GENETIC AND PHENOTYPIC CORRELATIONS OF TOTAL WEIGHT OF LAMB WEANED WITH BODY-WEIGHT, CLEAN FLEECE WEIGHT AND MEAN FIBER DIAMETER IN 3 SOUTH-AFRICAN MERINO FLOCKS

Data collected on three South African Merino flocks were used to estim ate genetic and phenotypic correlations of total weight of lamb weaned over three parities (TWW) with two-tooth body weight at 14 to 17 mont hs of age (BW), clean fleece weight (CFW) and mean fibre diameter (MFD ). The flocks included were maintained under widely divergent environm ental conditions, and included the Tygerhoek Merino flock (n = 1360), the Grootfontein Merino stud (n = 1535) and the Klerefontein Merino fl ock (n = 1971). The arid environment of Klerefontein supported mean (/-SD) performance levels of 32.0+/-5.6 kg, 2.6+/-0.7 kg, 19.8+/-1.9 mu m and 37.7+/-21.7 kg for BW, CFW, MFD and TWW respectively. Performan ce levels under more favourable environmental and less extensive condi tions at Grootfontein were markedly higher (respectively 42.8+/-7.0 kg , 4.8+/-1.1 kg, 23.0+/-2.1 mu m and 91.1+/-35.9 kg), with Tygerhoek ge nerally intermediate in this regard. Phenotypic correlations of TWW wi th BW varied from 0.15+/-0.04 at Tygerhoek to 0.32+/-0.02 at Klerefont ein. Corresponding genetic correlations were positive and high, rangin g from 0.67+/-0.13 at Grootfontein to 0.80+/-0.04 at Tygerhoek. Phenot ypic correlations of TWW with CFW and MFD were relatively low (r(p) < 0.10). The genetic correlations of TWW with CFW were variable, ranging from 0.06+/-0.11 at Klerefontein to 0.41+/-0.11 at Tygerhoek. Corresp onding correlations with MFD were more stable, ranging from 0.18+/-0.1 3 at Tygerhoek to 0.26+/-0.20 at Grootfontein. It was concluded that p rogress in all these economically important traits would be feasible i n a well-designed breeding programme for South African Merino sheep. T he estimation of further, more precise, genetic correlations from larg er data sets may also be regarded as a priority for the Merino industr y. (C) 1998 Elsevier Science B.V.