IN AN EARLIER STUDY an attempt was made to determine the number of genes forbroodiness carried by cocks by means of hormone treatment rather than breeding tests (Nalbandov and Card 1945). It was found in that study that sufficient amounts of prolactin will cause males, regardless of their genotypes, to show most of the broody responses shownby broody hens. The amount of prolactin required to bring about this response in maleswasroughly inversely proportional to the number of genes for broodiness assumed to be carried by them. Regardless of the dosage of prolactin injected none of the males could xgbe induced to incubate eggs, but they will assume complete charge of a group of day old chicks.Tasks usually identified with the broody hen would then be executed by prolactin-treated males who would lead chicks to feed and water, protect and shelter them under body and wing, attack and drive away aggressors and utter a variety of vocal sounds, including clucking, normally not heard from males, but understood and obeyed by the chicks. Uninjected males, when confined with chicks, either kill them or allow them to die of starvation and exposure, because of active antagonism or lack of interest.
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Nalbandov et al. (1945) studied this question.