Lucija Kolar

Factors influencing dissipation of avermectins in sheep faeces

Factors influencing fate of avermectins (abamectin, doramectin) in faeces of treated sheep were investigated under different experimental conditions. In the laboratory, concentrations of both avermectins were declined in homogenised faeces of treated animals until day 14 of exposure, regardless of experimental conditions. After that day, no significant decrease in concentrations was observed till the end of the experiment. Established DT(50) did not exceed 9 days. In the karst pasture, an average DT(50) of 27 days was established for abamectin and 23 days for doramectin in natural faeces of treated sheep. In the compost mixture, doramectin concentration was decreased by 38.9+/-2.6% during 21 days of the thermophilic phase of composting. Therefore, DT(50) was not established. A possible influence of moisture content of sheep faeces on concentrations of avermectins was observed.

Degradation of abamectin and doramectin in sheep faeces under different experimental conditions

Avermectins is the collective name given to a range of animal health products used in the prevention of parasitosis. Residues of these drugs retain their insecticidal properties after excretion in livestock faeces. We investigated the degradation of abamectin and doramectin in sheep faeces under the laboratory and field conditions. In the first two, out of three experiments, we exposed collective abamectin or doramectin contaminated and homogenised faeces samples to laboratory (UV light; l = 370 nm) and to field conditions on sheep pasture (exposed on the plate or put directly on the soil). The third experiment focused on degradation of both avermectins excreted via sheep faeces directly to the pasture. The degradation of both substances was evident in both cases, either under laboratory or under field conditions. The results show that degradation process is affected by physical properties of the faeces and weather conditions.