Food consumption records for the genetic improvement of income over food costs in laying flocks of white leghorns

1. A study of genetic parameters of egg mass based on the weights of all eggs laid, individual food consumption, body weight and age at first egg was made. Data from three populations differing in average egg weight were available over two production periods, from 20 to 40 and from 40 to 60 weeks of age, respectively.

2. Selection indexes designed to maximise income over food costs (IOFC) were used to evaluate the usefulness of food consumption data for the genetic improvement of laying flocks.

3. Given reliable estimates correlating food consumption to egg mass, body weights and age at first egg it is possible to construct highly efficient selection indexes for genetic improvement of IOFC without the direct use of food consumption data.

4. Selection for genetic gains in egg mass appears to be the most important factor for genetic improvement of IOFC. Correlated increases in egg weight were observed for two of the populations.

5. Body weights showed very small and inconsistent genetic responses under index selection suggesting that a reduction in body weight need not be necessary for more efficient egg production.

6. Indexes which showed greatest genetic improvement also resulted in an increase of food consumption. Thus genetic efficiency in egg laying flocks would be achieved by increasing egg mass through earlier sexual maturity, larger eggs and higher production rates with increased food consumption and only slight, if any, reduction in body size.

7. Estimates of heritabilities and genetic correlations indicate that food consumption measurements can be based on partial records; high heritabilities were found for egg mass and food consumption measurements in both early (20 to 40 weeks) as well as late (40 to 60 weeks) production periods.