Abstract
ABSTRACT The study aimed at investigating which of four traits is the most representative of eggshell strength (destructive eggshell thickness measurement, eggshell weight, egg specific gravity, ultrasonic measurement of eggshell thickness) and could be used for selection purposes. To date, investigations focused mostly on pairwise (eggshell strength vs. another eggshell feature) analyses, resulting in two-, maybe three-trait, models when eggshell traits are considered. Since the covariance estimates are also model dependent, we collected five eggshell traits within one analysis, which better reflects what occurs in nature. The eggs were collected from 4571 Rhode Island White and 2426 Rhode Island Red hens. A multiple-trait animal model and the REML method were employed to compute variance components for calculation of heritabilities and genetic correlations between the traits. On average, the highest correlations were found between the destructive measurement and the other quality traits. It is concluded, however, that the ultrasonic eggshell thickness measurement, also with high genetic correlations with the other traits and leaving an egg intact for further handling, can suit best, as an indirect criterion, the selection for eggshell strength.
Highlights
Eggshell is a structure of major importance in layer breeding, influencing two economically vital aspects in commercial egg production – the eggshell protects the embryo, while enabling its development, and has an impact on the level of losses in the production of consumption or hatching eggs (Mertens et al, 2006).Eggshell quality has long been subjected to genetic selection, and considerable improvement of eggshell quality has been reported (Hocking et al, 2003)
The genetic correlation between DET and UET was very high in both breeds, of 0.82 and 0.95 in Rhode Island White (RIW) and Rhode Island Red (RIR), respectively
The usefulness of a trait for genetic selection is determined by the genetic additive effects reflected by a sufficiently high heritability coefficient
Summary
Eggshell quality has long been subjected to genetic selection, and considerable improvement of eggshell quality has been reported (Hocking et al, 2003). Some main features of the eggshell are its strength expressed as the force needed to crack it, thickness, and weight. Before the emergence of non-destructive measurement devices (Kibala et al, 2015), destructive methods, leaving the egg unsuitable for further handling, were employed to evaluate eggshell quality. In order to avoid egg destruction, other traits genetically correlated with the eggshell strength, such as the ultrasonic measurement of eggshell thickness (ibid) and egg specific gravity (Rozempolska-Rucinska et al, 2011), were proposed as indicative of eggshell strength. Any of the above egg traits may be employed as criterion for the selection for eggshell strength; only ultrasonic eggshell thickness measurement and egg specific gravity leaves the egg intact
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