Neuroendocrine Control of Reproduction in the Cockerel

INTRODUCTION Testicular activity in the cockerel is controlled by the brain. Information from the external environment, such as changes in daylength, housing conditions, or social status, and from the internal environment, relating to such factors as nutritional status, somatic maturity, or general bodily health, is integrated in the brain to modulate the secretion of gonadotrophin releasing hormone (GnRH). Only small amounts of GnRH are released from the brain and they function as neuroendocrine signals which are amplified by the pituitary gland. Thus, relatively large amounts of luteinizing hormone (LH) and follicle stimulating hormone (FSH) are released from the pituitary gland in response to a small release of GnRH. The levels of LH and FSH in the peripheral circulation are directly related to testicular activity and to the production of spermatozoa. Avian GnRH is chemically similar but not identical to mammalian luteinizing hormone releasing hormone (LHRH) (King and Millar, 1979). Mammalian …