COMPARISON OF THE PERSISTENT ACTIVITY OF IVERMECTIN, ABAMECTIN, DORAMECTIN AND MOXIDECTIN IN CATTLE IN ZAMBIA

The persistent efficacy of four commercially available macrocyclic lac tones (ML) in maintaining reduced faecal egg counts in cattle grazing naturally infested pastures was evaluated in 44 zebu animals aged 1-2 years in Zambia. The study started in February (rainy season) when the strongyle egg output was increasing, Four days before the start of th e trial, all animals were treated with a double dose of oxfendazole. T hey were then divided into five groups which were again treated on day 0. Groups A, D, I and M received 0.2 mg kg(-1) of abamectin, doramect in, ivermectin and moxidectin, respectively. Animals of group C receiv ed albendazole (7.5 mg kg(-1)). Faecal samples were collected twice a week for egg counts and larval differentiation. Faecal egg counts in t he C group increased from day 21 onwards and plateaued from day 42 bet ween 180 and 380 eggs per gram. The main genera found in cultures were Cooperia (90%) and Haemonchus (7%). Faecal egg excretion in groups M, A, D and I started on day 35, 42, 42 and 45, respectively. Subsequent ly and until day 84, average counts in these four groups were always s ignificantly lower than in group C, Compared with albendazole, all fou r ML gave over 95% reduction in cumulative faecal egg counts for 42 da ys after treatment. The percentage efficacy was still over 84% by day 84 when an average cumulative egg count of 11320 eggs per gram faeces was calculated in group C. In addition, there was no significant diffe rence in efficacy between the four ML groups at any of the sampling da tes. During the trial no significant difference in weight gain between any of the groups was observed. (C) 1997 Elsevier Science B.V.