Sensitivity to testosterone varies with strain, sex, and site of action in chickens

Abstract

Day-old chicks (cockerels and pullets) of two strains of chicken (a commercial breed and strain of feral fowl) were treated intramuscularly with 25 mg/0.1 ml of testosterone oenanthate on day 1 posthatching. Controls received 0.1 ml of the vehicle. Attack and copulatory behavior were scored from days 7 to 14 using standard hand-thrust tests, which rank the responses from 1 to 10. The sizes of the comb and testes were also measured. All measures showed strain and sex differences. Copulation and attack scores were highest in males of the feral strain. Even untreated males of the feral strain had high scores, and these were further elevated by the testosterone treatment. In fact, the attack scores of feral males were marginally higher than those of the males of the commercial strain treated with testosterone. Testosterone treatment of the feral females also elevated attack and copulation to a much greater extent than in the commercial strain. Opposite effects occurred for the development of the comb. Comb volume, absolute and adjusted for body weight, was much greater in treated chicks of the commercial strain than in those of the feral strain. These results indicate that chicks of the feral strain may have more central and fewer peripheral receptors for testosterone or that their receptors for testosterone are more sensitive than those of the commercial strain. Alternatively, there may be strain, as well as sex, differences in the metabolism of testosterone.