Studies on small ruminant breeds with inherent differences in fibre production and ewe productivity 1. Relationship between ewe

摘要

Ewe productivity, as affected by varying wool production potential in different environments was studied in three woolled sheep flocks. Production and reproduction data collected in the Carnarvon Afrino Flock (AC) between 1979 and 1992, as well as data of the Carnarvon Merino Flock (MC) collected between 1962 and 1983 were used to represent production in a semi-desert environment. Similar data collected in the Grootfontein Merino Stud (MG) between 1966 and 1993 were used to represent production under favourable nutritional conditions. Only data concerning the first three lambing opportunities of 609, 2234 and 1616 ewes of AC, MC and MG respectively, were included in the analysis. Wool production potential (WPP), defined as wool produced per kg of body weight from 6 to 18 months of age was 4.21, 8.15 and 11.24% for AC, MC and MG respectively. Ewe productivity (EP), defined as total weight of lamb weaned over the first three lambing opportunities was 116.8, 38.8 and 90.2 kg for the respective flocks. Within all three flocks, EP was negatively related (p < 0.01) to WPP. It is concluded that selection programmes with the net result of increasing WPP may have a detrimental effect on ewe productivity irrespective of breed and environment. Apparently, the concept of adaptation to adverse environmental conditions needs to be duly considered in selection programmes of sheep. The provision of optimum nutritional conditions, such as diets with high levels of grain, to stud animals should also be reconsidered, especially where the progeny of these animals have to produce under less favourable conditions.