DISTRIBUTION OF RADIOCARBON AFTER INTRAMAMMARY, INTRAUTERINE, OR OCULAR TREATMENT OF LACTATING COWS WITH C-14 NITROFURAZONE

Three lactating Holstein cows (634 to 698 kg) were dosed, respectively , with 65.6 mg (44.5 mu Ci/ mg), 131.2 mg (20.1 mu Ci/mg), or 8.4 mg ( 141.3 mu Ci/ mg) of [C-14]nitrofurazone by intramammary, intrauterine, or topical ocular administration. Intramammary and intrauterine treat ments were single doses; ocular treatment was daily for 4 consecutive d (2.1 mg/d). Cows were slaughtered after 72-h withdrawal. periods. Ex creta and milk were quantitatively collected fi om each cow after dosi ng. Seventy-two hours after treatment, urine, feces, and milk containe d 62.9, 17.6, and 2.3%, respectively, of the radiocarbon administered intramammarily to the cow. Radioactive residues in milk collected from the dosed quarter were 150 ppb (nitrofurazone equivalents) and were 3 9 ppb in milk collected from the undosed quarters at 12 h after dosing . Urine, feces, and milk from the cow that received the intrauterine d ose contained 12.24, 5.17, and 0.13% of the administered dose, respect ively, at 72 h after treatment. Concentrations of total radioactive re sidues in milk were 9.3 ppb at 12 h after dosing. For the cow that was dosed ocularly, the cumulative excretion of radiocarbon in urine, fec es, and milk was 17.6, 28.5, and 0.5% of the dose, respectively. Milk residues from the cow that was dosed ocularly were never >1 ppb of nit rofurazone equivalents. Livers and kidneys contained the greatest amou nts of residues relative to other edible tissues. Parent nitrofurazone was not suitable as a marker compound to determine total residues in milk using HPLC analysis. Radioactive residues were available systemic ally and were excreted in milk after intramammary, intrauterine, or oc ular application of [C-14]nitrofurazone. Illegal residues in milk and edible tissues would result from the administration of nitrofurazone t o lactating cows.