Estimates of (co)variance components and genetic parameters for body weights and first greasy fleece weight in Bharat Merino sheep

Abstract

(Co)variance components and genetic parameters of weight at birth (BWT), weaning (3WT), 6, 9 and 12 months of age (6WT, 9WT and 12WT, respectively) and first greasy fleece weight (GFW) of Bharat Merino sheep, maintained at Central Sheep and Wool Research Institute, Avikanagar, Rajasthan, India, were estimated by restricted maximum likelihood, fitting six animal models with various combinations of direct and maternal effects. Data were collected over a period of 10 years (1998 to 2007). A log-likelihood ratio test was used to select the most appropriate univariate model for each trait, which was subsequently used in bivariate analysis. Heritability estimates for BWT, 3WT, 6WT, 9WT and 12WT and first GFW were 0.05 6 0.03, 0.04 6 0.02, 0.00, 0.03 6 0.03, 0.09 6 0.05 and 0.05 6 0.03, respectively. There was no evidence for the maternal genetic effect on the traits under study. Maternal permanent environmental effect contributed 19% for BWT and 6% to 11% from 3WT to 9WT and 11% for first GFW. Maternal permanent environmental effect on the post-3WT was a carryover effect of maternal influences during pre-weaning age. A low rate of genetic progress seems possible in the flock through selection. Direct genetic correlations between body weight traits were positive and ranged from 0.36 between BWT and 6WT to 0.94 between 3WT and 6WT and between 6WT and 12WT. Genetic correlations of 3WT with 6WT, 9WT and 12WT were high and positive (0.94, 0.93 and 0.93, respectively), suggesting that genetic gain in post-3WT will be maintained if selection age is reduced to 3 months. The genetic correlations of GFW with live weights were 0.01, 0.16, 0.18, 0.40 and 0.32 for BWT, 3WT, 6WT, 9WT and 12WT, respectively. Correlations of permanent environmental effects of the dam across different traits were high and positive for all the traits (0.45 to 0.98).

<b>Genetic components of birth weight of texel sheep reared in extensive system

“…The phenotypic variance found herein was superior to those reported by Gowane et al (2010), for Bharat Merino sheep (0.347). Nevertheless, they obtained a residual variance of 0.260, with consequent estimates of direct additive and maternal permanent environmental variances of 0.017 and 0.067, respectively.…”

“…However, the one that best fit the data by the AIC and, consequently, was selected to present the genetic components was model 3. Gowane, Chopra, Prince, Paswan and Arora (2010), who found the best fit to the data for the model that considered direct additive and maternal permanent environmental effects. Gowane et al (2010) reported that several studies failed to partition the maternal additive and maternal environmental effects due to the requirement of repeated records for the sheep and, consequently, larger data volume.…”

“…In the study of these authors, estimates of the heritability coefficient and the phenotypic variance attributed to the permanent maternal environment were 0.05 and 0.19, respectively. Gowane et al (2010) attributed their findings to the poor nutritional level in which the sheep were managed, giving rise to a wide environmental variation, with a great importance of the effect of permanent environment of the mother on the weight of the lambs at birth.…”

Estimates of (co)variance components and genetic parameters for body weights and growth efficiency traits in the New Zealand white rabbit

“…The maternal heritability (m 2 ) for different body weight traits showed a decreasing trend with the advance of age. Gowane et al (2010) also reported that the maternal genetic effects expressed during gestation and lactation are expected to have a diminishing influence on weight as the kits grow. Higher importance of maternal effect over additive genetic effect on the post weaning growth traits in rabbits had been reported earlier (Ferraz et al, 1992;Lukefahr et al, 1993).…”

Genetic Parameter Estimates for Growth and Reproductive Trait of Sheep for Genetic Improvement and Designing Breeding Program in Ethiopia: A Review

“…Small ruminants play a major role for strengthening the backbone of rural economy; especially sheep are integral to the cultural, social and economic livelihood of the rural farmers [1]. The profitability of a sheep production system is determined by both fertility and production traits [2].…”