Direct and maternal (Co) variance components, genetic parameters and trends for reproduction traits 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 for reproduction traits 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 age at first service (AFS), age at first lambing (AFL) and litter size (LS). Season, year of lambing, parity and type of birth were included as fixed effects for mixed model analysis of AFS and AFL. Season, year of lambing and parity were included as fixed effects for mixed model analysis of LS. 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 1, 2 and 6 were obtained as the best model for AFS, AFL and LS respectively. The direct heritability estimates from best models were 0.004±0.04, 0.36±0.1 and 0.59±0.24 respectively for AFS, AFL and LS. The respective maternal heritability estimates for AFL and LS from best models were 0.34±0.1 and 0.16±0.01 respectively. Negative covariance was observed between direct and maternal effects for all traits. The genetic and phenotypic correlation among the traits ranged from .82 (AFS-LS) to 0.99 (AFS-AFL); 0.03 (AFS-LS) to 0.99 (AFS-AFL) respectively. Overall genetic and phenotypic trends for all the traits were in favourable direction. Negative estimates were observed for environmental trends. Desired genetic improvement obtained through selection is hampered by environmental interaction. Importance of maternal effect in influencing the traits was found in the investigation.