Research note: Comparative estimation of genetic parameters for eggshell pigmentation traits

Eggshell color exhibits considerable variation, with the diversity particularly rich in shells where protoporphyrin serves as the primary pigment. The measurement of eggshell color typically employs the Commission International del'Eclairage (CIE) L*a*b* color space system, which precisely describes color based on three dimensions: lightness (L*), red-green (a*), and yellow-blue (b*). However, in comparative studies of different egg colors, the lightness value (L*) is most frequently utilized, while the use of a*and b*values remains relatively insufficient. To comprehensively evaluate eggshell color, several comprehensive color indices, including quantities of true protoporphyrin IX (Q_p), Shell Color Index (SCI), Chroma (C*), and Hue Angle (h°), have been proposed. Nevertheless, it remains uncertain which index more suitable evaluates the eggshell color. This study involved 1,481 Rhode Island Red chickens and 1,938 Dwarf chicken. Eggshell color data were collected at 43, 60, and 80 weeks of age, and genetic parameter estimates were made for each comprehensive egg color index. The results indicated that, in terms of phenotypic correlation with L*, Q_p was superior to SCI, followed by h°, and finally C*. The Q_p value decreased with increasing age, validating the observed trend of eggshell color becoming lighter as hens age. Estimates of genetic parameters revealed that the heritability of Q_p ranged between 0.37 and 0.42, indicating a moderate to high level of heritability. The heritability of SCI ranged from 0.32 to 0.44, that of C* ranged from 0.23 to 0.41, and that of h° was 0.46. All comprehensive color indices showed medium to high heritability. In conclusion, Qp and SCI more accurately reflects variations in eggshell color. Therefore, it is recommended that Qp and SCI be adopted as the phenotypic parameter for eggshell color in breeding programs for brown- and pink-shelled laying hens to facilitate accelerated genetic progress.