Detecting pregnancy in beef cattle

by Tamara Scully

According to 2016 USDA data, only 20 percent of beef herds are actively using rectal palpitation or ultrasound to detect pregnancy. While 70 percent of producers with herds of 200 head or more do use one of these methods, a mere 11 percent of those with 49 head or less do so to detect pregnancy. According to Dr. Ky Pohler, Texas A&M University, the beef industry is leaving a lot of income on the table because these accurate pregnancy detection methods are better utilized.

“We need to think about developing pregnancy diagnosis strategies in order to help us minimize this loss and maximize our profitability,” Dr. Pohler said in a recent webinar sponsored by the National Cattlemen’s Beef Association.

Beef cattle do not have any issues with fertilization rates, Dr. Pohler said. The fertilization rate for beef cattle bred based on standing estrous is 95 percent.

The earliest that pregnancy can be accurately detected in beef cattle is at 28 days. But beef cows often suffer undetected embryonic losss early in pregnancy, before 28 days post-conception. These cows simply end up getting bred back to the bull, as they cycle again, and most likely will conceive again. These early embryonic losses reduce the initial 95 percent conception rate to about a 70 percent pregnancy rate.

But calves conceived at this later time will be at least 21 days younger than those day zero calves who were conceived via the initial round of Timed Artificial Insemination (TAI) and carried to term. The difference in weaning weight between day zero calves and the calves from cows that first had early embryonic loss is about 50 pounds, Dr. Pohler said.

A later period of embryonic loss occurs after the detection of a heartbeat and prior to day 60. These late losses account for a loss of about eight percent, bringing the overall pregnancy rate down from 70 to 62 percent. These cows are bred back to the bull at the end of the breeding season, and their calves will be over 100 pounds lighter at weaning than the day zero calves.

“We’re losing money in both situations, however in the late embryonic loss, we leave a lot of money on the table there,” Dr. Pohler said.

If farmers aren’t using pregnancy diagnosis tools, and don’t know whether or not a cow is successfully carrying a fetus, they can’t make the best management decisions. Cows that never conceive are “an expensive cow,” Pohler said, and simply knowing that conception hasn’t occurred can lead to better management decisions such as changes in feeding protocols or culling of open cows. A herd’s reproductive efficiency can’t be evaluated if it isn’t known if cows did conceive, and when in the pregnancy any losses occurred.

Diagnosing pregnancy

Selecting a detection method that works best for each herd is the key. Facility limitations, labor, or animal handling and stress can be factors to take into consideration when selecting what works best on each operation. “There’s a lot of different technologies that are on the market and available for pregnancy verification and diagnosis,” Pohler said. “Pick something that works well for you.”

Waiting for the cow to calve is ultimately effective, but not efficient. Manual or visual examination of the abdomen for pregnancy can only be done after 180 days, too late to re-breed cows with early or late embryonic losses.

More useful diagnostics include manual rectal palpitation, which can accurately detect pregnancy after 35 days.

Ultrasound is accurate at 20-30 days, while blood tests can also detect pregnancy during this post-conception period.

Beginning at day 35, rectal palpitation allows changes in the uterus to be felt. These include the presence of fluid, membrane slip, or a detectable fetus. It is easier to accurately diagnosis pregnancy via palpitation as the fetus develops.

Ultrasound can detect the fetus at about 28 days, and is nearly 100 percent accurate. It also detects the heartbeat, and can identify the age and sex of the fetus.

Specialty doppler-based ultrasounds can detect pregnancy between day 18 and 20. Other 3D and 4D ultrasound technology is also available, but not commercially viable at this time.

Chemical tests, particularly the Pregnancy Associated Glycoproteins (PAG) test, have been found to be 90 to 99 percent accurate. A blood sample from the jugular vein – dairy producers can run the test on milk – is required. ELISA testing results in a positive or negative determination of pregnancy. The PAG test is considered accurate after about day 30 of pregnancy, when the cells responsible for producing the protein are formed.

Three companies offer the PAG laboratory test for on-farm use. Samples are sent back to the laboratory, with results available within one to three days. A complete on-farm “pseudo” PAG kit is on the market, and provides a visual display which indicates whether pregnancy has occurred or not.

Because PAG levels are at their baseline 60 days postpartum, cows can be artificially inseminated at day 65 and tested 30 days later. If PAG levels are increasing, then the cow is pregnant. PAG levels increase from day 24 after conception until the day of calving, when the decline slowly down to the baseline level.

Using PAG testing prior to day 24 is not as accurate, Pohler said. Many cows with elevated PAG levels between day 24 and 28 are no longer pregnant by day 30 when an ultrasound is performed, suffering an early embryonic loss. Increasing PAG levels during early gestation are indicative of successfully maintained pregnancies.

Pohler explained that future pregnancy diagnostic testing could be “based on this idea of trying to identify cows that are going to undergo embryonic fatality.”

Research correlating PAG levels to the loss of heartbeat on ultrasound show promise in doing just that. PAG levels in cows have been seen to decrease several days prior to seeing embryonic heartbeat loss on the ultrasound. And cows that successfully calve have been shown to have higher PAG levels at 30 days post-conception than those who ultimately go on to have embryonic loss.

PAG levels offer a “strong indication whether you’re going to have a successful pregnancy or not,” Pohler said.

Early embryonic losses, between day 17 and day 31, remain a challenge for beef cattle pregnancy diagnostics. As pregnancy can be detected earlier, using newer technology, higher rates of early embryonic loss will be noted than are currently able to be detected.

Rectal palpitation, ultrasound and PAG testing are all proven, reliable means for beef cattle producers to track reproductive efficiencies. Utilizing one of these methods makes economic sense.

“Use a proven method of pregnancy diagnosis… in order to maximize your success.”

2019-08-29T13:49:59-05:00August 29, 2019|Eastern Edition, Western Edition|0 Comments

Leave A Comment