Residue depletion studies were conducted in dairy cattle to monitor
morantel-related residues in milk following
oral administration of
morantel tartrate (Rumate. Eleven lactating cows of various ages, periods of lactation, and known milk production were orally dosed with the bolus formulation of
morantel tartrate with an actual dose range of 8.4-9.8 mg/kg
body weight. Representative samples of milk were collected
at 10-14 h intervals post-dose, and subsamples were assayed for the major and minor hydrolysis products of
morantel-related residues, MAPA and CP-20,107. Residues assayed as precursors of MAPA peaked at the second milking (24 h post-dose) and were below 25 ppb (range: less than 12-24 ppb). Precursors of CP-20,107, which confirm the identity of
morantel, also peaked at 24 h post-dose (range: 2.1-3.3 ppb) and declined rapidly thereafter. A statistical model was used to project the level of residues at the upper limit of 99% of the total target animal (i.e., dairy cattle) population with 95% confidence. The calculated peak levels from this model were 50 and 5.0 ppb for
morantel-related residues convertible to MAPA and CP-20,107, respectively.