[Detection of the critical period of pituitary-adrenal system development during postembryonic chicken ontogenesis]

Studies have been made on postembryonic development of the hypophyseal-adrenal system in domestic hens. Most significant functional rearrangements were observed at the 3rd week of life, when corticosteroid content of the blood plasma decreased threefold. Birds subjected to a series of cold stresses at this time, exhibited more rapid sexual maturation, more rapid reaction of the adrenals to exogenous corticotropin and higher resistance to unfavourable factors. Stress expositions in other days of the first month of life also resulted in trace phenomena, although these were less evident. It is suggested that the 3rd week after hatching is a critical period in the development of ihe hypophyseal-adrenal system in hens.