Precision in estimation of heritability

Abstract

The various effects such as year and period of calving, season of calving, parity and lactation length were included in the model. The effects of year of calving, season of calving and parity dam were significant (P<0.001) for the various traits. The estimates of heritability using 16 linear models showed a wide range of variation. The values ranged from 0.062 to 0.439 for total milk yield, 0.075 to 0.482 for 305 days milk yield, 0.085 to 0.589 for peak yield and 0.06 to 0.432 for daily milk yield. The inclusion of lactation length in the model as a co-variable reduces the error mean squares. thereby increasing the efficiency (R²value) of the model. It also increased the heritability estimates, however, it reduced the mean square due to sires. The R² value was maximum for the model, which included year, season, parity, sire within year and regression of lactation length (linear and quadratic) for all traits. The results indicated that environmental factors adjustment affected the estimates of heritability and the magnitude of such variation usually depended upon the number of adjustments made.