Caprine Myotonia

Myotonia congenita in goats is due to an autosomal dominant mutation in the skeletal muscle chloride channel that has incomplete penetrance. Goats with this mutation have been selected for as a breed and are commonly referred to as “fainting goats.” Clinical signs ranging from stiffness after rest to marked general rigidity after visual, tactile, or auditory stimulation usually develop by 6 wk of age. These signs remain throughout the animal's life but are not progressive. A diagnosis of myotonia is made by identifying the characteristic “dive bomber” discharges in electromyography and/or by genetic testing.

Phosphorylase Deficiency in Charolais Cattle

A mutation in the myophosphorylase gene in Charolais cattle produces signs of exercise intolerance and muscle necrosis very similar to nutritional myodegeneration. The disease has now been recognized in many countries including the USA and New Zealand. Animals become exercise intolerant may collapse when forced to exercise and develop muscle necrosis characterized by elevated serum CK and prolonged recumbency. Supportive care during episodes has allowed many young animals to survive and unknowingly enter the breeding herd.

Porcine Malignant Hyperthermia

Malignant hyperthermia in swine (see Malignant Hyperthermia) is due to an autosomal recessive genetic mutation in the skeletal muscle ryanodine receptor 1gene (RYR1) that causes abnormal meat quality in swine. Pietrain, Poland China, and certain strains of Landrace pigs are affected. During transportation or anesthesia, pigs develop elevated body temperature, extreme rigidity of the skeletal muscles, and lactic acidosis. At slaughter affected muscles become pale, soft, exudative muscle, which diminishes meat quality. A genetic test is available to diagnose affected and carrier animals.

Porcine RN (–) Glycogen Storage Disease

The RN(−) (rendement Napole) phenotype is common in Hampshire pigs. It is due to an autosomal dominant mutation in the protein kinase AMP-activated gamma 3 subunit gene (PRKAG3), which encodes the gamma 3 isoform of AMP-activated protein kinase (AMPK). Clinically pigs appear normal; however, the 70% increase in glycogen content in skeletal muscle causes poor meat quality at slaughter.

Last full review/revision March 2012 by Stephanie J. Valberg, DVM, PhD, DACVIM