Abstract:

Objective Early onset muscle weakness syndrome （MW） is a recently discovered genetic defect in Holstein cattle. The sick calves exhibit symptoms such as lying down motionless after birth and atrophy of the hind limb muscles. Its genetic mechanism is related to a single-base mutation in the gene CACNA1S， which encodes the α1S subunit of the L-type calcium channel protein. This study aimed to establish a molecular detection method for this genetic defect and explore its spread within the Chinese Holstein cattle population. Method Based on the specific DNA sequence of MW pathogenic site， the primers were designed for amplification refractory mutation system PCR （ARMS-PCR）. A genetic defect gene screening was conducted on 317 samples of Holstein bull frozen semen and hair follicles， and the results of ARMS-PCR were verified through Sanger sequencing. Pedigree data was used to trace the source of the MW mutation. Result ARMS-PCR detected 21 carriers of MW mutation with a carrier rate of 6.62% （21/317）， and no pure heterozygotes for the defective gene were found， suggesting that the mutation was recessive and purely lethal. Sanger sequencing showed the consistent genotypes with those obtained by ARMS-PCR， demonstrating the high accuracy of this technique. Furthermore， pedigree analysis traced the origin of MW carriers to the Holstein bull Southwind Bell of Bar-Lee， born in 1984. Conclusion The MW genetic defect had already spread within Chinese Holstein cattle populations and was present at a relatively high frequency. It was recommended that ranchers should carry out genetic testing and risk assessment of MW genetic defects as early as possible， and take scientific selection and mating measures to effectively reduce the economic losses caused by genetic defects.

Key words: early onset muscle weakness syndrome （MW）; ARMS-PCR; genetic testing; genetic defect; Sanger sequencing