MUSCLE SPASMS ASSOCIATED WITH EAR TICK (OTOBIUS-MEGNINI) INFESTATIONSIN 5 HORSES

Severe muscle cramping not associated with exercise was observed in 5 horses. Focal muscle groups in various regions underwent intermittent visible contraction. Intermittent prolapse of the third eyelid, sweati ng, pawing, muscle tremors, and muscle fasciculations also were observ ed. Clinical signs often were misconstrued as signs of colic. Percussi on of muscle induced contraction of muscle groups. Concentrations of s erum electrolytes and the acid-base balance were within reference limi ts, but activities of creatine kinase and aspartate transaminase were moderately high. Muscle biopsy revealed no abnormalities except for a few necrotic muscle fibers undergoing phagocytosis. Electromyography o f 1 horse was suggestive of increased motor unit activity. All horses had Otobius megnini (ear tick) infestations and had recurrence of sign s until treatment was initiated for ear ticks.