Faecal excretion of moxidectin in lambs and its persistence in different environmental conditions

Abstract The faecal excretion profile of moxidectin (MOX) was evaluated in Suffolk lambs (n = 7) with mean body weight (BW) of 36.06 ± 3.23, using a completely randomized experimental design. The animals received a single subcutaneous dose of 0.2 mg/kg BW. Faecal samples were collected 6, 12, 18, 24, 30 and 36 h (h), and 5, 9, 14, 21, 28, 35 and 42 days after the application of MOX. The samples were analyzed by liquid chromatography tandem mass spectrometry (LC–MS/MS QqQ). The method was validated showing 85.4–111.8% recovery and intra-day and inter-days precision values between 6.2 and 9.4%. The method limit of quantitation (LOQ) was 5.0 ng/g. The MOX showed a large excretion through the lamb faeces, with a maximum concentration (Cmax) of 22.73 ng/g at a time (Tmax) of 39.92 h. The area under the curve (AUC) value was 13,292 ng h/g. Subsequently, the persistence of MOX residues in the faeces exposed to the environment was assessed using a randomized complete block design. For this purpose, thirteen Suffolk and Dorper rams, with BW of 76.43 ± 34.24 kg, were separated into two groups: control and MOX treated. Their faeces were collected in bags at Tmax after MOX application of a subcutaneous single dose of 0.2 mg/kg BW, and were exposed to the environment. At 88th day, the MOX concentrations in the dry faeces were 29.22 ± 5.31 ng/g and 28.07 ± 5.90 ng/g whereas the initial mean concentrations were 35.94 ± 2.96 and 38.49 ± 4.71 ng/g dry faeces, with or without protection against rain, respectively. Thus, the use of rain cover to protect the faeces during exposure to the environment did not affect the residual MOX concentration in the dung. However, since the loss of faecal dry matter was higher from the faeces without cover the migration of MOX to the environment was also higher from the faeces when exposed to the environment without cover (27.08%) than with cover (18.69%). The large excretion of MOX and its sorption by the faeces and high persistence in the environment indicate that risk management actions should be taken by all the stakeholders (veterinary drug industry, farmers and government) to minimize the environmental impact of MOX on the soil fauna population in sheep production systems.