Effect of Genotype, Age of Layer and their Interaction on Egg Quality Characteristics of Egg-lay Chickens.

Abstract

A study was carried at the Papua New Guinea University of Natural Resources and Environment to evaluate the effects of genotype and age of laying bird on egg quality traits of egg-layer chickens. A total of 180 eggs were collected from three genotypes at 56 and 68 weeks of age. The three genotypes were Australorp and F1 and F2 crosses derived from crossing an Australorp sire line with the Shaver Brown commercial dam line. Thirty eggs from each genotype and age group were evaluated for external and internal egg quality characteristics. The traits measured were egg weight (EW), egg shape index (ESI), shell weight (SW), shell percentage (SP), yolk weight (YW), yolk percentage (YP), albumen weight (AW), albumen percentage (AP), albumen height (AH) and Haugh unit (HU). The effects of genotype were found to be significant (P<0.05) for ESI, SW, SP, YW and YP. The highest value for ESI was for the F1 and shell quality was better for the crosses than for the Australorp. By contrast, the Australorp had the highest yolk percentage of 28.77 percent compared to 27.86 and 27.30 percent for the F1 and F2 respectively. Egg and yolk weights increased significantly (P<0.05) by three and four percent respectively with increased age. Albumen quality was not influenced by differences in genotype and age. However, a genotype by age interaction was observed for AW, AP and YP. The Australorp had high AW and AP initially but these declined with increasing age compared to the crosses. The F1 had the highest YP in the beginning but the Australorp had the highest YP by week 68. The results suggest that differences in genotype and age of bird, and their interaction, may affect egg quality traits of layer chickens. Customers who buy crossbred eggs of the same weight would obtain less yolk than those who buy Australorp eggs.