THE EFFECT OF FECALLY EXCRETED IVERMECTIN AND FENBENDAZOLE ON THE INSECT COLONIZATION OF CATTLE DUNG FOLLOWING THE ORAL-ADMINISTRATION OF SUSTAINED-RELEASE BOLUSES

The effects of faecal drug residues following the administration of an thelmintics in the form of sustained-release boluses, on dung-colonisi ng Coleoptera and Diptera are reported. In blind field trials, pats of standard weight and size were prepared from the dung of cattle treate d with an ivermectin (Ivomec SR Bolus(R), MSD Agvet) or a fenbendazole (Panacur Bolus(R), Hoechst) sustained-release bolus, and from a third control group of cattle that received no treatment. Fats were recover ed after 7, 14, 21 and 42 days in the field and searched for invertebr ates. There were no differences in the numbers of adult beetles found in the pats from the three treatment groups. Fats made from the dung o f ivermectin-treated animals contained no larval Diptera Cyclorrhapha and significantly fewer larval Scarabaeidae than pats made from the du ng of the other two groups. Furthermore, larval Scarabaeidae in the iv ermectin pats were inhibited in their development. The pats from fenbe ndazole-treated animals contained similar numbers of larval Scarabaeid ae and Diptera to the pats from untreated animals throughout the trial . At 42 days, the solid matter of the control and fenbendazole-contain ing cow pats was reduced to a crumbling, granular texture, while the p ats from the ivermectin-treated animals were solid and compacted. Pitf all trapping, using traps baited with dung from the three groups, show ed no significant difference between the numbers of adult Scarabaeidae attracted, though a trend towards higher numbers attracted to the dun g of both anthelmintic-treated groups was evident. The results provide evidence of the toxic effects of excreted ivermectin on key dung-colo nising families of insects, and show that fenbendazole lacks such toxi c effects.