EFFECTS OF TIMING AND SIZE OF DAYLENGTH CHANGE ON BROWN EGG-LAYING DOMESTIC HENS - PLASMA LUTEINIZING-HORMONE CONCENTRATION AND SEXUAL MATURITY

1. Brown egg laying pullets were transferred from an 8-h photoperiod t o an 8-, 10-, 13- or 16-h photoperiod at 6, 9, 12, 15, 18 or 20.3 week s of age. Plasma luteinising hormone (LH) concentrations were measured at transfer and 7 and 14 d afterwards. 2. Significant increases in pl asma LH occurred following light stimulations at 6, 9 and 12 weeks of age. 3. Changes in LH concentration 7 d after a light increase from 8 h to 8, 10, 13, 16 h were highly correlated with photoperiod length at 9 and 12 weeks of age. 4. Changes in LH were generally poorly correla ted with age at sexual maturity, although the reduced influence on age at first egg of a light increase given close to sexual maturity was r eflected in minimal LH responses at 18 and 20.3 weeks.