Reproduction rate and viability of Merino, Nilagiri and halfbred Merino. I. Fertility, prolificacy and viability.

Lambing records from 482 Merino ewes, 533 Nilagiri ewes and 192 halfbred Merino ewes were used to estimate the number of ewes lambing per ewe inseminated, number of lambs born per ewe lambing, number of lambs weaned per lamb born and number of ewe lambs reaching joining age per ewe lamb weaned. Adult viability was studied by following through the life of 385 Merino ewes, 192 Nilagiri ewes and 61 halfbred ewes in the breeding flock from one and a half to seven and a half years of age. The genetic groups differed significantly for all the reproductive traits but not for adult viability. Lower values of number of ewes lambing per ewe inseminated compared to the number weaned and the number reaching joining age indicate that infertility and embryonic mortality were the main sources of loss.