A variety of clinical neurological syndromes exists in stocker and feeder cattle. Causes may be infectious, nutritional/metabolic, or toxins. A less common syndrome is referred to as "nervous" coccidiosis, named so because of the observation that many of the calves that experience this neurological syndrome concurrently exhibit clinical enteric coccidiosis.(1) This entity was first reported in 1921.(2)
Nervous coccidiosis can occur at any time of the year but appears most often in the fall and early winter, coinciding with the time of the year when many calves move to feedlots. This syndrome reportedly can occur in up to 30% of the calves affected with enteric coccidiosis. As many as 10,000 cattle die annually in the U.S. from this problem. The pathogenic mechanisms for nervous coccidiosis, however, are not clearly resolved.(1) Coccidial organisms or microscopic lesions consistent with coccidial infection cannot always be found in affected calves.(3) Researchers have not been able to experimentally reproduce this syndrome. The absence of significant brain lesions eliminates infectious and some nutritional factors and toxic agents as primary causes.(1)
Clinical signs of nervous coccidiosis may vary in severity and frequency and may range from minor muscular incoordination, twitching, and loss of balance to intermittent or continuous seizures. During seizures, affected calves collapse into lateral recumbency and exhibit a variety of signs, including opisthotonos, tetany, medio-ventral strabismus, nystagmus, paddling movements, exaggerated snapping of the eyelids, salivation, star gazing, nervousness, occasional bellowing, and rapid and irregular respiration. Affected calves may get up and experience periods of apparent normalcy between seizures. Seizures often recur when the calves are stressed or handled.
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