Early-onset muscle weakness / MW / HMW (CACNA1S-related) - Cattle

Early-onset muscle weakness in Holstein cattle

This DNA test examines the CACNA1S variant c.3853G>A associated with early-onset muscle weakness in Holstein cattle. The condition is also known as MW, HMW, CACNA1S-related muscle weakness, calf recumbency or recumbency in calves.

What is seen in affected calves?

• Early onset: problems start in the neonatal period or during the first weeks of life.
• Muscle weakness: calves may be unable to stand without assistance or become recumbent again.
• Variable course: some calves are severely weak immediately after birth, while others become progressively weaker within the first six weeks.

Practical value of this test

The result helps Holstein breeders and breeding organisations distinguish clear animals, carriers and homozygous animals with genetic risk. Because carriers usually look healthy, DNA testing is the most direct way to identify the variant in breeding lines and avoid carrier pairings. The trait is inherited as autosomal recessive with incomplete penetrance, so genotype and clinical severity do not always match one-to-one.