Heritability estimates of external egg quality traits of Exotic Laying Chickens under the influence of age variance in the tropics

The present research was designed to examine heritability estimates of egg length, egg breadth and egg shape index under the influence of age variance for Bovan Nera Black laying chicken sat 25, 51, 72 weeks and overall mean ages of the bird. For this purpose thirty birds were selected from the flock of layers in the Babcock University Teaching and Research Farm. A total of thirty (30) eggs were collected daily from the birds continuously for five (5) days of egg production, at each age 25, 51 and 72 weeks. The total number of eggs collected at each age was 150 and 450 for the total of three age periods. Data were collected on egg production traits for egg length, egg breadth and egg shape index. The mean values of the egg quality traits revealed an apparent increase for egg length 4.05–4.65 cm and egg breadth 2.47–2.66 cm with a corresponding overall mean data 4.38 cm for egg length and 2.56 cm for egg breadth; however, egg shape index recorded decrease from 61.87 to 57.19 with a corresponding overall mean of 58.92. General linear model procedure of statistical analytical system was used to obtain the variance components for the estimation of heritability. High heritability estimates were obtained when the age variance was included in the computation for overall mean and at 25 weeks for the studied traits, and at 72 weeks for egg breadth and egg shape index when the age variance was excluded while low estimates were registered at 51 for all traits, and at 72 for egg length and with the corresponding overall mean for all traits when the age variance was excluded from the computation. The heritability estimates from different egg quality traits were low to high. Since some of the traits recorded low heritability values, these traits can be improved by mass selection thereby culminating into egg production with optimal quality. Keywords: Peak egg production, Age variance, Egg quality traits, Genetic potential, Heritabilit