EFFICACY OF A POUR-ON FORMULATION OF EPRINOMECTIN (MK-397) AGAINST NEMATODE PARASITES OF CATTLE, WITH EMPHASIS ON INHIBITED EARLY 4TH-STAGELARVAE OF OSTERTAGIA SPP

Objective-To evaluate efficacy of topically applied eprinomectin again st inhibited early fourth-stage larvae (IL(4)) of Ostertagia spp in ca rves. Animals-4 groups (n = 6 [replicates]) for dose titration; 2 grou ps (n = 8 calves [replicates]) for dose confirmation. Procedure-2 dose titration studies-0, 125, 250, and 500 mu g of eprinomectin/kg of bod y weight-Louisiana and Georgia-and 2 dose confirmation studies of sele cted therapeutic dosage (500 mu g/kg) in Scotland and France. Monitor calves were used to determine inhibition percentage of Ostertagia IL(4 ). Test calves were ranked by weight in replicates of 4 (titration tri als) or 2 (confirmation trials) animals each, and within replicates, w ere randomly allocated to treatment groups. Drug treatments were done on day 0, and animals were euthanatized by replicate, with holding tim e between treatment and euthanasia varying among trials from 14 to 27 days. Results-Observations indicated high efficacy (> 99%) of 500 mu g of eprinomectin/kg in removal of Ostertagia IL(4). Ostertagia and Coo peria were only genera common across sites, with efficacy of aforement ioned dosage against adult and larval stages of both genera consistent ly high (> 99%). Results of 1 or both titration studies (500 mu g/kg) indicated > 99 to 100% efficacy against adult Haemonchus placei, Trich ostrongylus axel, T colubriformis, Bunostomum phlebotomum, Dictyocaulu s viviparus, and Oesophagostomum radiatum. Lower efficacy values were observed at minimal (125 mu g/kg) dosage. In France, 500 mu g/kg was 8 5% effective against Trichostrongylus spp adults; however, numbers of control calves infected with Trichostrongylus spp and degree of infect ion were low. Adverse reactions were not evident. Conclusion-Eprinomec tin given topically (500 mu g) was highly effective against Ostertagia IL(4) and other common nematodes of cattle.