Genetic basis of the increase in egg weight with pullet age in a White Leghorn flock.

1. In a closed White Leghorn flock over a 6-year period the average increase in egg weight from the start of lay to 37 weeks of age was 12.6 g. 2. The heritability of this egg weight increase was estimated at 0.36 +/- 0.06. 3. The genetic correlations of egg weight increase with other characteristics were: age at first egg -0.50, early egg weight -0.51, 37 week egg weight 0.42 and egg production to 273 d 0.44. 4. It is predicted that with unit selection intensity the direct response in egg weight increase will be -1.30 g, with correlated responses in age at first egg of 2.1 d, early egg weight 0.64 g, 37 week egg weight -0.51 g and egg production to 273 d -1.83 eggs.