Ractopamine Residues in Beef Cattle Hair During and After Treatment.

The objective of the present study was to assess the accumulation of ractopamine (RAC) residues in hair of Chinese Simmental beef cattle following exposure to two doses of RAC for 28 days. Six male cattle were orally administered with RAC hydrochloride at a dose of 0.67 mg/kg body weight/day (low-dose group, n = 3) and 2.01 mg/kg body weight/day (high-dose group, n = 3). The results suggested that RAC was obviously accumulated in hair, with a concentration of 5.57 ± 0.66 ng/g (white hair) and 13.67 ± 2.73 ng/g (red hair) in the low-dose group on Day 1 of treatment, respectively. In red hair, the peak concentrations of RAC were 5619.38 ± 2156.84 ng/g (low-dose group) and 6908.3 ± 1177.62 ng/g (high-dose group) on Day 14 of treatment, and then decreased slowly. In white hair, the highest concentrations of RAC were 3387.38 ± 1620.87 ng/g (low-dose group) on Day 14 of withdraw and 9621.72 ± 1497.65 ng/g (high-dose group) on Day 28 of treatment. The concentration of RAC in old hair was higher than that in new hair. No significant differences in RAC concentrations were obtained among dosage, hair color and old versus new hair (P > 0.05). The results indicated that ractopamine is significantly accumulated in red and white hair of Chinese Simmental beef cattle, which can be used as a matrix to assess the presence of RAC residues.