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Paspalum Staggers

By Gary D. Osweiler, DVM, MS, PhD, Professor Emeritus, Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University

This incoordination results from eating paspalum grasses (Paspalum spp) infested by Claviceps paspali. The life cycle of this fungus is similar to that of C purpurea (see Ergotism). Toxic infestations are most likely after humid, wet summers. The yellow-gray sclerotia, which mature in the seed heads in autumn, are round, roughened, and 2–4 mm in diameter. Ingestion of sclerotia causes nervous signs in cattle most commonly, but horses and sheep also are susceptible. Guinea pigs can be affected experimentally. The toxicity is not ascribed to ergot alkaloids; the toxic principles are thought to be paspalinine and paspalitrem A and B, tremorgenic compounds from the sclerotia.

A sufficiently large single dose causes signs that persist for several days. Animals display continuous trembling of the large muscle groups; movements are jerky and incoordinated. If they attempt to run, they fall over in awkward positions. Appetite remains good, and animals will eat if feed is provided. Affected animals may be belligerent and dangerous to approach or handle. After prolonged exposure, condition is lost and complete paralysis can occur. The time of onset of signs depends on the degree of the infestation of seed heads and the grazing habits of the animals. Experimentally, early signs appear in cattle after sclerotia at ~100 g/day has been administered for >2 days. Although the mature ergots are toxic, they are most dangerous just when they are maturing to the hard, black (sclerotic) stage.

Medical treatment is usually not necessary, unless animals have physical injuries or are compromised from dehydration or lack of eating. Recovery follows removal of the animals to feed not contaminated with sclerotia of C paspali. Animals are less affected if left alone and provided readily available nutritious forages. Care should be taken to prevent accidental access to ponds or rough terrain where accidental trauma or drowning could occur. Topping of the pasture to remove affected seed heads has been effective in control.