Why is a slow, gradual increase in photoperiod during lay essential to sustain high lay persistency beyond 80 weeks of age?

The reproductive cycle of a laying hen is controlled by light. Light rays penetrate the thin skull of the chicken, stimulating photoreceptors in the hypothalamus to secrete Gonadotropin-Releasing Hormone (GnRH). GnRH acts on the pituitary gland to release Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), which drive ovarian follicle development. When pullets start laying, farmers increase the photoperiod from 12 hours to 16 hours. However, if this light increase is done too rapidly (e.g., jumping from 12 to 16 hours in a single week), it over-stimulates the hypothalamus. This triggers a massive, sudden spike in egg production, but it rapidly exhausts the pituitary gland's hormonal reserves, leading to an early "flock burn-out" where egg production drops sharply after 45 weeks of age. To achieve an elite lay persistency (maintaining over 80% lay up to 80 weeks), the photoperiod must be increased slowly and gradually—by exactly 15 to 30 minutes weekly—until reaching the maximum 16 hours. This slow stimulation maintains a balanced, continuous secretion of FSH and LH, ensuring stable egg numbers and superior shell quality over the entire lifetime. Farmers can read photoperiod kinetics in the Poultry Encyclopedia, buy automated programmable lighting dimmers on Poultry Plaza, track daily egg rates on Poultry Rates, and list persistent flocks on Murghi Mandi.