Breed Improvement
Genetic Defects By Jeff Hyatt - CSA Research Coordinator
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f you are involved in the cattle business you have likely heard of the term “Genetic Defect� and may automatically think of some type of terminal condition. However, the reality is that some genetic defects are either neutral or may even be beneficial to cattle. For example, the polled gene is a mutation of the horned gene, and that is a genetic defect that has made a massive and positive impact on the cattle industry. Expression of a defect can be as obvious as the horned/ polled gene or as invisible as a decrease in feed efficiency. So what is a genetic defect? It may be a deletion, mutation, movement, etc. of a portion of the genome. Most of the genetic defects that we deal with in the cattle industry are recessive mutations, where a portion of a gene is changed and only animals with both genes being recessive will actually physically express the defect. A dominant or homozygous mutation would cause all animals that had the defect to express the trait and if it was a lethal or detrimental trait, the animals would die or quickly be culled. In the example of a simple recessive genetic defect where only one gene affects the expression, an animal that is affected will have parents that are both carriers of the defect. If you were to mate a carrier to a normal animal, 50% of the progeny would be carriers and the other 50% would be normal. When mating two carrier animals, 25% of the progeny would be normal, 50%
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would be carriers and 25% would be affected by the trait. All breeds of beef cattle carry genetic defects and there have been animals that were imported from Europe that were later identified as carriers of detrimental genetic defects such as Cleft Palate, Cleft Lip, Syndactyly, Polydactyly, Arachnomelia, etc. Recently, an American herd had some cases of Arachnomelia, a malformation of the head, back and limbs, which all traced back to one common ancestor; through an identification process all of the carriers were removed from the herd voluntarily. Although all breeds have genetic defects, some breeds have more prevalent genetic defects then others and we are fortunate that these defects and the carriers of them are very few and far between within the Simmental breed when compared to other breeds. If an animal that carries Simmental genetics is suspected of possibly having a genetic defect, we encourage you to contact the CSA office to discuss the situation and we will work with you in going through the proper steps to deal with the suspected animals. If you have a calf born that looks like it may have a defect, take some pictures of the animal and pull hairs on the animal and then contact the CSA as soon as possible. This process is handled in complete confidence and is necessary to ensure that the Simmental breed remains as free from negative genetic abnormalities as possible.