EFFECT OF SIMULATED RAIN, COAT LENGTH AND EXPOSURE TO NATURAL CLIMATIC CONDITIONS ON THE EFFICACY OF A TOPICAL FORMULATION OF EPRINOMECTIN AGAINST ENDOPARASITES OF CATTLE

A series of five controlled studies involving 114 cattle were conducte d in Australia, North America and the United Kingdom to examine the ef fect of simulated rain, coat length and exposure to natural climatic c onditions, on the efficacy of a topical formulation of eprinomectin ag ainst nematode parasites of cattle. In all trials infections were indu ced with a range of bovine nematode species and treatment was applied when the majority of nematodes were mature. In one study, simulated ra in was applied to cattle ending one hour before treatment or beginning one, three or six hours after treatment, In a second study cattle had short (1 cm) or long (3-6 cm) haircoats at the time of treatment. Thr ee other studies were conducted using cattle housed indoors or exposed to various natural climatic conditions. Nematode counts were determin ed using standard techniques and the efficacy of treatment was assesse d relative to vehicle-treated controls. Regardless of the timing of si mulated rain relative to treatment, eprinomectin was at least 99.9% ef fective (p <0.01) against Haemonchus placei, Ostertagia ostertagi, Tri chostrongylus axei and Cooperia spp. There were also no differences (p >0.10) in efficacy between treatment administered to dry or wet cattl e, or treatment administered before or after simulated rainfall, Effic acies against O. ostertagi, T. axei, Cooperia oncophora and Dictyocaul us viviparus were >99.5% (p <0.01) regardless of the length of the hai rcoat at the application site. Exposure of treated cattle to sunshine and precipitation had no effect on anthelmintic efficacy (p >0.10) wit h efficacies of greater than 99.5% being maintained against H. placei, O. ostetagi (adult and fourth-stage larvae), T. axei, Cooperia spp., Nematodirus helvetianus (adult and inhibited fourth-stage larvae) and Oesophagostomum radiatum. These findings indicate that eprinomectin (5 00 mu g/kg) in a topical formulation is a safe and highly effective ne matocide for cattle regardless of their coat length and this high leve l of efficacy is maintained in cattle exposed to a wide variety of cli matic conditions.