Selection for high and low percentages of chicken eggs with blood spots 1

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Abstract
Eggs were examined for presence of blood spots in a base generation of White Leghorns part of which were fed on an adequate diet and part on a diet inadequate in vitamin A that increased blood spot incidence. From theory and data, the selection differential was larger for low incidence selection for pullets on the inadequate diet than pullets on the adequate diet. Statistical and genetical models were given for estimating variances of this all‐or‐none trait with h 2 = 0.16 and 0.60 for the lines on the adequate and inadequate diets respectively. Predicted selection gains for individual selection of females alone were: adequate diet, low ‐0.91%, high 2.36%; inadequate diet, low ‐10.71%, high 14.58%. After eight generations of selection for high and low incidence on each of the diets there was a difference of 23.5% between high and low lines selected on the adequate diet and 37.7% on the inadequate diet. Evidence was inconclusive that selection for low incidence on the inadequate diet produced birds with a lower incidence on the adequate diet than birds selected on that diet. Specific gravity showed a negative correlated selection response in both lines on the adequate diet but no correlated response was evident in the lines on the inadequate diet. There was a negative correlated response for Haugh units and a positive correlated response for blood spot size in all lines. Egg weight did not show a correlated selection response.