CM is Congenital Myotonia - it is a recessive disease
Myotonia slows the relaxation of muscles after voluntary contraction or electrical stimulation this shows up as difficulty rising to the horses feet, abnormal vocalization, a stiff gait, and rigin dlimbs, neck and trunk.
Myotonia has been found in the New Forest Pony.
There is no effective treatment.
Genetic Testing is available.
Genetic Codes:
N/N The horse is normal, and cannot produce affected offspring.
N/cm This horse carries CM and will pass the allele on to approx. 50% of its foals. If bred to another N/cm carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
cm/cm The horse is affected with congenital Myotonia and will pass one copy of CM to every foal.