_____________________________________________________________________ AbstractData used for this study were collected on the Carnarvon Afrino flock from 1986 to 1998, and include data records on several subjectively assessed traits, body weight and fleece traits of 3291 animals, the progeny of 127 sires and 772 dams. Reproduction data of 686 ewes born from 1986 to 1997 were also included. The heritabilities of and genetic and phenotypic correlations among the subjectively assessed traits were estimated, as well as the genetic and phenotypic correlations of these traits with body weight, objective fleece traits and reproduction. Heritability estimates for the various subjectively assessed traits ranged from 0.06±0.02 for straightness of the top line to 0.51±0.04 for softness of fleece. Positive genetic correlations, ranging from 0.33±0.18 to 0.80±0.06 were estimated amongst the conformation traits head, front quarters, top line and hocks. High genetic correlations were estimated among the subjectively assessed fleece traits and fibre diameter, where animals with lower fibre diameter had softer fleeces, better crimp definition, their fleeces were more even, less dense and had higher creeping belly scores (the extent to which belly wool tends to creep up the side into the fleece). Estimated genetic correlations between the subjectively assessed fleece traits and reproduction were variable in sign and magnitude. The most important of these is the unfavourable genetic correlation (-0.33±0.23) between creeping belly and reproduction. The conformation traits had moderate to high genetic correlations with body weight at all ages. Of the subjectively assessed fleece traits, creeping belly score had the highest genetic correlation with body weight, ranging from -0.26±0.10 for weaning weight to -0.38±0.07 for 15-month body weight. No noteworthy phenotypic correlations were discernable between the reproductive traits and any of the subjectively assessed traits. Of the objective fleece traits, only fibre diameter had some significant phenotypic correlations with the subjectively assessed fleece traits. These were similar in sign, but smaller in magnitude than the corresponding genetic correlations. It is concluded that, with the exception of two or three traits, the subjectively assessed traits would not be negatively influenced when selection is based on the economically important production traits. It is, however, important that selection priorities be based on economic values of the traits.

This study was conducted to evaluate direct and correlated selection responses to selection for total weight of lamb weaned per ewe joined (TWW), number of lambs born (NLB), number of lambs weaned (NLW) and weaning weight (WW). Data from the Grootfontein Merino stud and the Carnarvon Merino flock were used. Estimated heritabilities for TWW, NLB, NLW and WW were 0.19, 0.23, 0.17 and 0.21 for the Grootfontein Merino stud and 0.21, 0.19, 0.16 and 0.30 for the Carnarvon Merino flock. High genetic correlations (0.89-0.98) were obtained between reproduction traits in both flocks, while the genetic correlations between WW and TWW, NLB and NLW were moderate to high (0.32-0.78). Phenotypic correlations between WW and reproduction traits were low (0.04-0.19) and phenotypic correlations between reproduction traits were high (0.71-0.96). In the Grootfontein Merino stud, approximately the same selection response (gain per generation) for TWW could be expected from direct selection (9.03 kg) as from indirect selection for NLB (9.20 kg). In the Carnarvon Merino flock, the highest selection response for TWW (6.37 kg) would be achieved by direct selection for TWW. The estimated selection responses indicate that direct selection for TWW would be the most suitable selection criterion for improving reproductive performance in flocks with a high reproduction rate where an increase in the number of lambs would be undesirable.

Global warming is predicted to have a profound effect on livestock production in developing countries. An improved understanding of the adaptation of livestock to such changing production environments is thus important, but the measurement of adaptation is complex and difficult. Proxy-indicators for adaptation, such as reproductive and production traits, however, can be used. Livestock industries have a responsibility to reduce the release of greenhouse gases (i.e. the carbon footprint) and water use (i.e. the water footprint). An effective way of decreasing the carbon and water footprints from livestock is to reduce livestock numbers and increase the production per animal. Increased production generates less greenhouse gas emissions per unit of livestock product. Proper definition of breeding objectives and trait definition is essential in implementing efficient breeding systems to cope with climate change. Sophisticated statistical models continue to support animal breeding and improvement, especially with respect to production traits. Traits linked to fertility and survival are still problematic and appropriate genetic technology to properly characterize these traits needs to be developed. Gene or marker-assisted selection may play an important role in selection for disease and parasite resistance or tolerance, since it is generally difficult to measure these traits directly. Strategies that utilize breeding values derived from genomic analyses may speed up the process of breeding animals with higher and more efficient production and that are adapted to the changing environments as a result of global warming. However, both genetic and epigenetic controls influence genetic expression and should be taken into account when formulating breeding programmes. Subsistence farmers keep livestock for multiple purposes and the formulation of breeding objectives/strategies will have to consider these dynamics. ________________________________________________________________________________

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