Late-Term Pregnancy Losses: Avoiding Risk Factors
Getting a live calf on the ground in the spring out of each cow confirmed bred in the fall is every cattleman’s goal. The loss of that calf before it is viable is devastating, both economically and emotionally. Causes can include physiological problems (such as hormonal imbalances), metabolic problems, toxicoses, genetic abnormalities and/or infectious diseases caused by protozoa, fungi, bacteria or viruses, according to Brett Webb, North Dakota State University Veterinary Diagnostic Laboratory.
“Abortions and stillbirths can be the result of a direct effect, such as viral, bacteria or protozoal organisms gaining entrance to the fetus,” said Dr. Gerald Stokka, NDSU Extension Veterinarian and Livestock Stewardship Specialist. “The fetus may have congenital defects that result in abnormalities noted at delivery or inherited genetic defects. Indirectly, abortions and stillbirths can be a result of an interruption of the connection between the fetus and the dam, or illness of the dam. The fetus is nourished and oxygenated via the placenta. This is a very intimate connection between the two, and any disruption can impact the fetus negatively or result in its death. Inflammation of this organ is called ‘placentitis.’ Bacterial, fungal and protozoal infections can cause placentitis. Mycotic abortions are one of the more common results of fungal infections.”
Reasons for late term pregnancy losses in beef cattle are often difficult to pinpoint. South Dakota State University Veterinary Diagnostics Laboratory statistics indicate that fifty-four percent of cases submitted between 2006-2021 had no specific diagnosis.
There is still much to be learned about the causes behind late term abortions in cattle according to Dr. Russ Daly, SDSU Extension Veterinarian.
“For more than half of the abortion cases we examine, no cause is found,” he said. “When a cause is found, it is uncommon for a specific germ to be implicated. In many cases, a non-specific inflammation in the placenta is noted but a specific cause of the inflammation isn’t able to be identified. There is a lot yet to learn about specific causes. If germs are found, they’re usually ‘normal’ kinds of molds and bacteria that cattle regularly come in contact with. In late gestation, a cow’s immune system naturally ‘ramps down.’ This means that bacteria and molds that are normally of no consequence to the cow can now be potential problems.”
With 2021 drought conditions limiting normal hay production, producers should be careful when feeding up old hay or feeding grain hay. Feed sources that might contain molds or nitrates should be used with caution during the last trimester of pregnancy.
“Avoiding feeding cows hay that’s visibly moldy is a good idea when the cows are in late gestation – although mold spores can be present in hay that looks pretty good too,” Dr. Daly said. “Feeding cows off the ground when they’re in late gestation is easier said than done for some operations but will limit the cow’s exposure to environmental bacteria that might be hanging around in the soil. In addition to molds, nitrates can be a cause of abortions in cows. If a particular feed source is a suspect, or if several animals abort in a short period after a feed change, it would be worthwhile to check nitrate levels in the forage. Higher exposures to nitrates can cause more severe problems in the cows.”
Dr. Janna Block, North Dakota State University Extension Livestock Specialist also weighed in on the subject.
“The number of late gestation losses due to moldy feeds would be extremely difficult to pin down. Most of the “data” comes from observations, and not controlled research trials. In addition, there are a lot of challenges with obtaining representative feed samples and in interpreting results of analyses. The best advice we can give is to avoid feeding moldy feeds to beef cattle due to the potential risks.”
Thanks to consistent vaccine protocols, viruses such as Infectious Bovine Rhinotracheitis (IBR) or Bovine Viral Diarrhea (BVD) only account for 2% of late term abortions diagnosed at SDSU.
“Producers should have their cows and bulls on a good reproductive vaccine program with input from their veterinarian,” Dr. Daly said. “This will help protect against those unexpected exposures to the infectious causes of abortions (BVD virus, IBR virus, lepto and vibrio). Even though we don’t diagnose these causes very often in the abortion cases that come to the lab, an exposure could be devastating to a herd.”
An area producer who asked to remain anonymous shared his experience with the ravages of BVD.
“We had three or four cows abort in February,” he recalled. “We lost another six during calving that were either stillborn or they were born around 55-60 pounds and weak; they would just lay there and not suck, and then a couple of hours later they were dead.”
A post mortem revealed the culprit: Bovine Viral Diarrhea. It was a devastating year; besides the calves lost in the spring, another half a dozen were persistently sickly and passed away during the summer and fall.
“We had always vaccinated our cows for BVD,” the producer said, “But we brought in about fifty outside cows. These cows had never been vaccinated. I think what caused the outbreak was giving a modified live vaccine to the calves while the cows were pregnant. We had some losses in our main herd but the percentages were much higher in the outside cattle. We probably lost ten calves out of those fifty head.”
Since then he has stuck to the killed virus BVD vaccine, vaccinating all the cows every fall.
“We give everything a shot when we preg-test and sell all our opens or anything that loses a calf,” he said. “We’ve been doing much better, with no further issues for nearly ten years. If you’re bringing cows in, make sure you know what vaccines they have had.”
Cattle producers who find signs that multiple cows in their herd have aborted should consider seeking a diagnosis.
“I usually tell producers that one or two abortions are within normal limits in most operations,” Dr. Daly said. “After the second or third one, I feel that now it’s time to consider lab testing – primarily to rule out infectious or toxic problems that could be affecting the whole herd. In addition to the whole fetus, it’s valuable for the lab to receive placenta from the case as well. Many times germs or abnormalities are found in the placenta but not in the fetus itself.”
“I am not a veterinarian, but I would say that if abortion rates exceed 1-2 percent of cows in the herd, it is past time to take action!” Dr. Block said. “Most of the time, after one or two cows have slipped their calves, producers will be on the phone with their vet regardless of the size of their herd.”
“The best chance of identifying what caused an abortion is prompt submission of fetal and placental tissues and maternal blood or serum to a diagnostic laboratory,” Stokka said. “Contact your veterinarian for assistance with diagnostic efforts, sample submission and identifying management strategies to reduce the risk of future abortions.”
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