Changes in ovarian function and egg production in commercial broiler breeders through 40 weeks of lay.

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.

Successful modification of a stochastic model of egg production in broiler breeders housed in temperate climates to predict flock productivity in tropical farms in Venezuela.

1. The production of hatching eggs in tropical flocks of broiler breeders was estimated from records of initial body weight and subsequent body weight gains from 6 flocks containing over 140,000 birds in Venezuela using a stochastic model developed in temperate climates. The model was then modified to account for the greater persistency of egg production in the tropical environment of Venezuela. 2. The tropical model overestimated total egg production by 1.8 eggs. Lin's concordance correlation coefficient averaged 0.99 compared with 0.85 for the temperate model of egg production. 3. It was concluded that the modified model simulated egg production sufficiently well in the tropical environment to make it a useful management tool. Breeding company recommended target rates of lay for broiler breeders subjected to a long photoperiod during rearing such as in the tropics should be modified to account for their greater persistency of lay.

Similar improvements in reproductive performance of male line, female line and parent stock broiler breeders genetically selected in the UK or in South America.

1. Field data on the reproductive performance of parent stock and grandparent female line and male line broiler breeders were extracted from a commercial database covering the years of hatch from 1989 to 2002. The data were from the UK, Western Europe, Central and South America and Japan. Quadratic regression curves were fitted to the data to estimate the long-term phenotypic trends in total egg production, hatching egg production, chick numbers, hatchability and female mortality. 2. Changes in performance over time were similar in the UK, Western Europe and Central and South America and are consistent with the suggestion that genetic selection in separate breeding programmes in the UK (supplying the UK and Western Europe) and Brazil (serving Central and South America) was associated with similar improvements in the performance of commercial parent stock and grandparent flocks. Changes in performance in Japan (supplied from the UK) were different but recent performance was similar to those in the other regions. 3. The mean annual improvements over 10 years to 2002 for male line, female line and parent stock, respectively, were 0.4, 1.7 and 1.7 for total egg number; 0.5, 1.8 and 1.6 for hatching egg number; 0.6, 1.8 and 1.3 for total chick production; 0.25, 0.47 and 0.09% for hatchability; and -0.69, -0.05 and -0.41% for female mortality. 4. The results are consistent with claims that significant genetic change in pedigree selection (nucleus) flocks by the primary breeding company are reflected in substantial improvements in reproductive performance in commercial flocks. The presence of similar rates of improvement in different geographical regions as a result of genetic selection in two continents representing tropical and temperate regions suggests that genotype-environment interactions for reproduction traits are not important.