EFFICACIES OF DIFFERENT DOSES OF IVERMECTIN AGAINST MALE, FEMALE AND L4 OESOPHAGOSTOMUM-DENTATUM IN PIGS

Efficacies of ivermectin against larval stages and adult males and fem ales of Oesophagostomum dentatum were investigated in two slaughter as says. In Experiment A, 20 pigs were each infected with 6000 third-stag e larvae on Day 0 and Day 24. Pigs were ivermectin treated on Day 28 a t dose rates of 0, 75, 150 and 300 mu g kg(-1) bodyweight (bw) and sla ughtered 6 days after treatment. in Experiment B, 20 pigs each receive d 6000 third-stage larvae and were treated 35 days after infection at dose rates of 0, 150, 300 and 600 mu g kg(-1) bw, Pigs were slaughtere d 14 days after treatment. In Experiment A, the adult worm burden was reduced by 69.1% at a dose rate of 300 mu g kg(-1) bw and the larval b urden was reduced by 68.7 and 90.9% at 150 and 300 mu g kg(-1) bw, res pectively, In Experiment B, the adult worm burden was reduced by 88.8, 96.2 and 99.6% at dose rates of 150, 300 and 600 mu g kg(-1) bw, resp ectively, In the control group of Experiment A, the mean proportion of females among adult worms was 57.6%, but this decreased to 19.7% afte r ivermectin treatment at 300 mu g kg(-1) bw. In Experiment B, at 300 mu g kg(-1) bw, this proportion was reduced from 46.0% to 0.8%. The fe cundity of female worms was reduced at dose rates of 150 and 300 mu g kg(-1) bw in Experiment A, but not in Experiment B, It is concluded th at in O. dentatum, ivermectin not only reduces the egg output of femal e worms, but also is more effective against female than male worms.