Genetic and phenotypic correlations of total weight of lamb weaned with body weight, clean fleece weight and mean fibre diameter in three South African Merino flocks

Abstract

Listen

Translate article

Data collected on three South African Merino flocks were used to estimate genetic and phenotypic correlations of total weight of lamb weaned over three parities (TWW) with two-tooth body weight at 14 to 17 months of age (BW), clean fleece weight (CFW) and mean fibre diameter (MFD). The flocks included were maintained under widely divergent environmental conditions, and included the Tygerhoek Merino flock ( n=1360), the Grootfontein Merino stud ( n=1535) and the Klerefontein Merino flock ( 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 μm and 37.7±21.7 kg for BW, CFW, MFD and TWW respectively. Performance levels under more favourable environmental and less extensive conditions at Grootfontein were markedly higher (respectively 42.8±7.0 kg, 4.8±1.1 kg, 23.0±2.1 μm and 91.1±35.9 kg), with Tygerhoek generally intermediate in this regard. Phenotypic correlations of TWW with BW varied from 0.15±0.04 at Tygerhoek to 0.32±0.02 at Klerefontein. Corresponding genetic correlations were positive and high, ranging from 0.67±0.13 at Grootfontein to 0.80±0.04 at Tygerhoek. Phenotypic 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. Corresponding correlations with MFD were more stable, ranging from 0.18±0.13 at Tygerhoek to 0.26±0.20 at Grootfontein. It was concluded that progress in all these economically important traits would be feasible in a well-designed breeding programme for South African Merino sheep. The estimation of further, more precise, genetic correlations from larger data sets may also be regarded as a priority for the Merino industry.