by Sally Colby
Pregnancy checking is an important aspect of gauging reproductive efficiency in beef herds, and helps producers monitor and improve reproductive efficiency.
“How many calves are weaned per cows exposed to the bull?” said Dr. Jessica Gordon, DVM. “If you’re pregnancy checking, you get a lot of information. If you don’t reach your target for number of calves weaned, it’s hard to determine where that’s coming from. Is it because they aren’t being bred, or are getting bred but not pregnant, or are they aborting?”
Pregnancy checking can lower herd feed costs because potential culls found to be open can be marketed immediately. Through pregnancy checking, the veterinarian and herd owner or manager can identify and address disease and nutritional issues.
Rectal palpation, which involves direct palpation of the fetus, is the most widely used method for pregnancy detection. “Depending on where the cow is in her pregnancy, we can palpate parts of the calf, whether that’s head or feet, starting at about three months’ gestation,” said Gordon. “Or we can palpate the cotyledons, the connection between the uterus and the fetal membranes. Those are palpable at about three months’ gestation.” Prior to two months, rectal palpation can reveal an amniotic vesicle, or the veterinarian can grab the side of the uterus and check for membrane slip – both indicators of a pregnant cow.
The cost of palpation varies among veterinary practices. Although it doesn’t require special equipment, considerable skill is needed to reach efficiency and recognizing the positive signs of pregnancy. Although accuracy varies by practitioner and age of the fetus, experienced practitioners achieve up to 99 percent accuracy. Palpations conducted later in gestation are more accurate, and practitioners who have palpated more animals have a higher rate of success. Gordon said the earliest detection of pregnancy by rectal palpation is at about 35 days.
One advantage of rectal palpation is immediate results. “The practitioner is there, tells you pregnant or open, and can tell you about how long into gestation that animal is,” said Gordon. “That can help if you choose to manage groups of cows differently.”
However, rectal palpation cannot determine the sex of a calf and affords limited ability to determine fetus viability. “As a fetus is becoming ready to abort, you can feel the changes in the fetus or the amniotic vesicle,” said Gordon. “It becomes a bit more ‘squishy,’ and practitioners who are used to palpating animals can tell that relatively easily.” Since palpation cannot detect heart rate, it’s possible that palpation is taking place before the breakdown of the fetus has begun.
Another method for detecting pregnancy is rectal ultrasound. Success with this method varies depending on how many days the animal is pregnant. It’s up to a skilled veterinarian to determine what’s what on the ultrasound screen because at 35 days, it won’t look much like a calf. “With rectal ultrasound, you can get a picture of the heart and see the valves moving,” said Gordon. “We can make sure the heart rate is good and the heart is functioning properly. That helps us determine the viability of the fetus.”
As gestation progresses, it becomes easier to identify a calf in utero with rectal ultrasound. Skilled practitioners can also sex calves at a certain point in pregnancy. “Later in gestation, we’re looking for the cotyledons because it’s challenging to get the calf into a position where you can look at it for an ultrasound,” said Gordon, “so we look for white masses, which are the cotyledons.” Experienced practitioners can often determine the sex of the calf.
The cost of rectal ultrasound varies among practices but it’s usually higher than palpation. The method requires special equipment, including an ultrasound unit and the hands-free probe for reaching into the rectum. It requires skill to manipulate the uterus to obtain an image on the ultrasound screen for accurate reading. Rectal ultrasound is faster than rectal palpation, which is an advantage in large herds. Although accuracy varies, it can be as high as 99 percent. Gordon said because rectal ultrasound saves wear and tear on the practitioner’s arms, some vets will offer the service at the same price as rectal palpation. The earliest detection of pregnancy with rectal ultrasound is at about 28 days’ gestation.
Some beef herd owners use a blood test for pregnancy detection. Gordon explained that the test checks for a specific B protein associated with pregnancy. “The skill for collecting blood from an animal is much easier to learn than palpation or ultrasound,” she said. “When you’re collecting a blood sample, you can see exactly what you’re doing and it’s a fairly easy skill to master. A lot of producers can master the skill on their own and can collect blood without the assistance of a veterinarian or technician.”
The cost of blood testing for pregnancy is similar to that of palpation or ultrasound. Most sources of the blood test offer kits that include the appropriate needles and blood collection tubes, and a means by which the test can be shipped to the lab for testing. Blood testing for pregnancy is easy to learn, is less invasive and is cost-effective for small herds and herds that lack easy access to a veterinarian. The earliest this test is effective is at 28 days.
However, the blood test only gives a positive or negative result – it doesn’t provide any information about calf viability or the age or sex of the calf. Because the test is sent to a lab for results, producers can’t make decisions at the chute regarding open cows and can’t determine whether a problem is a bull issue, infection or nutrition. There’s potential for false positives in the case of pregnancy loss or calving within two months prior to the test.
Blood test accuracy is about 99 percent for open cows and about 93 percent for pregnant cows. “If the test says the cow is open, it’s going to be correct 99 percent of the time,” said Gordon. “If the test says the cow is pregnant, it’s going to be right 93 percent of the time – which means 7 percent of the time, it’s wrong.”
Gordon explained the reason for false values for pregnant cows. “It’s because the pregnancy protein we’re looking for in this test sticks around after fetal loss and after a previous calving,” she said. “If you’re testing an animal within the first three months after a previous calving, there’s a chance there will still be pregnancy-specific B protein from the previous pregnancy. If an animal just aborted or reabsorbed a fetus, the protein will still be present in the blood.”
Beef producers should realize that some degree of fetal loss is normal. “Loss of pregnancy between 30 and 60 days’ gestation is about 15 percent,” said Gordon. “Normally we aren’t checking most of these cows prior to 60 days, but if you are, expect about 15 percent loss during that period. Between 60 days’ gestation and calving, pregnancy loss is between 2 and 4 percent, which is normal biological variation. Most issues are genetic incompatibilities or something specifically wrong with the fetus.”