Egg Morphology as a Phenotypic Indicator of Chick Sex and Early Growth in Thai Native Chickens

Egg morphological characteristics have been associated with hatchability, chick quality, and sex-related variation; however, their relationships with juvenile growth in indigenous chickens remain unclear. This study evaluated associations among egg morphology, hatch weight, chick sex, and early growth in Thai native Pradu Hang Dum chickens. A total of 139 chicks were evaluated for egg length, egg width, egg weight, eggshell surface area, shape index, hatch weight, body weight, and chest circumference. Pearson correlation, multiple linear regression, logistic regression, receiver operating characteristic analysis, and exploratory path analysis were applied. Egg length was positively associated with body weight and chest circumference at 8 weeks, whereas shape index was negatively associated with both traits. Egg weight was strongly correlated with hatch weight (r = 0.721, p < 0.001). After adjustment for chick sex, egg weight and shape index were not independently associated with body weight at 8 weeks, whereas sex showed a strong association; the model explained 41.0% of the observed variation. For chest circumference, shape index and sex remained significant, and the model explained 18.0% of the variation. Logistic regression showed significant associations between egg morphometric traits and chick sex, with similar within-sample discrimination for shape index alone (AUC = 0.808) and the model combining egg length and width (AUC = 0.814). Exploratory path analysis showed significant paths from egg weight to hatch weight, hatch weight to 8-week body weight, sex to 8-week body weight, and 8-week body weight to chest circumference. Overall, egg morphology provided population-specific phenotypic information associated with chick sex and early development, but its independent value for explaining juvenile growth was limited after accounting for sexual dimorphism.