Causes and Prevention of Bovine Abortion

Abstract

Abortion is a particularly costly and vexing problem for veterinarians and cow/calf producers. Determining the causes of bovine abortion is difficult for several reasons, and despite the advances in diagnostic technology of the past few years, diagnostic success in bovine abortions seldom reaches 50% in laboratories around the world. Table 1 summarizes the results of diagnostic efforts on bovine abortions over the past 3 years at the South Dakota Veterinary Diagnostic Laboratory where specimens from 600 to 1000 aborted calves are examined each year. With the exception of dystocia, twinning, trauma, and anomaly (which in some cases may be caused by infection) all the causes listed are infectious, i.e. bacterial, viral, fungal, or protozoan. Because toxic, metabolic, and hereditary causes of abortion seldom result in a product or lesion readily recognizable in fetal tissues, these causes of abortion usually remain undetected by diagnosticians.

Obviously the stockman wants every pregnant cow to go to term and deliver a live, healthy calf. This is an unrealistic expectation, but the level of abortion in a herd that should elicit alarm has not been determined exactly. A maximum loss of 3%, while not desirable, probably is not unreasonable. Some of these losses may result from certain inherited hormonal deficiencies, and routine culling usually keeps this problem to a minimum. As with any average figure, this 3% loss does not occur uniformly each year in every herd. Therefore fewer than 1% "normal" abortions may occur in a herd for several years, and then the number may exceed 3% for 1 or more years. This makes it difficult to set a precise figure for the number of abortions that should be accepted before investigation into the cause is started, but in general, diagnostic efforts should be initiated any time more than 1% of the herd abort.