Effect of hen age, body weight, and age at photostimulation. 1. Egg, incubation, and poult characteristics of commercial turkeys.

Turkeys from two BW groups (which averaged 11.8 and 12.9 kg, Normal and Heavy, respectively) were photostimulated at either 29 or 31 wk of age to determine what effects age-associated changes in hen carcass characteristics, egg weight, and egg components have on subsequent poult weight at hatching during the first 10 wk of production. Carcass measurements were determined from a subsample of hens 3 wk after photostimulation (PS). Subsamples of eggs from each PS age and BW group were selected for yolk and albumen measurements. All other eggs from these hens were individually weighed and incubated at 2-wk intervals during the first 10 wk of lay (4 to 14 wk after PS). All incubated eggs were reweighed at 25 d (transfer) and poults were individually weighed at hatch. Hen BW at PS had no effect on ovarian weight and follicular size or number 3 wk later. Hens photostimulated at 31 wk had 18.7 g heavier ovaries 3 wk after PS than hens photostimulated at 29 wk (P < or = 0.06), primarily due to one additional follicle of > or = 20 mm (P < or = 0.04). During the first 10 wk of lay, egg weight increased 7.8 g, 4.4 g of which was due to increased yolk weight. Eggs from Normal BW hens weighed significantly less than those from Heavy BW hens only when hens were subjected to PS at 29 wk. Egg weight at transfer relative to egg weight at set was significantly increased from hens 4 to 6 wk after PS compared with the four older production ages (6 to 8, 8 to 10, 10 to 12, and 12 to 14 wk after PS). There was a significant increase in poult weight with increasing hen production age but no changes in poult weight relative to egg weight at set. In conclusion, hen BW at PS had minimal effects on egg component weights and subsequent poult weight at hatching.