Dr. Warren Bohnhoff, DVM

Now and in the past, the cause of cattle abortions has been difficult to diagnose. For years, Brucellosis, Leptospirosis, Bovine Viral Diarrhea (BVD), and Infectious Bovine Rhinotracheitis (IBR) were primarily thought to be the cause. Often, diagnostic tests proved these to be negative. The newest cause of abortions is being linked to Neospora.

Protozoa test discovered in California
Before the discovery of protozoa abortions in California, about 70 percent of all dairy cattle abortions, whether single cases or abortion storms, defied the best attempts at diagnosis. In California, pathologists and other researchers worked diligently in isolating a cause. The work progressed and received a push when California diagnosticians developed a new test using materials supplied by Dr. Dubey of USDA. The test made the protozoan parasite visible in the tissues being examined, thereby confirming that a Neospora-like agent was associated with a high number of abortions being investigated.

Protozoa abortions most commonly are identified at diagnostic laboratories in fetuses between four and seven months of gestation. Mummified fetuses are thought to occur if the fetal calf becomes infected with the protozoa at a specific stage of pregnancy.

Infected calves can be born
It's possible to have live births of congenitally infected calves with varying degrees of neurological symptoms or with no outward signs of infection. Aborting cows are not sick, and aborted fetuses usually do not have grossly visible lesions. Abortions may occur all year with a tendency for higher rates in late fall and early winter.

Calves have been found with precolostral titers, indicating infection moved from dam to calf during pregnancy. These same calves have maintained some level of antibody throughout a three-year research period. This indicates the parasite is not destroyed by the host's immune system and may persist for years within the tissues, possibly serving as a reservoir of the infection during later pregnancies.

Serum test show results
Herd surveys using serum test indicate most cows in some herds have been exposed to the protozoa agent, while in other herds there is no exposure. Research shows that cows positive to a serum test have twice the risk of abortion as negative herdmates. Also, dams with high titers are more likely to deliver live, but congenitally infected calves. Dams with low antibody levels are at highest risk to abort the infected fetus. Cows testing negative are more likely to deliver calves that are negative to a serum test.

Diagnosis
The best test results will come from sending an aborted fetus, as fresh as possible. Presently there are commercial and diagnostic labs offering serum and milk test for Neospora. Work closely with your veterinarian as test results can differ, depending on the test used. False positives and false negatives are possible.

Not all abortions from a positive dam are necessarily from this organism and not all abortions are necessarily caused by protozoa, even if protozoa are found in the fetal tissue. A new and promising ELISA test is now available which will help more closely determine the cause of abortion.