Ewe live iveights were recorded 4 weeks prior to mating, at the beginning of mating and 22 to 23 days later over a period of 3 years in a flock of some 300 breeding ewes comprising approximately equal numbers of Australian Merino, Ideal (Polwarth), Merilin and Corriedale breeds in a pastorally based grazing system in Uruguay. Multiple-bearing ewes were generally heavier than single-bearing ewes which in turn were heavier than ewes which did not conceive, these differences being greatest in 3-and 4-year-old ewes (i.e. in their second and third breeding seasons). Body condition scores of non-pregnant ewes were lower than those of pregnant ewes, particularly in the 3and 4-year-old age groups. Ewe live weights achieved prior to, during and at the end of the mating period and the body condition score achieved 4 weeks prior to mating all had significant influences on the number of lambs born (P < 0-01) but there were no significant effects of changes in either live weight or body condition over the 4 weeks prior to mating or during the mating period. The effect of body condition score over the range from 2-0 to 4-0 was to increase the proportions of single-and multiple-bearing ewes and to decrease the proportion of non-pregnant ewes such that the number of lambs born per ewe mated increased from 0-94 to 1-38. Fleece weights differed significantly between breeds, Corriedales having the heaviest fleeces and Merilins the lightest (4-26 and 3-22 kg respectively). Wool production was also significantly and positively affected by age (P < 0-01) and by ewe weight at mating (P < 0-01). The results demonstrate the importance of giving preferential nutritional treatment to younger ewes to ensure a satisfactory subsequent lambing performance and improved wool production.
Differences in the productivity of twin- and single-bearing, spring-lambing Corriedale ewes and their progeny were studied over 8 years at the Experimental Station, Faculty of Agriculture, Paysandu, Uruguay. Lambing ewes, grazing improved pastures during late pregnancy and early lactation, produced 9.7% less wool than dry ewes, gestation and lactation accounting for 4.5 and 5.2% of this difference, respectively. No difference in wool production was found between ewes rearing 1 or 2 lambs. Twin-born sheep produced 1.8% less wool than singles, but the difference decreased with age. Twin-born ewes had a 7.5% higher lambing rate than single-born ewes, but the mortality rate among their lambs was higher (37.1 v. 20.4%). The liveweight of single-born sheep was higher than that of twins by 20.4%, 16.0% and 11.4% at marking, weaning and 11 1 days of age, respectively. We suggest that the difference in productivity between twin- and single-bearing ewes, and their lambs, can be minimised by adequate nutrition in late pregnancy and early lactation.
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