Genetic research: University of Nebraska-Lincoln has identified a new genetic defect in cattle
Researchers at the University of Nebraska-Lincoln (UNL) have discovered a new defect in composite cattle – Simmental, Red Angus and Gelbvieh – which causes physical collapse when exercised and some calves may never recover.
This autosomal recessive genetic defect – meaning both parents of affected calves must carry one copy of the mutation – can affect the animal’s well-being and the quality of the meat they produce.
UNL Gudmundsen Sandhills Laboratory herd managers noticed calves from one to six months old lagging behind the herd when moving between pastures.
When the managers increased the calves’ pace, they would collapse and rest for brief periods of time.
A pedigree analysis revealed a standard herd bull in the sire pedigree of each affected calf, leading to the possibility of inbreeding.
This suggests a recessive genetic variant may be responsible for exercise intolerance in these calves.
The research
According to a May 28, UNL BeefWatch article by PhD Student Mackenzie Batt, the herd had undergone routine genotyping as part of the Integrated Beef Systems Initiative Genomics Infrastructure project, enabling a rapid genomic-based approach to finding the causative mutation.
“A genome-wide association study on 721 animals, including six affected calves and whole-genome sequencing on two affected calves pinpointed a significant region on chromosome 29,” she states.
“One mutation, not previously identified in this region, was predicted to truncate the protein product of the gene glycogen phosphorylase (PYGM). Due to the expected impact of this variant on the myophosphorylase protein encoded by PYGM and the identification of a previously discovered PYGM variant in Charolais cattle, this variant was prioritized for follow-up studies,” she adds.
Batt further notes 381 cattle, including eight affected calves, were genotyped for this variant, and in each case, both parents of the affected calf were found to carry one copy of the mutation. Each affected calf had two copies, as researchers expected for the recessive genetic variant.
Research conducted at UNL discovered the myophosphorylase encoded by PYGM plays a critical role in breaking down glycogen into usable energy, fueling muscles for sustained activity.
In conclusion, if myophosphorylase is absent, the glycogen breakdown will fail, leading to muscle damage and difficulties in physical activity. Affected calves showed a significant increase in glycogen stored in skeletal muscle, almost twice as much as normal and carrier animals.
“Additionally, affected calves had elevated creatine kinase before and after forced exercise,” she states. “This is an essential enzyme which aids in energy production during muscle contraction. Elevated creatine kinase is often a sign of muscle damage or stress.”
The research study also identified the calves experiencing twitching in their hind limbs and biopsies revealed visible signs of muscle damage.
Despite muscle-related issues, microscopic examination of other organs revealed no abnormalities.
The research team discovered myophosphorylase protein in healthy animals but missing in affected calves.
Advancement in genetics
“This result aligned with an additional test, where specific antibodies were used to identify the PYGM protein in the muscle, where a normal calf displayed a positive result with red pigmentation while affected calves distinctly lacked the PYGM protein,” Batt states.
The inability to efficiently break down glycogen compromises the well-being of the animals and negatively impacts the quality of the meat they produce.
She reiterates, “Breaking down stored glycogen efficiently after an animal is harvested is crucial for making high-quality beef.”
In the absence of myophosphorylase, glycogen breakdown is restricted, hindering the expected decrease in pH and changing the meat’s color to dark red.
“Mutations in the same gene in humans result in a disease similar to what is observed in these cattle, termed McArdle disease,” Batt continues. “Individuals with McArdle disease experience muscle fatigue and weakness during physical activities but can adjust diet and exercise and live a normal life.”
However, these adjustments are not practical or achievable when raising cattle for production, plus the economic benefits of managing this condition in cattle is limited.
“This recessive condition significantly affects muscle metabolism, raising concerns about animal welfare and introducing economic challenges in raising livestock,” Batt says. “These repercussions can affect the survival of animals and, subsequently, the quality of the meat they produce at harvest.”
She notes this study stands out as one of the initial efforts to pinpoint a specific genetic mutation linked to this condition, paving the way for future research into the genetics of dark-cutting beef.
This comprehensive research study is crucial for the well-being of beef cattle and assures quality of the final product.
This collaborative effort involved UNL students and faculty across disciplines, including graduate student researchers. The full paper was published in BMC Genomicss and is available at link.springer.com/article/10.1186/s12864-024-10330-1#citeas.
Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
