New genetic insight in beef cattle

By Scout Nelson

A recent breakthrough at the University of Nebraska — Lincoln has led to the discovery of a significant genetic defect in cattle, specifically in breeds such as Simmental, Red Angus, and Gelbvieh. This defect, linked to poor muscle function and reduced meat quality, poses a challenge for cattle health and beef production.

Researchers observed that affected calves exhibited exercise intolerance, often collapsing during movement. This condition stems from an autosomal recessive genetic mutation, necessitating that both parent cattle carry the defective gene.

This defect impacts the PYGM gene responsible for producing myophosphorylase, an enzyme crucial for converting glycogen into energy in muscle tissues.

The discovery was facilitated by the Gudmundsen Sandhills Laboratory’s routine genotyping practices, part of the Integrated Beef Systems Initiative. Through comprehensive genetic analysis, including a genome-wide association study and whole-genome sequencing, researchers pinpointed the mutation on chromosome 29.

This defect leads to a significant accumulation of glycogen in the muscles, nearly double that of normal and carrier animals, and elevated levels of creatine kinase, indicating muscle stress or damage. Muscle biopsies from affected calves showed visible damage, although other organs appeared normal under microscopic examination.

The lack of efficient glycogen breakdown not only affects the cattle’s physical capabilities but also the quality of beef produced. Meat from affected cattle does not decrease in pH as expected after slaughter, resulting in a darker, less desirable meat, known as dark-cutting beef. This issue is critical as it affects the meat's appearance, shelf life, and market value.

The situation mirrors McArdle disease in humans, where individuals experience muscle fatigue and cannot efficiently manage physical activities requiring sustained effort. While humans can adapt lifestyle and diet to manage the condition, such adaptations are impractical for cattle.

This genetic discovery is crucial for the cattle industry as it allows for better breeding decisions to avoid producing affected calves. By understanding and managing this genetic condition, farmers and breeders can enhance animal welfare and ensure the quality of beef, thereby minimizing economic losses. This study paves the way for further research into the genetics of meat quality and cattle health.

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