Effect of strain and age on the thick-to-thin albumen ratio and egg composition traits in layer hens

Much attention has been paid to the proportion of thick albumen of eggs in layer production in recent decades, owing to economics, appearance and consumption. In this study, we investigated the effect of strain and age on the ratio of thick-to-thin white and relative egg composition traits in two different layer populations with 770 birds in total at 30, 40 and 50 weeks of age. Eggs were collected from the D3 and R2 strains to measure egg composition traits for 3 successive days at each experimental week. The results showed that the egg weight, albumen height and Haugh unit of eggs in the D3 strain were significantly (P < 0.05) higher than those in the R2 strain at every experimental week, whereas the yolk percentage and the thick-to-thin white ratio of eggs were significantly (P < 0.05) lower in D3 as compared with R2. Furthermore, the albumen height and Haugh unit significantly decreased (P < 0.05) from 30 to 50 weeks of age in the D3 and R2 strains. Additionally, positive correlations were found between the thick-to-thin white ratio and egg weight in the two strains at 50 weeks of age. Significant (P < 0.05) correlations of the thick-to-thin albumen ratio were also found at 30, 40 and 50 weeks of age in both two strains. The results indicated that the thick-to-thin white ratio was a relatively stable trait and might be used as a promising index for evaluating egg composition in future chicken breeding.