CHANGES IN PLASMA LUTEINIZING-HORMONE CONCENTRATION IN TURKEY HENS AFTER SWITCHING FROM SHORT-DAY TO LONG-DAY PHOTOPERIODS

Luteinizing hormone (LH) has been reported to increase in plasma short ly after switching photosensitive turkey hens from shea-day (SD) photo periods (6 hr light:18 hr dark) to long-day (LD) photoperiods (14 hr l ight:10 hr dark). An experiment was conducted to determine the timing and nature of these changes in plasma LH concentrations after the phot ostimulation of photosensitive turkey hens. The turkey hens were cannu lated (jugular vein) to allow serial bleeding every 15 min for 48 hr. One group (controls) was continued under the SD photoperiod, and one g roup (treated) was switched to the LD photoperiod by the addition of 8 hr of light to the end of the photoperiod. In the control hens, no ch anges were seen in the observed or calculated baseline concentrations of LH or in the frequency and amplitude of LH peaks during the 48 hr o f serial bleeding. In the treated hens, the observed and baseline conc entrations of LH increased during the first LD scotoperiod, with a fur ther increase during the second LD scotoperiod. This rapid increase wa s due to an increase in the baseline LH concentration, whereas no cons istent changes were detected in the frequency and amplitude of LH peak s.