Heritable Birth Defects in Cattle
by Troy Smith for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 5, 2010) — An unintenced consequence of intensive selection for genetic improvement, genetic defects in beef cattle are being recognized at an increasing rate. During the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference, in Nashville, Tenn., Brian Whitlock of the University of Tennessee College of Veterinary Medicine discussed some of the more frequently occurring and economically important heritable abnormalities of cattle.
Whitlock said more than 360 genetic defects are known to exist among cattle. He noted how defects such as arthrogryposis multiplex (curly calf syndrome), neuropathic hydrocephalus and congenital contractural arachnodactyly (fawn calf syndrome) have occurred more frequently because intensive selection has resulted in a concentration of genes both good and bad. Certain individuals — typically sires that become popular for their desirable traits — have been used widely through technologies including artificial insemination (AI), thus distributing any unfavorable genes they also may carry.
Whitlock said not all birth defects are genetic. Some are caused by disease. Among those that are inherited, some result from gene mutations but many of the economically important abnormalities are autosomal recessive gene defects. These occur only when a carrier sire and carrier dam both contribute the recessive gene associated with a particular defect to their offspring.
Many such defects are lethal and result in a wasted pregnancy, Whitlock said. They often are accompanied by external as well as internal abnormalities, which cause dystocia. Some defects may also result in early embryo loss. Even when defects are non-lethal, affected animals generally do not perform satisfactorily and are of limited or no value.
According to Whitlock, molecular geneticists and veterinary pathologists have, with the cooperation of breeders and breed associations, identified numerous genetic disorders and developed DNA tests through which carriers can be identified. By identifying carriers and managing animals to avoid matings between carriers, defects can be controlled.
“As selection concentrates the genetics of certain individuals, the potential for emergence of heritable anomalies increases. The surveillance of such disorders has become an important part of bovine health programs,” Whitlock said.
For surveillance to be successful, recognition of a potentially heritable defect is only the first step, Whitlock added. It must be reported, appropriate samples collected and preserved, and pedigree information made available. Veterinarians can play an important role as well as producers. Whitlock also advised producers to make themselves familiar with known genetic defects and tests as they become available.
“Several diagnostic tests are available now,” Whitlock stated. “Utilize them.”
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