EFFECT OF AGE AND BODY-WEIGHT ON PLASMA-CONCENTRATIONS OF LUTEINIZING-HORMONE IN TURKEY HENS BEFORE AND AFTER PHOTOSTIMULATION

The independent effects of age and body weight (BW) on photostimulator y response in turkey breeder hens were studied by measuring changes in plasma luteinizing hormone (LH; ng/mL) before and 3 d after photostim ulation. The study was conducted with hens from two BW groups at 24-25 , 27-28, and 31-32 wk of age. There was approximately a 1-kg differenc e in BW between groups within an age. Six hens per BW and age group we re cannulated (jugular vein) and serially sampled during each of two 6 -hr periods. Samples were collected at 10-min intervals. The two sampl ing periods were the last 6 hr of the short-day photoperiod (SD) and t he same period during the third long day after photostimulation (LD). The photostimulatory response (PR) or difference between the SD and LD baseline LH concentrations was greatest in the 24-25-wk-old hens. The PR was unaffected by hen BW at any age. The baseline LH concentration during the SD photoperiod declined as hens aged. After photostimulati on, baseline LH and LH peak amplitude concentrations were higher in 24 -25-wk-old hens compared with the older ages. The number of LH peaks i ncreased after photostimulation, but there were no significant effects attributable to age or BW within an age. In conclusion, the PR was af fected by hen age but not hen BW or BW within a particular age. (C) El sevier Science Inc. 1997.