An investigation of oral moxidectin carryover to nursing lambs via milk

The purpose of this study was to investigate the concentrations of moxidectin in the plasma and milk of lactating ewes and in the plasma of their nursing lamb. Four, single lamb bearing Border Leister x Dorset ewes were administered a single oral dose of moxidectin (0.2 mg/kg). Plasma and milk samples were collected nine times within the first 72 h and at 30 and 60 d post anthelmintic administration. Samples were measured using high-performance liquid chromatography. A pharmacokinetic analysis of moxidectin was conducted on ewe plasma and resulted in a CMAX of 13.1 ng/mL at 8.2 h (TMAX). Ewe milk and lamb plasma samples were reported descriptively. Three of the four ewes on trial demonstrated quantifiable levels of moxidectin in milk at baseline sampling. Ewe milk samples reached an average peak concentration of 151.1 ng/mL 12 h post administration. Moxidectin levels were detected up to 60 d in all milk samples. Lamb plasma samples reached an average peak concentration of 2.8 ng/mL 24 h post administration to the ewe. Results from the current study demonstrate that orally administrated moxidectin is carried over into the milk and evident in the plasma of nursing lambs. Further research is needed in order to understand how moxidectin concentrations and exposure time influences the fetus and nursing lamb in regards to the development of anthelmintic resistance.