Concentration of 17α-Methyltestosterone in HormoneTreated Feed: Effects of Analytical Technique, Fabrication, and Storage Temperature

Feed treated with 17α-methyltestosterone (MT) is used to manipulate the gender of early tilapia fry. In the USA, hormone-treated feed is used by selected producers under an Investigational New Animal Drug (INAD) program. While monitoring the fabrication and on-farm use of this treated feed, concerns were raised about the high performance liquid chromatography (HPLC) analytical procedure for detecting MT in feeds, the incorporation of MT in feeds during fabrication, and effects of storage temperature on MT concentration. A series of experiments demonstrated that the analytical procedure for detecting MT in feeds lacked high precision, and, on average, biased results low. MT was uniformly mixed with feed by spraying an MT-alcohol solution on feed while it was blended in an industrial ribbon mixer. Alcohol volumes ranging from 15 mL/kg to 150 mL/kg were equally effective at dispersing MT in feed. The concentrations of MT in feeds consistently declined over time if the storage temperatures were 25 C or higher. Freezing preserved the MT in feed, and the refrigeration of feed fabricated to contain 60 mg MT/kg maintained acceptable MT concentrations during 6 mo of storage.