(Co)variance components, genetic parameters and trends for average daily gain in Muzaffarnagari sheep of India

Abstract

The aim of present investigation was to estimate variance and covariance components, genetic parameters and genetic, phenotypic and environmental trends of Muzaffarnagari sheep for a period of 27 years (1991-2017). Phenotypic data was collected from Central Institute for Research on Goats, Makhdoom. The traits analyzed under present study were average daily gain from birth to 3 months of age (ADG1), average daily gain from 3 to 6 months of age (ADG2), average daily gain from 6 to 9 months of age (ADG3), average daily gain from 9 to 12 months of age (ADG4) and average daily gain from 3 to 12 months of age (ADG5). Sex, season, year of lambing, parity and type of birth were included as fixed effects for mixed model analysis. Six animal models with different combinations of direct and maternal genetic effects were fitted by restricted maximum likelihood method using Wombat software. Bayesian information criterion was utilized for determining best model for all traits. Model 3 was obtained as the best model for all traits. Direct heritability estimates of ADG1, ADG2, ADG3, ADG4 and ADG5 are 0.37, 0.45, 0.25, 0.26 and 0.41 respectively and their respective maternal heritablilities were 0.08, 0.15, 0.09, 0.07 and 0.16. Negative covariance was observed between direct and maternal effects for all traits. The genetic and phenotypic correlation among the traits ranged from -0.59 (ADG1-ADG3) to 0.52 (ADG2-ADG5); -1 (ADG2-ADG4) to 0.50 (ADG2-ADG5) respectively. Overall genetic, phenotypic and environmental trends for all the traits were in desired direction with few negative estimates. Although desired genetic improvement has been obtained through selection, it can be further hastened, if hampering effect of environment is taken care of. Results shows the importance of maternal effects in influencing the traits studied.