The reproductive performance of ewe lambs in a controlled environment

Abstract

ABSTRACTThe effects of strain, season, type of birth, age and body weight at breeding on fertility and fecundity of ewe lambs raised in a controlled environment were evaluated. Data were derived from 2776 ewe lambs of a synthetic sire strain, two synthetic dam strains and two control strains (Suffolk and Finnish Landrace breeds) mated to 719 rams over 15 breeding periods during January, May or September over 9 years. The ewe lambs were exposed to rams at a synchronized and follow-up oestrus at 6·5 to 7·5 months of age. There were significant differences among strains. Fertility and fecundity were highest for lambs of the Finnish Landrace breed, intermediate for the two synthetic dam strains and lowest for the synthetic sire strain and the Suffolk breed. Although period of breeding and season had an effect on reproductive traits, the strain differences were not consistent. Type of birth did not affect performance of lambs at the synchronized oestrus. However, overall fertility and fecundity increased progressively as the type of birth of the lambs increased from singles to triplets and greater. Increased age and body weight at the synchronized oestrus had a significant and positive effect on fertility and fecundity.