Last update: August 12, 2011 03:09:48 PM E-mail Print




J.J. Olivier & Margaretha A Snyman

Grootfontein Agricultural Development Institute, Middelburg 5900



To optimize breeding plans, (co)variance components of the economically important traits must be known, at least to proportionality. Although the Merino is the major wool producing breed in South Africa, only a few suitable data sets for genetic parameter estimation are available. One of these data sets was obtained from a selection experiment carried out at the Carnarvon Experimental Station over a period of 20 years. Records on weaning weight (WW; n=8480), six month body weight (W6; n=6761), six month greasy fleece weight (GFW6; n=6753), 18 month body weight (W18; n=7407), clean fleece weight (CFW18; n=7371) and mean fibre diameter (MFD18; n=7396) were available. Variance components resulting from direct additive genetic effects, maternal additive genetic effects, maternal permanent environmental effects, as well as the relationship between direct and maternal effects were estimated using derivative-free Restricted Maximum Likelihood procedures. A single trait animal model was applied for each trait. Fixed effects for year-season of birth, sex and rearing status of the lamb, age of dam and age of lamb were included in the respective models. Direct heritabilities (h2a) of 0.141 ± 0.021, 0 .184 ± 0.024 and 0.428 ± 0.029 were estimated for WW, W6 and W18 respectively. For the various fleece traits, h2a of 0.195 ± 0.036 for GFW6, 0.254 ± 0.034 for CFW18 and 0.617 ± 0.020 for MFD18 were estimated. Maternal heritability (h2m) decreased from 0.108 ±0 0.023 at WW to 0.068 ± 0.022 at W6 and 0.036 at W18. The h2m for CFW18 (0.028 ± 0.018) was also lower than the 0.058 ± 0.027 estimated for GFW6. Maternal effects had no influence on MFD18 (h2m = 0.008). Maternal permanent environmental effects (c2 had a small influence on WW (0.051 ± 0.017), W6 (0.029 ± 0.017) and GFW6 (0.054 ± 0.034), but no effect on W18, CFW18 and MFD18. From these results and similar reported estimates, it is evident that the heritability of fibre diameter is higher than the current estimate (0.47) being used to construct selection indices. Furthermore, the heritability of fleece weight is lower than the value of 0.40 currently being used. It is therefore suggested that the (co)variances used for calculating selection indices on a national basis, be updated.




Proceedings 34th SASAS congress, Bloemfontein, 10-13 April