American Angus Association recognizes new genetic condition
The American Angus Association (AAA) now recognizes Developmental Duplication (DD) as a genetic condition. This simple recessive trait causes the majority of the calves exhibiting DD to be born with additional limbs.
According to Jonathan Beever, professor of animal science at the University of Illinois at Urbana-Champaign, the duplication is typically of the front legs and originates in the neck and shoulder region.
With the exception of mortality and calving difficulty, calves with DD often thrive. The extra limbs can be surgically removed.
“The allele frequency among U.S. sires is moderately high, at approximately three percent. This corresponds to the carrier frequency of approximately six percent,” Beever says in his analysis of sires.
“The study also showed that no homozygous individuals are present in the population,” he continues. “Of course, one would not expect a calf born with five or six legs to become an AI sire. However given the moderate allele frequency, the rarity of affected calves, particularly as reported in the U.S., is somewhat puzzling.”
“Additionally, given the use of specific U.S. sires, now known to be carriers, the frequency of reported calves is also unexpectedly low,” Beever explains. “Thus, we believe these data indicate that calves presenting with polymelia, or additional limbs, at birth are rare events that survive embryonic death.”
The newly adopted policy from the AAA Board of Directors states that producers are not mandated to test potential DD carriers as a precondition of continued or perspective registration.
A letter released by the Board to producers states that they will assume members will make strategic use of DNA testing in dealing with this genetic condition and follow sound breeding decisions.
“There are alternatives to mandatory testing, and over the past five years, our members have shown a willingness to embrace them,” the letter from the Board says. “These include a better understanding and acceptance of the ability to manage around a known genetic condition by avoidance of breeding carrier to carrier and by the use of voluntary, strategic DNA testing. Equally important, our commercial breeders also understand and embrace these management principals.”
Angus sires are currently being tested to determine if they are carriers of the allele. An updated list of sires and their test results can be found at angus.org/Pub/DD/DD_Update08122013.pdf.
Angus Genetics, Inc. and GeneSeek have developed a test for DD using DNA samples. The sample types include dried blood, hair, semen, blood tube and tissue samples.
The preferred method requires a blood sample to be drawn out of the ear of the animal and allowed to coagulate on the card prior to mailing.
Hair samples are required for testing twins. The sample should include a minimum of 20 hairs from the tail switch that have the root bulb attached. Samples must have the root bulb to be a viable sample. Clipped samples will not yield genetic results.
Additional sample methods include a semen sample and blood tubes.
Thawed semen straws should be taped between cardboard pieces or placed a tube to avoid crushing the sample. Samples should be sent at room temperature.
Blood tube samples filled with six to nine milliliters of blood will also yield genetic results. However, an additional sample fee will be charged with this method. The samples should be shipped overnight with a cold pack in an insulated container.
Tissue samples can be used to determine if a deceased animal was a carrier. Producers should contact the testing company to obtain instructions for testing.