DORAMECTIN EFFICACY AGAINST GASTROINTESTINAL NEMATODES IN PIGS

Four controlled trials with growing pigs were performed to determine e fficacy of doramectin against natural and induced populations of nemat odes. In Trial I (T1), 20 pigs with natural infections were assigned t o one of two like groups on the basis of weight, sex and worm egg coun ts. In Trial 2 (T2), 20 pigs with negative worm egg counts were assign ed to one of two groups on the basis of weight and sex. Each pig was s ubsequently given (per os) 3000 Trichuris suis embryonated eggs; 2000 Ascaris suum embryonated eggs; 10000 Oesophagostomum spp. infective la rvae and 10000 Strongyloides ransomi infective larvae (SC injection). In Trial 3 (T3), 20 pigs with negative worm egg counts were assigned a s in T2, and each pig was subsequently given (per os) 2000 A. suum emb ryonated eggs, 15000 Oesophagostomum quadrispinulatum infective larvae , and 2891 Hyostrangylus rubidus infective larvae. In Trial 4 (T4), 16 pigs with negative worm egg counts were each assigned to one of two g roups as in T2 and were given (per os) 2670 T. suis embryonated eggs. On Day 0 of each trial, each pig of the contol group was injected IM i n the neck with sterile saline at the rate of 1.5 mi 50 kg(-1). Each p ig in the treated group of each trial was similarly injected with dora mectin at the rate of 300 mu g kg(-1). Ail pigs were necropsied 14 or 15 days post-treatment and parasites recovered by standard parasitolog ical procedures. Efficacies against natural infections were: A. suum, 100%; Oesophagostomum spp. 100%; H. rubidus, 99.4%; and Strongyloides ransomi, 99.9%. Efficacies against induced infections were: 4th stage A. suum, 100%; 4th stage O. dentatum, 99.9%; 4th stage O.quadrispinula tum, 97.1 and 99.6%; 4th stage H. rubidus, 100%; adult S. ransomi, 100 %; adult Trichuris suis in mixed infection, 54.1%; and in pure infecti on, 95.3%.