Estimation of genetic parameters for traits related to external and internal egg quality in wild and white Japanese quails

Quails are beneficial for their meat and eggs and have been the focus of poultry breeders in recent decades. Egg quality traits are usually divided into external (such as shell quality and egg weight) and internal (like yolk and albumen parameters) traits. Shell characteristics are important factors to determine egg quality. The breakage of quail eggs can be occurred in various processes such as collection, packaging, and transportation or in the setter and hatcher devices, and leads to serious economic problems for the breeders in the poultry industry. The size and weight of the quail egg are important factors in the marketability of this product. From an economic point of view, the yolk is the most valuable part of the egg. The yolk is a concentrated source of nutrients, as well as it has a significant effect on the weight of the chicken. The ratio of yolk to white in quail eggs has been reported to be 35 to 65, which is higher in comparison to laying hens. Egg quality can be affected by different factors such as genotype, breed, strain, age, management, nutrition, temperature, and illness. Although there have been many studies to determine the environmental factors on traits related to egg quality in quail, there are few studies to investigate the effect of genetic factors and different mating systems on the occurrence of these traits. Therefore, the present study was conducted to estimate genetic parameters of external and internal egg quality traits in wild and white strains of Japanese quails.

A total number of 570 laying quails were obtained from pure and cross-mating groups of wild and white Japanese quails. The base population was divided into four mating groups including two pure and two crossed mating groups (group 1: wild male × wild female; group 2: white male × wild female; group 3: wild male × white female, and group 4: white male × white female). The studied traits included external (egg weight, length, and width, shell weight and thickness, and egg shape index) and internal (yolk weight, albumen weight, yolk index, albumen index, and internal egg quality unit) egg quality traits. The effects of hatch and mating groups on traits related to egg quality were investigated. The means of traits related to external and internal egg quality were compared using the Duncan test. (Co)Variance components and genetic parameters of traits related to external and internal quality traits were estimated by multiple trait animal models and restricted maximum likelihood using ASREML software.

The effect of the hatch on egg weight, shell weight, and albumen weight was significant (P<0.05) and the eggs from the second and third hatches showed higher egg weight, shell weight, and albumen weight in comparison to the first hatch (P<0.05). The difference between mating groups was not significant (P>0.05) except for albumen and egg weights. The laying quails from the pure white mating group showed lower albumen and egg weights (P<0.05). The heritability estimates for traits related to external egg quality varied from 0.16 (egg shape index) to 0.39 (egg weight). These estimates for traits related to internal egg quality ranged from 0.10 (internal quality unit) to 0.31 (yolk weight). Genetic correlations were estimated from -0.33 (between egg length and egg shape index) to 0.71 (between egg length and width) for traits related to external egg quality, and from -0.37 (between yolk weight and yolk index) to 0.71 (between albumen weight and albumen height) for traits related to internal egg quality, respectively. Phenotypic correlations varied from -0.32 (between egg length and egg shape index) to 0.61 (between egg length and width) for traits related to external egg quality, and from 0.11 (between yolk index and albumen height) to 0.59 (between the internal quality unit and albumen height) for traits related to internal egg quality, respectively.

Heritability estimates for traits related to egg quality were moderate which indicates the significant effect of additive genes on the occurrence of these traits. Positive genetic correlations between egg weight and traits related to external egg quality, as well as appropriate genetic correlations between traits related to internal egg quality showed that selection based on some egg traits like egg weight and internal egg unit can effectively lead to the improvement of other egg quality traits.