Time profile of abamectin and doramectin excretion and degradation in sheep faeces

Abstract

We studied abamectin and doramectin excretion and their degradation in sheep faeces under field conditions on pasture after a single subcutaneous dose (0.2mg/kg body weight). In the excretion experiment, maximal abamectin concentration (1277ng/g dry faeces) was detected on day 3, while doramectin concentration showed two peaks (2186 and 1780ng/g dry faeces on days 2 and 5, respectively). Both avermectins were excreted at approximately the same rate (k=0.23day−1 for abamectin and 0.19day−1 for doramectin). In the field, a rapid loss of abamectin and doramectin from sheep faeces was seen during the first 32days after which concentrations remained constant at approximately 77ng/g and 300ng/g, respectively. The half life values (DT50) for abamectin and doramectin dissipation from sheep faeces were 23 and 22days, respectively, during the first 32days. Dissipation of both avermectins was strongly correlated with moisture content of the faeces.