Comparison of heritabilty estimates from time series and least squares adjustments in Sahiwal cattle

Abstract

The data on 594 first lactation records of Sahiwal cows spread over 46 years (1961–2006) were analyzed by least squares and time series analyses for ascertaining correction factors to adjust the data for non-genetic factors to estimate heritability of first lactation traits. The traits considered were, age at first calving (AFC), first lactation total milk yield (FLTMY), first lactation 305-day or less yield (FL305DMY), first lactation length (FLL), first dry period (FDP), first service period (FSP) and first calving interval (FCI). A least-squares model incorporating 15 periods (3 years each), 12 months and AFC as co variable was fitted for all the traits except for AFC (Set-1). Least squares model comprising months, exact periods (3–7 years for various traits) and AFC as co variable comprised Set-III and Set- IV incorporated data adjusted by AFC, exact periods (3–7 years) and by monthly indices derived from time series analysis. The data were adjusted for significant non-genetic factors to estimate heritability from all the four sets. Higher estimates of heritability of majority of the traits from data adjusted by monthly indices and exact periods derived from time series analysis as compared to least squares adjustments revealed that the correction factors derived from time series analysis seem to be more appropriate to adjust the animal breeding data for non-genetic factors in Sahiwal cattle.