Abstract
Studies were conducted to evaluate growth-promoting effects of testosterone in male turkeys by using castration and testosterone repletion. In three experiments, factorial arrangements with two main effects, testosterone implants and gonadal status, were incorporated, and body weights, shank length, feed consumption, and serum testosterone concentrations were measured until 20 weeks of age. Testosterone was implanted as cholesterol-based pellets at ages of 9 weeks (15.0mg/kg body weight), 13 weeks (15.6mg/kg body weight), or 11 weeks (10.1 and 20.0mg/kg body weight) in Experiments 1, 2, and 3, respectively. Castration was performed about 10 days before implants were placed. The release of testosterone from the pellet into blood circulation was immediate with a half life of 2.8 days. When implanted at 9 weeks of age (Experiment 1), the rate of weight gain was increased (P≤0.05) by testosterone, during the period of 9 to 12 weeks and decreased (P≤0.05) by castration during the period of 16 to 20 weeks. When implanted at 13 weeks of age (Experiment 2), the rate of weight gain during the period of 13 to 16 weeks was increased (P≤0.05) by testosterone. When testosterone was given at graded doses (Experiment 3), the rate of weight gain was increased quadratically (P≤0.05) by testosterone during the first 3-week period and decreased (P≤0.05) by castration during the period of 16 to 20 weeks. The overall rate of wieght gain, from 11 to 20 weeks, was increased quadratically (P≤0.05) by testosterone and decreased (P≤0.05) by castration. The feed: gain ratio was improved (P≤0.05) by testosterone treatment for the first three weeks, but not for the entire experimental period.
