Inhibition of growth in chickens by testosterone, 5 alpha-dihydrotestosterone, and 19-nortestosterone.

The growth response of poultry to androgens is ambiguous, with both increases and decreases being reported. This may reflect the use of pharmacological doses. The present study examined the effect of physiological concentrations of androgens on growth of intact male, intact female, and castrated chickens. Physiological concentrations of androgen were attained by subcutaneous silastic implants. In mammals, androgens have both androgenic effects on the reproductive organs and anabolic growth-promoting effects on body and muscle growth. Some androgens, for instance 5 alpha-dihydrotestosterone (5 alpha-DHT) have high androgenic activity (5 alpha-DHT greater than testosterone) but others, e.g., 19-nortestosterone, have high anabolic activities (19-nortestosterone greater than testosterone greater than 5 alpha-DHT). The relative effects of testosterone, 5 alpha-DHT, and 19-nortestosterone on growth were compared in chickens. In young, intact male and female chicks, growth was suppressed by 1.0-cm silastic implants of testosterone and 5 alpha-DHT (5 alpha-DHT greater than testosterone). Castrated chicks were implanted with implants of various sizes (.3, 1.0, and 3.0 cm) containing testosterone, 5 alpha-DHT, or 19-nortestosterone. The androgens inhibited body weight gain: 19-nortestosterone reducing body weight at all three doses, 5 alpha-DHT reducing body weight at the intermediate and high doses, and testosterone tending to reduce body weight only at the high dose. Testosterone (3.0 cm), 5 alpha-DHT (all doses), and 19-nortestosterone (all doses) reduces skeletal growth, as indicated by shank-toe length. In contrast to their growth-suppressing effect, all three steroids exerted an androgenic effect; stimulating comb and wattle development (19-nortestosterone greater than 5 alpha-DHT greater than testosterone). It is concluded that androgens are androgenic but are not anabolic in chickens.