Genetic parameters of egg quality traits on different pedigree layers with special focus on dynamic stiffness

Egg quality traits are of utmost importance in layer breeding programs due to their effect on profitability in the egg production industry and on the production of quality chicks. Therefore, the aim of this study was to analyze and estimate genetic parameters of different quality traits: egg weight, breaking strength, dynamic stiffness (K-dyn), egg shape index, eggshell thickness, and albumen height. Eggs were obtained from 4 pure lines of birds. Two different tests were performed: a white breeding program, with eggs from a male and female line of a white egg layer program that were analyzed at 67 to 70 wk of age, and a brown breeding program, with eggs from a male and female line of a brown egg layer program that were analyzed at 32 to 36 wk of age. In general, heritabilities were moderate to high for all traits (h(2) = 0.23 to 0.71). A high genetic correlation was estimated in both tests between breaking strength and K-dyn (r(g) = +0.40 to +0.61). Shell thickness was also positively correlated with breaking strength (r(g) = +0.50 to +0.63) and K-dyn (r(g) = +0.28 to +0.69). These moderate relationships demonstrate that the strength of an egg not only relies on the shell thickness but also on the quality and uniformity of eggshell construction. Dynamic stiffness might be preferred for breeding purposes due to its lower negative genetic correlation with egg weight and its higher heritability (h(2) = 0.35 to 0.70) compared with breaking strength (h(2) = 0.23 to 0.35). Breaking strength and K-dyn were positively correlated with shape index, which confirms that round eggs will show higher shell stability. Therefore, it is necessary to monitor egg shape to maintain an optimal form.