Mechanism of Difference in Growth Rate Between Cockerels and Pullets

IT HAS been established that cockerels show a greater and more rapid gain in body weight than do the pullets (Kempster, 1921; Carver and Hougan, 1935). Similar results are also obtained by adding some antibiotics and vitamin B12 in the feeds (Branion and Hill, 1951; Heuser and Norris, 1952). It has not been determined, however, if this difference is due only to a difference in the amount of the feeds consumed, or to difference in the absorption or utilization of the feeds after consumption. In order to determine if the latter of these two factors was important, the following experiment was carried out. METHODS AND RESULTS Twenty-four White Leghorn chicks (Chaing’s strain) averaging 36 gm. each were used. Half of them were cockerels and the others pullets. They were kept under the same conditions and there was marked difference in body weight between cockerels and pullets at the end …