1. Egg production, body weight, feed intake and mortality were recorded in over 78 000 broiler breeder hens in 4 commercial flocks housed in 16 houses from early lay though 40 weeks of lay. A total of 420 hens were sampled at regular intervals throughout the laying period to determine the changes in body weight and the numbers of yellow follicles, paired follicles and hierarchical positions with time in the ovary throughout lay to relate ovarian function to productivity. Average egg weight was recorded weekly from one flock.
2. A quadratic equation fitted the changes in time for the number of yellow follicles, body weight, feed intake and mortality; a linear equation described the decline in the number positions in the hierarchy and there was a linear decline in the logistic scale of the proportions of yellow follicles developing as pairs of similar weight. Egg production was described by a cubic equation and egg weight by a line plus exponential model.
3. The average number of yellow follicles declined from 7.2 to 5.4 and the number of hierarchical positions from 6 to 5 from 4 to 40 weeks after photostimulation. The proportion of follicles developing as pairs of similar weight was over 25% at the onset of lay and declined to less than 10% from 20 weeks after photostimulation, representing a substantial loss of potential productivity.
4. Body weight and egg production were similar to the breeder's targets whereas average egg weight and mortality were higher than expected.
5. The relationship defining ovarian function will facilitate the development of an improved model of egg production in broiler breeder hens.