Abstract

The inter-generational effect of birth rank and nutrition during pregnancy was assessed by examining the reproductive success of female progeny at their first mating at 2 years of age. Fifty-six ewes born as a twin or triplet and whose dam was maintained on 2 or 6 cm sward height from mid-pregnancy to parturition were synchronised and bred to Romney rams. Pregnancy diagnosis was conducted using ultrasound on day 71 from the start of mating (P71). All ewes were maintained as one mob under commercial farming conditions throughout pregnancy. Within 12 hours of birth lambs were ear tagged, weighed and body dimensions (CRL, girth, forelimb and hind limb lengths) were recorded. Lamb live weights were also recorded at day 48 after the mid-point of lambing (L48). Fifty-one ewes lambed of the 56 ewes that were bred. Twin-born ewes had significantly longer gestation lengths (by 1.3 days) than triplet-born ewes. Singleton lambs born to triplet-born ewes were significantly (P<0.05) lighter (4.6 kg) at birth than singleton lambs born to twin-born ewes (5.1 kg). Singleton lambs whose grand-dams were maintained on 2cm pastures during pregnancy and whose dam was born as a twin had significantly (P<0.05) longer hind limbs than their counterparts whose grand dam was maintained on 6 cm and whose dam was born a triplet but they did not differ in birth weight. Dam birth rank and the nutritional treatment of their grand-dam had no significant effect on twin-lamb live weight and body dimensions at birth. These results suggest that selecting triplet ewe lambs for breeding could have detrimental effects on flock productivity. In addition a previous study involving the same animals reported triplet born ewes displayed poorer maternal behaviour. To the authors knowledge this is the first finding of this kind and could have implications for ewe selection on New Zealand farms.

RA, Corner, PR Kenyon, KJ Stafford, DM West, and ST Morris

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 434-438, 2006