A PRELIMINARY-STUDY OF THE EFFICACY OF FLUPHENAZINE AS A TREATMENT FOR FESCUE TOXICOSIS IN GRAVID PONY MARES

This study was designed to determine the efficacy of a single injectio n of the long-acting D-2-dopamine receptor antagonist, fluphenazine de conoate, on the clinical symptoms and plasma prolactin concentrations of mares grazing endophyte-infected tall fescue. Twelve mares were mai ntained on an 80% endophyte-infected tall fescue pasture. Group T (n = 6) received 25 mg of fluphenazine deconoate i.m. on day 320 of gestat ion, while group C (n = 6) served as untreated controls. Daily plasma samples were obtained and analyzed for prolactin using a homologous eq uine radioimmunassay. The prolactin data were then grouped according t o week after treatment (day 320 to 327 = Week 1; day 328 to 335 = Week 2) and to week prior to parturition (day 0 to -7 = Week -1; day -8 to -14 = Week -2). A single injection of fluphenazine had no effect on e xperiment-wide plasma prolactin concentrations or on prolactin concent rations relative to week of treatment or parturition. However, a treat ment by time period interaction was observed. Plasma prolactin concent rations were higher (p < .05) in treated mares (35.6 +/- 29.1 ng/ml) o n week 2 compared to control mares (14.9 +/- 14.2 ng/ml). In addition, there was a trend (p = .09) for fluphenazine treated mares (68.1 +/- 64.2 ng/ml) to exhibit higher prolactin concentrations one week prior to parturition when compared to control animals (27.8 +/- 27.4 ng/ml). Peak prolactin was higher (p < .05) in fluphenazine treated mares and in mares which foaled normally. Gestation lengths were shorter (p < . 05) in group T (330 +/- 2.9 days) compared to group C (341 +/- 3.2 day s). It appeared that treated mares exhibited fewer clinical signs of f escue toxicosis than mares in group C. Four out of six of the untreate d mares exhibited at least one of the clinical signs of fescue toxicos is (agalactia, stillbirth, thickened placenta, retained placenta) whil e only one treated mare showed obvious clinical symptoms. These data i ndicate that a single injection of a long-acting dopamine receptor ant agonist may be beneficial in reducing the effects of fescue toxicosis in pregnant mares grazing endophyte-infected tall fescue pastures. How ever, additional research is needed to determine the most effective do sage and administration times.