Relationship of Production Traits and Egg Composition to Feed Consumption and the Genetic Variability of Efficiency in Laying Hens

Abstract

Abstract Influences of egg mass and egg composition traits, in addition to body weight, body weight change, age at first egg, feather cover, and sire on feed consumption between the 21st and 40th week of age were analyzed from records of 303 brown egg layers. In the basic linear model, feathering class and sire were taken as classifications and body weight, body weight change, and age at first egg as covariates. Six sets of further covariates were added to attain the complete models: total egg mass; energy in soft egg mass; yolk and albumen mass; energy and protein in soft egg mass; energy and percent shell; and yolk mass, albumen mass, and percent shell. Eighty-four percent of the variation in feed consumption could be explained by the models. Average partial regression coefficients in kilograms of feed were as follows: 3.20 for body weight (kg) at 30 weeks, 2.65 for body weight change (kg), —.20 for age at first egg (days), .68 for egg mass (kg), .12 for energy in soft egg mass (MJ 1 ), 1.80 for yolk (kg), .40 for albumen (kg), and —.25 for percent shell. A calculated reduction in yolk percentage from 28 to 23% would improve the efficiency slightly from 2.26 to 2.19 units feed per unit egg mass, respectively. The difference in feed consumption between the best and the worst feathering class was small (.4 kg). Heritability of the residual feed consumption was .50 ± .22 depending on the model. The difference between the average of the two offspring groups with the largest positive and the average of the two groups with the largest negative residual feed consumption was 1.6 kg and gave efficiency coefficients of 2.37 and 2.15, respectively. The genetic standard deviation of .52 kg and the high heritability suggest that selection for this trait could improve the efficiency of egg production.