Abstract

This study tested the hypothesis that in high fertility ewes, low nutrition in early to mid pregnancy could affect placental development in turn affecting foetal development, lamb birth weight and lamb survival. In 1997, 600 Finn x Romney ewes were randomised to 1 of 5 herbage allowance treatments applied over day 20 to 70 of pregnancy. Over the treatment period, mean herbage intake ranged from 0.69 to 2.04 kg DM/ewe/day resulting in ewe live weight changes of –36 to +60 g/ewe/day respectively (p<0.001). The result was a consistent but non-significant trend in birth weight with the lowest allowance ewes having single and twin lamb birth weights of 5.2 and 4.3 (SED 0.2) kg respectively. Corresponding birth weights for lambs from the highest allowance ewes were 5.3 and 4.4 kg. Lambing rate and lamb survival were not affected. In 1998, 4 nutrition treatments were applied from day 7 to 70 of pregnancy to 650 ewes randomised from either of 2 reviously generated mating weight groups. These treatments gave live weight changes of –84 to +35 g/ewe/day (p<0.001) from average herbage intakes of 0.70 to 1.96 kg DM/ewe/day. Birth weight of the single lambs (trial average 5.0 kg; SED 0.1) was not affected. However, twin lambs born from ewes from the lowest herbage allowance treatment were 0.35 kg lighter than those from the other treatments (p<0.01). Similarly, lambs born per ewes mated and lambs weaned per ewes present at lambing were also affected (p<0.05). We conclude that, in fecund ewes, nutrition in early pregnancy can affect twin lamb birth weight and lambing rate but only where the ewes are losing weight at more than 40 g/ewe/day or lose more than 4 kg from mating to mid-pregnancy.

DC, Smeaton, RW Webby, and I Tarbotton

Proceedings of the New Zealand Society of Animal Production, Volume 59, , 108-110, 1999