Rearing performance of Merino, Sa Mutton Merino and Dormer ewes in relation to live mass, reproduction and pelvic dimensions.
Live mass, reproduction and pelvic dimensions (determined mainly by radiographic pelvimetry at more than 4 years of age) were obtained for ewes of the Langgewens Merino flock (n = 102), ewes of the Tygerhoek Merino flock (n = 434) and ewes of the Elsenburg SA Mutton Merino (n = 130) and Dormer flocks (n = 130). Ewes were classified as "good" or "poor" according to their rearing ability (ewes rearing/ewes lambed--Er/El) and rearing performance (lambs reared/lambs born--Lr/Lb) averaged over at least 4 lambings in 4 to 5 lambing opportunities. Good ewes tended to be lighter than poor ewes at 18 months (Merino) or weaning (SA Mutton Merino and Dormer). This tendency was also reflected in live mass at the time of radiography, being significant (P < or = 0.01) in Tygerhoek Merinos. Good and poor ewes were similar with regard to fecundity (lambs born/ewes lambed) and lambing percentage (lambs born/ewes joined), but differed (P < or = 0.01) markedly with regard to rearing percentage (lambs reared/ewes joined), Er/El and Lr/Lb. Poor ewes constituted 6.9 to 21.7% of the available ewes in the respective flocks, and were involved in 38.9 to 56.9% of all cases of rearing failure. Good ewes had smaller (P < or = 0.07) transverse pelvic diameters than poor ewes in the Langgewens Merino and Elsenburg Dormer flocks, while rearing performance was independent of transverse diameter in the other two flocks. Good ewes generally had larger conjugate pelvic diameters than poor ewes, significantly (P < or = 0.05) so in the case of the 2 Merino flocks.
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Elsenburg Agricultural Centre, Republic of South Africa.
D000818:Animals; D001835:Body Weight; D001947:Breeding; D005260:Female; D005298:Fertility; D010384:Pelvic Bones / Q000033:anatomy & histology*; D010387:Pelvimetry / Q000662:veterinary; D010388:Pelvis / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011247:Pregnancy; D011859:Radiography; D012756:Sheep / Q000033:anatomy & histology*