A genetic analysis of egg quality traits and their maternal influence on offspring-parental regressions of juvenile body weight performance in broiler chickens

The maternal egg characteristics, length, width, weight at set (EWT), specific gravity (SG), weight at transfer (WTT) and weight loss from set to transfer (WTL) were measured for female line meat-type chickens to investigate: (1) the genetics of these egg quality characteristics and (2) the effect of these maternal traits on (bias of) the offspring-parental regressions for JBWT performance and the significance of their regressions. Animal model REML heritability estimates of the egg traits had intermediate to high values, ranging from 28% for SG to 55% for WTT. Simple regression coefficients of offspring on sire and dam for JBWT were significantly different (0.20 and 0.26, respectively). Extension of this straightforward regression model with covariates on all the maternal egg quality phenotypes as well as a second variance component due to common permanent environment of full siblings alleviated the asymmetry in offspring-sire and offspring-dam regressions (0.23 and 0.24, respectively). EWT and WTT had significant antagonistic partial effects on the dam regression (−0.06 and 0.07, respectively). The antagonistic effects of these maternal pathways largely offset each other, and hence biased the offspring-dam regression only slightly (0.01). The scope for application of these types of models, assuming observed maternal performances, in animal breeding to improve the progress in traits of direct and maternal importance was discussed.