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Accuracy matters in cattle herd pregnancy checksAccuracy matters in cattle herd pregnancy checks

George Perry and his team at Texas A&M are using PAG testing to detect pregnancy earlier than ever in herds across the country.

Betty Haynes

June 21, 2023

4 Min Read
Beef cattle herd grazing on pasture
COW: “Figuring out of when the herd became pregnant is dollars to you, and as we back things up earlier, you can make more informed management decisions,” says George Perry, professor at the Texas A&M AgriLife and Extension Research Center. Betty Haynes

New findings have emerged in the animal science community to improve cattle producers’ bottom line by making timely management decisions.

“When we put things in different scenarios, the lack of knowledge costs money,” says George Perry, professor in beef cattle reproductive physiology at the Texas A&M AgriLife and Extension Research Center. “And in some specific situations, it delays your management decisions.”

Perry says delays in management decisions cost money through pasture use, culling decisions, rebreeding and AI pregnancy opportunities.

“Animals born or bred earlier will calve earlier and stay in the herd longer,” he explains. “If we know the animals that breed and conceive early, we can focus on them as they continue to multiply in the herd. Steers born early have heavier weaning weights, heavier final weights, heavier high carcass weights and better marbling scores.”

Only 78% of large herds and 30% of small herds use reproductive technologies in the U.S. Pregnancy detection is an effective management tool, but only if it’s accurate.

“If you have open cows in your herd, they’re costing you a lot of money,” Perry says. “Every missed estrus basically costs you three weeks of weaning weight — so, about 40 to 50 pounds per calf.”

Common pregnancy detection methods include:

  • turning out a cleanup bull

  • manual palpation

  • ultrasound

Each method has negatives, ranging from accuracy and training to cost of equipment. Instead, PAG assays, or pregnancy associated glycoproteins, have become more available for pregnancy testing.

“The only way to detect PAGs in a maternal blood supply is that if a placenta was there at some point,” Perry says. “PAGs can very accurately be used as a pregnancy test because the only way they can get into the circulation is if these cells have migrated from a fetus to the maternal side.”

Eight years ago, Perry wanted to find out if this technology could identify which cows were AI bred vs. natural service. His team ran a PAG rapid visual test from a blood test taken when cows were ultrasound-checked and found both methods were effective.

“With a single handling, we could actually pick out AI versus bull bred without all the labor of going through an ultrasound and the risk of abortions or anything else at 28 days,” Perry says.

As technology has advanced, new methods have come to the market using PAG tests. One is the lateral flow or Idexx Alertys OnFarm pregnancy test.

Perry and his team have compared blood samples from over 2,700 different animals and have found the lateral flow and rapid visual test to be just as effective as ultrasounds.

“All of these technologies are accurate,” he says. “We get good results with them, and it provides knowledge back to you.”

Perry says that compared to other PAG tests, the lateral flow test is shorter and doesn’t require specialized training or equipment.

Help with resynchronization

Next, Perry and his team wanted to apply the technology to see if they could use a PAG test to resynchronize animals.

“We know with most fixed-time AI protocols, you get 50% to 60% pregnancy rates,” Perry explains. “What goes on with the other 40% to 50% that remain open?”

Perry ran PAG tests and performed a second synchronization 28 days after animals were bred, giving the animal two rounds of fixed-time AI in 31 days.

“We can implement these technologies pretty much chute side and benefit from them to resynchronize,” he says.

The findings concluded that an additional 15% of the herd was bred during resynchronization.

However, there are limitations to PAG testing. PAGs have long half-lives, causing concern for false positives, particularly postpartum.

“The recommendation by the beef reproductive task force is to wait about 45 days postpartum to start a synchronization protocol,” says Perry. “On your late-calving cows, that’s where you need to think about these false positives.”

Perry and his team are continuing to study modifications to detect pregnancy earlier through two rounds of fixed-time AI in a month.

“As we look at these things, it’s going to continue to improve,” Perry says. “I think we’re going to come up with more ways to implement this on your operations.”

Perry says if his team can detect pregnancy earlier, then it will be up to companies to get products to the producer level.

“What I want you to think about is how implementing technologies for pregnancy determination impacts your herd,” Perry says. “Figuring out of when the herd became pregnant is dollars to you, and as we back things up earlier, you can make more informed management decisions.”

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About the Author(s)

Betty Haynes

Betty Haynes is the associate editor of Prairie Farmer. She grew up on a Menard County, Ill., farm and graduated from the University of Missouri. Most recently, Betty worked for the Illinois Beef Association, entirely managing and editing its publication.

She and her husband, Dan, raise corn, soybeans and cattle with her family near Petersburg, Ill., and are parents to Clare.

Betty recently won the Emerging Photographer Award from the Ag Communicators Network during the 2022 Ag Media Summit and placed in the Emerging Writer category as well.

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