When I first started teaching here at WSU
there was a big need for palpating/pregnancy testing herds in this area, so I was helping with that and
teaching my students. During my 30-some years of doing beef herd health—which was mainly in the fall,
preg-checking cows—I had between 2500 and 9000 cows per year that I took students out to teach how to
palpate cows. Then I diagnosed trichomoniasis in several of those herds, and another herd in Montana and
one in Oregon, just by palpating cows,” says Mickelsen.
“It can be difficult sometimes to determine the difference between a pregnancy and the
enlargement (fluid-filled sac) in the uterus caused by pyometra from a trich infection. A lot of
veterinarians over the years have felt that blob and thought it was a pregnancy. I may have done it, too, in
some cases, until I began to look at this more carefully,” he says.
“When I find a cow that does not have the 4 positive signs of pregnancy (and just has an
enlargement in the uterus) I always check farther. The positive signs include amniotic vesicles, cotyledons,
a fetus, and being able to feel/slip the fetal membrane. The latter is one of the earliest clues and by my later
years of palpating I could detect a pregnancy as early as 28 days. But a cow with trich simply has a fluidfilled, thin-walled sac that feels like a pregnancy,” explains Mickelsen.
“I’d feel that sac and then go up and down that whole horn and not be able to get a fetal membrane
slip. So this would be cause for suspicion and I’d insert a pipette into the uterus and get a potato soup kind
of fluid with a distinctive smell. Pus has a foul odor, but this fluid smells sweet and is unmistakable. So I
would look at the fluid under a microscope and see all these little trich organisms swimming around,” he
says.
“I diagnosed this in several herds. In one herd of 1500 cows, 400 were open. Some were
discharging pus and some were not. We tested all the bulls and found which ones were negative and which
ones were positive for trich. We tested those open cows and found out which ones had trich. I was going
to do a study to see if ivermectin would work to treat them (since it kills the organism), but couldn’t get to
them again for about 4 months. So I decided to set up a different trial, and the rancher was willing to let me
see if those cows would breed back,” says Mickelsen.
“We took 20 of his virgin 2-year-old Charolais bulls and put them in with the 400 open cows—
some of which were discharging pus. Three months after we put the bulls in, I preg-checked them and 92%
of them were pregnant; they had overcome the infection and were able to breed back. Then we tested the
20 bulls, and 12 of them showed positive for trich. They had picked it up from the cows.” In a herd where
trichomoniasis has come in, bulls would continue to be infected by some of the cows they bred, and would
keep it going in the herd even though infected cows eventually recover from the infection.
“This is why today the state regulations require a herd quarantine when trich is found, and the
owner has to sell the open cows. The problem in the past is that people didn’t recognize it for what it was,”
he says. Some people would cull their open cows, but other ranchers might buy them at the auction and
bring them home. It was a vicious cycle that spread this disease to other herds. Now many states require
testing of bulls.
“When I went to Montana and diagnosed trich in 1978, the veterinarians there thought it was a
lepto problem. I had one of my students from Dillon, Montana, Dr. Tom Williams, submit samples to the
Montana state diagnostic lab. When the lab got it they said it was negative. I sent another sample from
Pullman after I got back, and told the lab to look at it before they put it in their medium to culture it,” says
Mickelsen.
“I also asked where they got their medium and they said it came from Ames, Iowa and was called
trich media. I was using a different medium and the trich organisms were growing in mine. I told them to
check the new sample that had already tested positive when I sent it. This time they said it was positive, so
I told them to put it in their medium and look it. They did, and the medium killed it immediately. So there
might have been a number of years that this disease was not being diagnosed—with vets submitting
samples and not getting a correct diagnosis. The state labs today have it figured out,” he says.