Recessive trait that causes extra limbs in Angus cattle identified, Neogen launches test


Cattlemen are hoping to weed out a newly discovered genetic defect in Angus cattle.

Developmental duplication, or DD, is a recessive defect that causes the calves to develop extra limbs (most commonly, extra front legs), a condition called polymelia. Calves affected by DD often die in utero. However, animals born with extra limbs can often flourish, especially if the additional limbs are removed, according to a report by Dr. Jonathan E. Beever, the University of Illinois researcher who identified the condition in Australian Angus cattle. It is worth nothing that cows giving birth to calves with DD can have difficulty, given the presence of the extra limb(s). Dr. Beever worked with Angus Australia and Dr. Laurence Denholm of the NSW Department of Trade and Investment.

Today, Neogen and Angus Genetics Inc. announced the availability of a genetic test for DD. Angus breeders can either submit new samples or use archived samples.

“Our experienced and dedicated team is able to provide consistent and rapid service on all of our DNA tests,” said Dr. Stewart Bauck, GeneSeek general manager, in a statement. “Improved DNA technology has allowed us to couple a variety of tests with our GeneSeek Genomic Profiler GGP-HD product as well, in a cost-effective manner.”

Dr. Beever began researching what eventually would come to be known as DD in 2011, after Angus Australia asked him to look into polymelia in in calves, which seemed to be increasing. Angus Australia has heard reports of about 20 cases of DD during the past four years. Polymelia has been observed in multiple cattle breeds, along with other animal species and even humans; however, the discovery of the mutation causing the extra limbs in Angus calves was the result of Dr. Beever’s research.

Following the announcement, the American Angus Association Board of Directors recognized DD as a genetic condition and set rules for testing and registration.

“Any animals identified as being homozygous for the mutation shall therefore be considered to be affected by the condition, and are not eligible for registration under Rule 103d,” the statement reads. “In the event that a registered animal is discovered to be affected by the condition, its registration shall be considered null and void, and the Certificate of Registration must be returned to the Association for cancellation.”

Selective breeding and genomics can help reduce or eliminate DD from the cattle population by breeding animals that don’t carry the recessive DD allele.

Genetics crash course

It all starts with alleles, which are different types of the same gene. In many organisms, including mammals such as cattle, each gene is made up of two alleles – one from each parent. A recessive allele only causes a visible trait (known as a phenotype) when the animal has two copies of the same allele (called homozygous). When paired with a dominant allele, the animal is considered heterozygous, meaning it has two different alleles. The animal will display the physical trait coded in the dominant allele. Although heterozygous animals don’t display the recessive trait, they still carry the recessive allele and can pass it along to offspring.

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