AUTOSOMAL RECESSIVE MYOTONIA-CONGENITA IN SHEEP

Myotonia congenita in sheep causes episodes of muscular rigor followin g various stimuli. Episodes are transitory and do not harm the animal. Incidence in the flock of origin included three ewe lambs and three r am lambs. Two of the affected animals resulted from the mating of one specific unaffected ram to the unaffected daughters of a second unaffe cted ram. This mating produced 25 normal animals in addition to the tw o myotonic animals, which is consistent with the hypothesis of an auto somal recessive gene responsible for the condition, assuming the sire and maternal grandsire were the only ancestors carrying the gene (X-2 0.64, 1 df, P > 0.25). The four other affected animals had these two i ntroduced rams in their pedigrees on both maternal and paternal sides, suggesting that these two rams might indeed have introduced the gene into this flock.