PHENOTYPIC VARIATION, TRAIT INTERRELATIONSHIPS, AND GEOMETRIC PREDICTION OF EGG WEIGHT IN JAPANESE QUAIL (COTURNIX JAPONICA)

Abstract

In this study we studied phenotypic variation and relationships between external and internal egg quality traits in a sample of eggs from Japanese quail and whether the egg weight could be predicted from non-destructive external measurements. We had 274 individual egg records and 12 egg features (egg weight, egg length, egg breadth, eggshell thickness, egg shape index, component weight, calculated egg volume, egg density). One egg was considered structurally irregular and was removed without imputation because it had a breadth larger than the length and a shape index of 114.97%. This left us with 273 eggs for inferential analysis. The average egg weight was 7.28 ± 0.84 g, with mean length 29.83 mm, breadth 23.84 mm, shell thickness 0.221 mm, and shape index 80.03%. The egg mass was 30.81% yolk, 60.65% albumen and 8.54% shell. Egg weight was correlated strongly with breadth (r = 0.942), length (r = 0.849), yolk weight (r = 0.859) and albumen weight (r = 0.899; P < 0.001), whereas shell thickness was not related to egg weight (P = 0.958). In a parsimonious geometric model L × B², egg weight was predicted as EW = 0.284 + 0.000411 (L × B²) and R² = 0.970. The excellent reliability of the cross validation (R² = 0.969, RMSE = 0.149 g and MAE = 0.099 g) was also demonstrated with the successful prediction of a 10-fold cross validation. The results show that there is a high amount of observed variation that can be summarized with simple egg dimension and can be used for non-destructive and rapid phenotyping of Japanese quail. Without age, genotype, diet or management metadata, it is difficult to interpret causality and to make group inference.