The endocrine control of egg production in poultry

• Main Author: Williams, John B.
• Published: University of Edinburgh 1978
• Subjects: 636
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663821

Experiments were conducted to determine the importance of progesterone in egg production. Plasma levels of progesterone were found to be higher in laying birds than in immature or non-laying females. In the laying hen, progesterone is produced chiefly by the mature ovarian follicle before it ovulates, and this triggers the pre-ovulatory discharge of luteinizing hormone (LH). Egg production was observed to decline in the first twelve months of lay in three strains of hen examined (2 egg-producing strains; 1 broiler breeder strain) and this decline is partly due to birds laying shorter sequences of eggs, but the range of times in which egg-laying normally occurs each day did not vary with the age of the hen. The onset of lay was concomitant with an increase in progesterone secretion, but the rates of lay of the 3 different strains in the first year of egg production was not correlated with progesterone secretion. However, a direct correlation with basal plasma LH levels was observed. Neither the sensitivity of the pituitary to LH-RH nor the sensitivity of the ovary to ovine LH was different in young, high producing hens or old, lower producing hens but a decline in the sensitivity of the CNS mechanism regulating the pre-ovulatory release of LH was noted in older hens. The follicular structure of the ovary was not different in high and low ovulating strains of hen, but age-related changes were observed. Older birds tended to have fewer follicles developing at a time, and this was thought to be one reason why egg production declines with age. Hens laying at very low rates had essentially normal ovaries and it was the failure of many follicles to reach the outside world in fully-formed eggs which was an important cause of low production in these hens.