Preovulatory luteinizing hormone surge interval in old and young laying turkey hens early in the egg production period

Egg production rate normally declines with duration of the reproductive per iod, but hen age and duration of the reproductive period are usually confou nded. Initiation of egg production can be delayed in turkey hens with short -day lighting, allowing hen age to be separated from duration of the reprod uctive period. The objective of the present report is to determine if the i nterval between luteinizing hormone (LH) surges is different between old an d young laying turkey hens during the peak of egg production. Turkey hens w ere given short-day lighting [6 h light (L):18 h darkness (D)] at 16 wk of age, and were photostimulated with 24L:OD (constant light) at 30 (young hen s) or at 70 (old hens) wk of age. Egg production in the young hens started about 2 wk after they were photostimulated, but some of the old hens had st arted laying at 64 wk of age while under short-day lighting, and all old he ns were laying after 1 wk of photostimulation. To monitor the interval betw een plasma LH surges at peak of production, hens were serially bled hourly for 240 h, starting about 6 wk after photostimulation. The interval of LH s urges was not different between young (n = 5) and old (n = 10) laying hens. Not all LH surges were coincident with oviposition of eggs 1 to 2 d later (blind LH surges), and the percentage of young hens with at least one blind LH surge was higher than for old hens (60% of young hens and 10% of old he ns). The baseline concentration of LH was not different between the young a nd old laying hens. In conclusion, the interval between LH surges, baseline concentration of LH, and amplitude of LH surges were not related to age of the hens during the peak rate of lay.