Techical Keynote Session 1

Selection Against Genetic Defects Utilizing Inbreeding, DNA Markers

By Troy Smith

During the past few years, cow-calf producers have gained new awareness of genetic defects and how diagnostic tests for such defects can be developed through DNA technology. A good example of practical application is the DNA test developed for the recessive gene associated with arthrogryposis multiplex (AM), or curly calf syndrome.

During technical committee discussions at the 2009 Beef Improvement Federation (BIF) symposium, geneticist Mark Thallman said there has been essentially no emphasis, however, on development of a systematic approach to identifying and eliminating genetic defects before they become serious problems. Thallman, a scientist at the U.S. Meat Animal Research Center (USMARC), Clay Center, Neb., said DNA tests typically are developed after defects occur with enough frequency to make serious economic impacts.

“Our current approach is to ‘put out fires’ by using DNA tests to reduce the frequency. But wouldn’t it be better to discover defects before they occur with high frequency?” Thallman asked. “I submit that selection against recessive genetic defects could be accomplished through a combination of inbreeding and DNA-marker technology.”

Systematic progeny testing proposed

Thallman proposed to identify recessive defects in influential sires and select against them through DNA testing of the sires’ descendants. Once defects have been effectively reduced among the elite segment of the population, Thallman predicts occurrence of defects in the whole population should rapidly diminish.

Based on progeny performance, sires expected to be used extensively for artificial insemination (AI) would be selected to produce inbred progeny. The proposed strategy calls for breeding a young sire to enough females to produce 25 to 50 progeny. If the sire is a carrier of a recessive defect, two to four of the resulting progeny should display the defect.

The affected progeny would then be used to identify DNA markers for genes associated with each discovered defect, which could be applied to manage selection. Occurrences of a defect could be avoided by not mating carrier bulls with carrier females.

The system could reveal additional defects, as well as differences in performance that we may not call defects but that do affect profitability, Thallman said.

“I’m suggesting a proactive approach,” Thallman stated. “However, this will require a transition toward a less emotional and more pragmatic paradigm for managing genetic defects.”

Editor’s Note: This summary was written under contract or by staff of Angus Productions Inc. (API). To request reprint rights contact Shauna Rose Hermel, editor, at 816-383-5270. PowerPoints are posted with permission of the presenter and may not be reproduced in whole or in part without the express permission of the presenter.

The 41st BIF Research Symposium and Annual Meeting was hosted by the California Beef Cattle Improvement Association and the California Cattlemen's Association. For more information, visit www.bifconference.com or www.calcattlemen.org/bif2009.html.