Studies of the transformations of substituted urea herbicides in rumen fluid, using metobromuron as a pilot compound, indicated that one of the products is the corresponding aniline. Because it was possible for a diazotization reaction to take place from the reduction of nitrate to hydroxylamine and ammonia through a transient nitrite step, the formation of azo compounds in rumen fluid was investigated. Incubation of 3,4-dichloroaniline with rumen fluid did not result in t he formation of any measurable azo compounds. The stability in rumen fluid of a known azo compound, 3,3’,4,4’-tetrachloroazobenzene, was also studied. Evidence is presented to show that azo compounds can break down in rumen fluid.

Oxytetracycline was fed continuously to broilers at 25 to 200 g/ton from the age of 1 day to 11 weeks. Residues in the muscle tissue at 11 weeks ranged from trace quantities at 25 g/ton to 0.20 μg/g at 200 g/ton; liver residues ranged from not detectable to 0.29 μg/g at 200 g/ton; kidney levels ranged from 0.09 to 0.78 μg/g at 200 g/ton. Tissue, blood, liver, kidney, and intestinal contents were negative 24 hr after withdrawal from the drug. Cooking destroyed all residues in muscle tissue but livers retained 50% of the uncooked levels. Eggs from hens fed up to 400 g/ton contained no measurable residues.

Chlortetracycline was fed continuously to laying hens at levels of 0, 50, 100, 150, and 200 g/ton for a period of 4 months. Eggs from hens on the hasal ration showed a miniscule rate of positives, 2.1%; eggs from hens fed 50, 100, and 150 g/ton showed a positive presumptive rate of 58.3, 11.8, and 3.5% and a measurable residue rate of 11.1, 83.8, and 94.9%; and eggs from hens fed 200 g/ton had a 100% measurable rate. Preparation of eggs by several cooking procedures indicated a 30–50% retention of potency.

The feeding of penicillin to broilers and laying hens did not result in the deposition of any penicillin activity in the blood, muscle, liver, kidneys, or eggs. About 9 8% of the penicillin activity was destroyed in the upper portion of the intestinal tract with very little activity reaching the small intestine. When penicilloic acid, one of the degradation products, was fed to broilers it stimulated the development of lactosefermenting organisms in the intestinal tract, which showed antibiotic resistance as reflected by the streptomycin and tetracycline resistance markers.

The microbiological assay for penicillin residues was improved by using centrifugation to remove physical barriers to diffusion, a small buffer/meat extraction ratio, and a more sensitive 2-layer assay system. Recoveries from muscle, kidney, and liver tissues ranged between 70.1 and 86.7% with measurable levels of 0.03- 0.05 unit/g. By comparison, the Food and Drugsuggested methodology yielded recoveries of 45.9-54.0% and levels of detectability of 0.08- 0.10 unit/g. Cooking of hamburger, steaks, and pork chops indicated that procaine penicillin withstood cooking conditions, and significant levels of the original activity remained.