Factors affecting reproduction in Merino ewes of the Tygerhoek flock

Author: S.W.P. Cloete & H.J. Heydenrych
Year: 1986
Issue: 1
Volume: 16
Page: 36 - 42

Factors affecting reproduction in Merino ewes were investigated using data of 7 917 matings of 2 258 ewes in the Tygerhoek flock during the lambing seasons of 1971 to 1984. The ewes were run in a selection trial to evaluate selection procedures for wool yield (selection for clean fleece mass as such or for SIP ratio) against a control group. The data were analysed by least squares procedures within and across ewe age groups. Reproduction traits investigated were ewes conceived/ewe mated (Ec/Em), lambs born/ewe conceived (Lb/Ec), lambs born/ewe mated (Lb/Em), and lambs weaned/ewe mated (Lw/Em). Age trends in reproduction were in agreement with literature cited. Selection for clean fleece mass and SIP ratio did not reduce reproduction, but tended to affect it advantageously. This tendency could not be related to diverging time trends when compared to the control group. Multiple-born ewes reproduced better than singles. Mating mass and Ec/Em were linearly and positively related in 2-year-old ewes, but virtually unrelated at older ages. The relationship of mating mass with Lb/Ec and Lb/Em was linear and positive throughout. The effect of mating mass on Lb/Em was partially transmitted to Lw/Em. Multiple-born ewes tended to be more responsive in terms of Lb/Ec and Lb/Em to mating mass increases than singles.



Keywords: Birth type, clean fleece mass, ewe age, mating mass, Reproduction traits, selection
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