The importance of accounting for maternal genetic effects in Australian fine-wool Merino breeding

Abstract

(Co) variances for greasy fleece weight (GFW), clean fleece weight (CFW), mean fibre diameter (MFD), staple strength (SS), coefficient of variation of fibre diameter (CVFD), birthweight (BW), weaning weight (WW), and yearling weight (YW) were estimated for 5108 Australian Merino sheep from the CSIRO Fine Wool Project, born between 1990 and 1994. Covariances between these traits and number of lambs weaned per ewe joined (NLW) were also estimated. Significant maternal genetic effects were found for GFW, CFW, BW, WW, and YW. Estimates of heritability were biased upwardly when maternal effects were ignored. The maternal heritability estimates for GFW, CFW, BW, WW, and YW were 0.17, 0.15, 0.38, 0.28, and 0.13, respectively. Maternal effects were not important for MFD, CVFD, SS, and NLW. Direct-maternal genetic correlations within each fleece weight and bodyweight trait were estimated to be moderately negative (–0.26 to –0.48). The effect of ignoring maternal genetic effect was explored using selection index theory. Accounting for the maternal effects in both the selection criteria and breeding objective increased the overall response by 14.3%, 4.8%, 2.6%, 1.4%, and 0.0% in 3, 6, 12, 20 and 30% micron premium scenarios, respectively, compared with when the maternal effects were only included in breeding objective. Complete ignorance of the maternal effects led to overestimation in overall response of 2.8–35.7% for different micron premium scenarios in contrast to when the maternal effects were ignored in the selection index weight, but were included in the breeding objective. The results indicate that the maternal genetic effects of fleece weight and bodyweight should be considered in Merino breeding programs.

Genetic parameter estimation of 16-month live weight and objectively measured wool traits in the Tygerhoek Merino flock

“…Maternal correlations were 0.84 between LW and GFW, 0.46 between LW and CFW, 0.85 between fleece weights, 0.08 between GFW and FD and 0.19 between CFW and FD. The maternal correlation was accordingly high (0.98) between GFW and CFW in Australian Merinos (Asadi Fozi et al, 2005).…”

“…Several studies reported significant maternal effects for LW, GFW and CFW for various sheep breeds (Asadi Fozi et al, 2005;Cloete et al, 2005;Safari et al, 2005). In contrast, Vaez Torshizi et al (1996) reported no significant maternal effects for any of the corresponding objective wool traits beyond 12 months of age.…”

“…In addition, Van Wyk et al (2003) and Safari et al (2007b) partitioned the dam environmental variance into a temporary litter effect and a permanent environmental effect (the correspondence of records of the same dam across breeding seasons) to accurately reflect the contribution of the respective components. Furthermore, Asadi Fozi et al (2005) reported the importance of including maternal genetic effects for fleece traits in Merino breeding programmes.…”

Genetic parameters for yearling wool production, wool quality and bodyweight traits in fine wool Merino sheep

“…While there appears to be a strong negative correlation between direct and maternal genetic effects for fleece weight, this correlation is closer to zero for bodyweight. Asadi Fozi et al (2005) showed that accounting for maternal genetic effects in Merino breeding objectives led to more 0.68 ± 0.09 0.60 ± 0.13 0.58 ± 0.12 0.54 ± 0.08 0.09 ± 0.02…”

“…In addition, preliminary estimates of heritabilities and correlations from subsets of the complete dataset of the Fine Wool Project flock have been published by Swan et al (1995), Purvis and Swan (1997) and Asadi Fozi et al (2005). While collectively these studies have shown that fine wool genetic parameters are not substantially different to medium wool parameters, the complete Fine Wool Project dataset now provides us with the ability to investigate this issue with greater precision.…”