Estimation of (co)variance components and genetic parameters of greasy fleece weights in Muzaffarnagari sheep

Abstract

Variance components and genetic parameters for greasy fleece weights of Muzaffarnagari sheep maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 29 years (1976 to 2004) were estimated by restricted maximum likelihood (REML), fitting six animal models including various combinations of maternal effects. Data on body weights at 6 (W6) and 12 months (W12) of age were also included in the study. Records of 2807 lambs descended from 160 rams and 1202 ewes were used for the study. Direct heritability estimates for fleece weight at 6 (FW6) and 12 months of age (FW12), and total fleece weights up to 1 year of age (TFW) were 0.14, 0.16 and 0.25, respectively. Maternal genetic and permanent environmental effects did not significantly influence any of the traits under study. Genetic correlations among fleece weights and body weights were obtained from multivariate analyses. Direct genetic correlations of FW6 with W6 and W12 were relatively large, ranging from 0.61 to 0.67, but only moderate genetic correlations existed between FW12 and W6 (0.39) and between FW12 and W12 (0.49). The genetic correlation between FW6 and FW12 was very high (0.95), but the corresponding phenotypic correlation was much lower (0.28). Heritability estimates for all traits were at least 0.15, indicating that there is potential for their improvement by selection. The moderate to high positive genetic correlations between fleece weights and body weights at 6 and 12 months of age suggest that some of the genetic factors that influence animal growth also influence wool growth. Thus selection to improve the body weights or fleece weights at 6 months of age will also result in genetic improvement of fleece weights at subsequent stages of growth.

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

“…This is indicative of the fact that post-3WT has almost no carryover maternal effect and indicates the importance of impact of animal's own genotype for body weight (BW) at post-weaning stage. Similar reports where maternal effects were found to be declining with the advancement of age were given by Maria et al (1993), Mortimer and Atkins (1994), Tosh and Kemp (1994), Mandal et al (2006b) and Mandal et al (2009). As discussed earlier, partitioning of the total maternal effect into its direct and permanent environmental components was difficult for post-3WTs.…”

“…Yazdi et al (1997) in Baluchi sheep and Ozcan et al (2005) in Turkish Merino sheep (0.08 for GFW in the first shearing, that is, at the average age of 18 months). However, higher estimates were reported by Snyman et al (1996) in Merino sheep (0.20) and Mandal et al (2009) in Muzaffarnagri sheep (0.14).…”

“…These estimates correspond with the review by Safari et al (2005). In this study, phenotypic correlations of GFW with 6WT and 12WT were higher than the estimate by Yazdi et al (1997) for Baluchi sheep at 6 months of age (0.02) and similar to estimates by Mandal et al (2009) for Muzaffarnagri sheep at 6 and 12 months of age (0.36 and 0.39). Estimate of genetic and phenotypic correlations of 3WT with GFW are 0.16 and 0.52, respectively.…”

“…Other estimates were within the range of values reviewed by Safari et al (2005). Current estimates for genetic correlation of GFW with 6WT and 12WT were lower than the estimates by Yazdi et al (1997) in Baluchi sheep at 6 months of age (0.41) and by Mandal et al (2009) in Muzaffarnagri sheep at 6 and 12 months of age (0.61 and 0.67). Corresponding permanent environmental correlation due to dam for GFW with live weights at different ages were moderate in this study (0.45 for GFW and 9WT to 0.66 for GFW and 3WT).…”

Quantitative trait loci associated with pre-weaning growth in South African Angora goats

“…Genetic correlations of respectively 0.69 and 0.81 between weight at 3 months, weight at 6 months and weight at 12 months were found in Menz sheep by Gizaw et al (2007). Estimates of 0.80 were also reported by Mandal et al (2009) between weight at 6 months and yearling weight in Muzaffarnagari sheep, and 0.73 between weights at weaning and yearling age in Merino sheep (Swan et al, 2008). These correlations indicate that selection for increased birth and weaning weight should result in higher mature weight and improved reproduction rates of young does.…”