Effects of age and of early lighting on ovarian function in breeding turkeys

1. Yellow follicle numbers and production of defective egg shells were greater in the early part of the laying period in conventionally-reared turkeys photostimulated at 24 rather than 30 weeks of age. 2. The number of yellow follicles declined with age and were similar in both groups at 40 weeks of age. 3. At 55 weeks of age more birds photostimulated at 24 weeks were out of lay and birds in lay had fewer yellow follicles and more atresia compared with turkeys photostimulated at 30 weeks of age. 4. The numbers of white follicles in the 1 to less than 2 mm size were similar in the two groups at each age. The proportion of white follicles which were atretic was negatively related to the number of yellow follicles, particularly in follicles 5 to less than 8 mm diameter.