Does faeces excreted by moxidectin-treated sheep impact coprophagous insects and the activity of soil microbiota in subtropical pastures?

Abstract

Abstract Moxidectin (MOX) is used to control helminth parasites in ruminant livestock being released through faeces into the environment. We aimed at evaluating the impact of MOX-contaminated sheep feces on soil coprophagous insects, microbial biomass, and activity. In a field experiment, faeces from MOX-treated rams (subcutaneous dose of 0.2 mg kg-1 body weight) and faeces from non-treated rams were placed on an animal-free pasture, protected or not from rain, for 88 days. Coprophagous insects were captured, identified, and counted, while N mineralization, and C e N contents were monitored. In a controlled experiment, faeces from non-treated animals were amended with MOX concentrations ranging from 75 to 3,000 ng MOX kg-1 faeces, mixed with soil from an animal-free pasture, and incubated for 28 days. Soil microbial biomass, respiration, and culture-microbe counting were determined. Diptera, Hymenoptera, Isoptera, and Coleoptera were equally found in faeces from both MOX-treated and non-treated animals. Faeces from MOX-treated animals had more N and degraded faster than those from non-treated animals. Even the lowest MOX concentration decreased soil microbial biomass, respiration, and N mineralization. Despite not harming coprophagous insects, the addition of MOX to feces from drug-free sheep has a negative impact on soil microbial biomass and activity.