The effects of ewe live weight and body condition score around mating on production from four sheep breeds in extensive grazing systems in Uruguay

Abstract

AbstractEwe 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 3-and 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.