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Effects of Metoclopramide on Steers Grazing Endophyte-Infected Fescue^1,2,3,

University of Georgia, Athens 30602 and Southern Piedmont Conservation Research Center, Watkinsville 30677 and Auburn University, Auburn 36849

Abstract

The dopamine antagonist metoclopramide (MC) was administered to steers grazing on endophyte-infected fescue. Yearling Angus steers (n = 24) were assigned randomly to pasture treatments including high (74%) and low (33%) endophyte levels and low (134 kg N·ha^–1·yr^–1) and high (335 kg N·ha^–1·yr^–1) N fertilization rates. One steer of the pair in each paddock (n = 12) received MC, whereas the other received sucrose (S) (15 mg/kg body weight, orally, three times a week for 10 wk). Blood for basal and maximal TRH-stimulated serum prolactin (PRL) concentrations was obtained before animals grazed fescue, after grazing for 1 mo, and after 3, 6 and 9 wk of animal treatment. Grazing endophyte-infected fescue decreased (P < .05) basal serum PRL concentrations (<1.0 vs 5.3 ng/ml, high vs low endophyte). Basal serum PRL increased after 3, 6 and 9 wk of MC treatment (58.1 vs 5.4, 46.0 vs 12.0 and 50.8 vs 16.9 ng/ml, MC vs sucrose, respectively). After 6 wk of animal treatments, MC increased (P < .05) serum cholesterol (84.7 vs 60.8 mg/dl, MC vs S). Animals treated with MC spent more (P < .05) time between 1200 and 1600 grazing (22.4% vs 6.2%, MC vs S respectively) and had faster ADG (.314 vs .150 kg/d, MC vs S). The results implicate dopaminergic processes in fescue toxicosis.

¹ This research was supported by funds appropriated by the Georgia Vet. Med. Exp. Sta.

² The authors appreciate the use of facilities and equipment in the Anim. Physiol. Unit of Russell Res. Center, USDA/ARS, Athens, GA.

³ The authors acknowledge the skilled technical assistance of C. K. Smith, F. Hale, J. Saxon, D. Breedlove, M. Tabahdzade, D. Hildreth, and D. Belesky.

⁴ Dept. of Physiol. and Pharmacol., College of Vet. Med.

⁵ USDA, ARS, Watkinsville, GA 30677.

⁶ Dept. of Physiol. and Pharmacol., College of Vet. Med. and Anim. Health Res.