Comparative depletion of sulfamethazine in bob veal, fancy veal, and replacement calves

The Code of Federal Regulations provides for the use of sulfamethazine (SM) boluses in cattle, a tolerance of 0.1 ppm for SM in meat, and a 10-day withdrawal. Bob veal, fancy veal, and replacement calves were dosed with SM as provided in the regulations and the rate of depletion of SM and, where practicable, N4-acetylsulfamethazine and desaminosulfamethazine were measured in liver, kidney, and diaphragm muscle by gas chromatography. SM concentrations reached lower maximum levels and depleted faster in the tissues of replacement calves than in bob veal and fancy veal calves. Average SM levels on d 5 of withdrawal in liver, kidney, and diaphragm were about 1 ppm in fancy veal, above 2 ppm in bob veal, and below 0.1 ppm in replacement veal. Two of the d 14 and two of the d 10 withdrawal fancy veal livers contained more than 0.10 ppm of SM. A 10-d withdrawal period may not be long enough for bob and fancy veal calves that have been dosed according to the drug label.