Time trend in genetic parameters of production traits in IWH and IWI lines of White Leghorn under reciprocal recurrent selection for part period egg production
R.K.S. BAIS, M.C. KATARIA, D.C. JOHARI, D. SHARMA AND R.C. HAZARY
Division of Avian Genetics & Breeding
Central Avian Research Institute, Izatnagar- 243 122 (UP)
The data on 4760 & 3155 pullets of IWH and IWI lines produced from 244, 235 sires & 928, 783 dams, respectively were analyzed using regression analysis for time trends in genetic parameters of production traits over six generations of reciprocal recurrent selection for part period egg production up to 280 days of age. The regression coefficients of heritability estimates for egg production were very low in magnitude and non-significant in both the lines. While heritability from sire component showed a slightly increasing trend over generations, the heritability from dam and sire plush dam components showed a declining trend in both the lines. Having a wide variation in the direction of trend among different traits and components, the regression coefficients of heritability on generation number were non-significant for almost all the correlated traits under study in both the lines. However, the regression of heritability estimated from sire plush dam component of variance for 20 week body weight (0.048± 0.017) in IWH and for egg weight (0.071± 0.009) in IWI lines were found to be significant (P < 0.05) and positive. The additive genetic variance for egg production in both the lines showed a non- significant change over generations and all the regression coefficients were positive. Except for 20 week body weight (1014.40± 261.04) in IWH, all other regression coefficients of additive genetic variance on generation number for different correlated traits in both the lines were non-significant. With a negative regression for age at sexual maturity, the trend for all other correlated traits was positive in both the lines. The regression coefficients for genetic correlation (sire component) of egg production with 40 week body weight in IWH and with age at sexual maturity in IWI line were found to be significant. All the remaining regressions in both the lines were non-significant with a wide variation in the direction of trend.