Gifujidori hens were allowed to repeat a breeding cycle in one season. In the first breeding cycle the duration of the brooding (raising chicks) stage was limited to 3 weeks, whereas in the second breeding cycle it was limited to 1 week by removing all chicks from mother hens. In the first breeding cycle, plasma prolactin (PRL) was high during the incubation period, but rapidly decreased on the day of hatching and reached minimum values about 1 week after hatching. In contrast, plasma luteinizing hormone (LH) concentrations were low during the incubation period, but after hatching they gradually increased and reached peak values immediately after removal of chicks. Concentrations of oestradiol in plasma were low in the incubation and brooding stages but increased significantly immediately after removal of chicks. In the second breeding cycle, changes in PRL and LH concentrations were similar to those observed in the first breeding cycle except that even greater increases in plasma LH and oestradiol concentrations were observed one week after hatching when the chicks were removed. These results suggest that coexistence of newly hatched chicks may suppress LH secretion from the pituitary of the hen in the natural breeding cycle.

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Crowing of Red, Grey, Green and Ceylon Jungle Fowls, 16 breeds of Japanese native chickens and White Leghorn breed was recorded on tape and analyzed by a sound spectrography for the level of pitch, the length of duration and the number of syllable. The pitch was the highest in Grey and Ceylon Jungle Fowls and the lowest in Koeyoshi. Red and Green Jungle Fowls and Chabo had a relatively hight pitch. Duration was the longest in Totenko and longer in Tomaru and Koeyoshi. The number of syllable was 3 to 5 in the Jungle Fowls, 2 to 4 in the breeds of the Japanese native chickens, and 4 in White Leghorn breed.

These results suggest the presence of a VIP receptor in the hen hypothalamus.

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