Problems in the accurate recording of lambing data

Abstract

Continuous observations of a Merino flock comprising representatives from 15 strains or studs, lambing together in a drift system, showed that data on litter size and identity of offspring obtained at once-daily inspections were likely to be incorrect for 12% of ewes producing singles, 30% producing twins and 60% producing triplets. Correspondingly, the pedigree data for approximately 9% of single lambs, 15% of twins and 24% of triplets would be incorrect and the litter size data incorrect for another 3, 15 and 36% of singles, twins and triplets respectively. These potential errors were due to failure of ewes to keep their litters together, desertion of lambs, and lamb 'stealing' by ewes about to lamb. The use of an examination of afterbirths to resolve doubts about litter size is presented it1 an appendix. Of lambs separated from their mothers, 43% of singles, 34% of twins and 9% of triplets were reared to weaning by foster ewes; the others died. At least 19% of twin-bearing ewes in each of the main strain groups became separated from at least one twin, indicating that failure of ewes to keep their litter together during the first day or so after birth is a characteristic of Merino sheep generally. These results have important implications for the collection of lambing data in sheep breeding and husbandry experiments aimed to increase fecundity.