Ask the Vet

Common Causes of Abortion in the Cow Herd

Causes of calf abortions in cow herds vary regionally. (DTN/Progressive Farmer file photo)


We raise cattle in Tennessee. We have been having issues with abortions in our fall-calving herd. This past fall we had three abortions. All of our heifers get two rounds of a modified IBR, BVD, PI3, BRSV with Lepto. The whole herd gets VL5 once a year. We have a hay field that we mow for a first cutting, but we use it as pasture after that. That seems to be when our problems started. Could the abortions be caused by something they are eating?


Certainly, there are plants that can induce abortion. Ponderosa pine needles, locoweed, broom snakeweed, moldy sweet clover and many grasses and weeds that accumulate nitrates have been linked to abortions in cattle. That said, infectious agents are actually the most commonly identified causes.

Even in the best-managed herds, a 1% to 2% abortion rate is considered normal. Some have even suggested 5% as an acceptable rate, but I get concerned about anything over 1%. Each producer must decide when abortions need aggressive investigation.

Ideally, when an abortion takes place, the fetus and placenta should be submitted to a diagnostic laboratory for testing. Labs may use different testing protocols, but often include histopathology (microscopic exam of tissues), bacterial culture, viral isolation, PCR testing, and others. Paired serum samples two to four weeks apart are often used to identify changing tiers of viral, bacterial, and protozoan pathogens.

Even with this approach, diagnosis of the cause of an abortion is difficult. Abortions often follow an event that occurred weeks or months prior, and as a result, what caused the abortion may no longer be detectable. Toxic, nutritional, hormonal, and genetic causes are often not detectable in fetal tissues. Additionally, the fetus is often in an advanced state of decay, making testing difficult at best. The placenta, which is extremely valuable in making a diagnosis, is often not found or submitted. I have never seen any study where a cause was found in over 50% of the cases, and most report finding the cause about 20% to 30% of the time.

In one study of almost 3,000 cases done in South Dakota, the most common causes were nonspecific placentitis (28%), pus-forming bacteria (6%), fungal/mucotic (3%), IBR virus 3%, nonspecific bacteria (2%), Neospora (1%) and other "other" (4%). That left 53% with no diagnosis. Another large study from California found a much higher incidence of Neospora, a protozoan parasite. This makes clear that causes of abortions vary by location.

So, back to what to do. Your vaccine program looks very reasonable. Since you are concerned about this one hay field, I would soil test it and apply fertilizer and lime as needed. Chemical control of weeds would also be indicated. These are solid management practices that will pay dividends in any case. Any other changes to management or your vaccine program should be strictly based on consultation with your herd veterinarian and on any lab results you have available to you.


Editor's Note:

Please contact your veterinarian with questions pertaining to the health of your herd or other animals. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice but is purely for informational purposes.

Write Dr. Ken McMillan at Ask the Vet, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email