EFFICACY OF AN IN-FEED FORMULATION OF IVERMECTIN AGAINST ADULT WORMS AND SOMATIC LARVAE OF STRONGYLOIDES RANSOMI

The efficacy of an in-feed formulation(IVOMEC(R) premix) containing 0. 6% ivermectin was tested against Strongyloides ransomi in swine. The e fficacy of ivermectin against patent infections of S. ransomi when giv en via the feed at 2 ppm for 7 days (Days 0-7) to provide 100 mcg iver mectin kg(-1) body weight day(-1) was evaluated in a study with 16 3-m onth-old male castrated piglets, Seven days prior to treatment each pi glet was infected subcutaneously with 2500 infective larvae of S. rans omi. Fecal egg counts were carried out on Days -7, 0, 7 and 14, and wo rm counts on Day 14, Efficacy was 100% in all treated piglets. Two tri als involving 40 pregnant gilts were carried out to evaluate the effic acy of ivermectin against the somatic larval stages of S. ransomi when given at a daily dose of 100 meg kg(-1) body weight for 7 days starti ng on Days 66, 78, 92 or 103 of pregnancy. The gilts were each experim entally infected with three subcutaneous injections of 250000 infectiv e larvae, with the last infection given between 12 and 30 days prior t o commencement of treatment. Gilts were confirmed free of pre-existing intestinal stages of S. ransomi prior to ivermectin treatment. Fecal nematode egg counts were carried out in gilts/sows and piglets subsequ ently born, The Strongyloides larvae present in sow milk 1, 2 and 7 da ys post partum were counted, Fourteen days post natum, worm counts wer e performed in four randomly selected piglets from each litter. IVOMEC (R) premix given to pregnant gilts prevented shedding of larvae in sow milk, egg output in feces and the establishment of S. ransomi in pigl ets.