THE DEGRADATION OF DUNG PRODUCED BY CATTLE TREATED WITH AN IVERMECTIN SLOW-RELEASE BOLUS

Eight female calves of the Deutsches Fleckvieh breed, weighing 161-207 kg, were each treated at turnout on 16 May 1989 with one ivermectin sustained-release intraruminal bolus designed to release ivermectin at 12 mg day-1 for approximately 120 days. Eight animals remained as untreated controls. A third group of eight unmedicated tracer calves was not considered as part of this evaluation. All 24 animals grazed together on a single pasture throughout the study. On Days 21/22, 70 and 119, 15 faecal pats were selected from each treatment group and ranked according to surface area; within each group of three consecutively ranked pairs of pats, two pairs were randomly allocated as observation pats and the third as a sampling pat. The surface area of observation pats was measured, photographs taken, and dry matter, crude ash and organic matter determined at various intervals following deposition. A 1/4 sample collected from sampling pats 3, 7, 14 and 28 days after deposition was weighed and examined for Coleoptera (adults and larvae), Diptera larvae and nematodes. No differences between groups were seen in respect of organic matter content, numbers or frequency of adult Coleoptera species and soil nematodes. A decrease in numbers of Coleoptera larvae, Diptera larvae and dung-specific nematodes was observed in pats from ivermectin-treated cattle. Based on the evaluation of the surface area, a delay in the degradation rate of pats from treated compared with those from untreated animals was seen; however, the difference was statistically not significant (P>0.05).