ÜBER DEN EXTREMEN GESCHLECHTS-DIMORPHISMUS IM WACHSTUM DER MOSCHUSENTE, CAIRINA MOSCHATA FLEMM.

Abstract

ABSTRACT The growth of the long bones and the development of the epiphyseal cartilage were studied in 50 male and 33 female Muscovy ducks from the time of hatching up to the 18th week. An average body weight was measured of 1990 ± 18 g in the females and of 2838 ± 99 g in the males after 10 weeks. No further increase in the body weight was noted in the females. The males continued to grow up to the 18th week and reached a final weight of 4101 ± 62 g. In the femur, the tibiotarsus, and the tarsusmetatarsus a sex difference occurred in the 2nd week and became significant after 4 weeks. The greatest difference was observed in the tibiotarsus which reached a length of 125.4 ± 0.7 mm in the male and 103.2 ± 1.1 mm in the female after 10 weeks. In both sexes the greatest increase of bone length was noted within the first 4 weeks. The bone growth ceased and the epiphyseal cartilage disappeared with about 8 weeks in the female and with about 10 weeks in the male. The humerus, the ulna and the radius were somewhat larger in the female than in the male after 4 weeks. Thereafter a more rapid growth was seen in the male. The greatest sex difference was observed in the humerus which measured 136.0 ± 1.6 mm in the male and 113.8 ± 0.9 mm in the female after 10 weeks. In contrast to the leg bones the greatest increase in body length occurred between the 6th and the 8th week. The bone growth ceased after 10 weeks in the female, and after 12 weeks in the male. Growing males which were treated with 35 mg stilboestrol weighed 2034 ± 90 g after 10 weeks. The long bones only grew to 85–90 % of the normal length. Birds which were allowed to survive a further 8 weeks after the treatment, attained a body weight of 3494 ± 111 g without any further increase in the length of the leg bones and only a slight increase in the length of the wing bones. The dwarfing effect of stilboestrol was not caused by a precocious disappearance of the epiphyseal cartilage. An identical treatment with stilboestrol had in Pekin ducks no effect on body weight or on the long bones.