Residue content of beef feedlot manure after feeding diethylstilbestrol, chlortetracycline and ronnel and the use of stirofos to reduce population of fly larvae in feedlot manure

Two beef cattle feedlot experiments were conducted to determine the amount of certain agricultural chemicals that are likely to be found in both fresh and stored feedlot manure and to investigate fly control in this manure. In experiment 1, diethylstilbestrol (DES), chlortetracycline (CTC), and ronnel were used as feed additives. Fresh manure, stored manure, runoff water, manure weathered on pasture, and soil from pasture fertilized with manure were analyzed for these additives. Stirofos was added to fresh manure as a larvicide for fly control. In experiment 2, the residue aspects of DES and CTC were repeated. In this experiment, stirofos instead of ronnel was fed with DES and CTC. Sixty-eight percent of the DES fed to cattle appeared in fresh manure and 52% in manure stored for 12 weeks. Comparable percentage values were 17 and 11% for CTC and 13 and 3% for ronnel; somewhat less DES and CTC were found when a concentrate diet was fed. Detectable amounts of DES, ACT, and ronnel were not found in runoff water, weathered manure, or soil. Adding an emulsifiable concentrate formulation of stirofos directly to manure at a rate of approximately 45 ppm of wet manure completely controlled the larvae of house fly (Musca domestica L.) whereas feeding stirofos at a rate of 1.5 mg per kg of body weight daily reduced larval counts 82% in manure from forage-fed heifers and 63% in manure from concentrate-fed heifers. Stirofos was not detected in runoff water, weathered waste, or soil.