To ensure breeding ewes can reproduce every year it is important that ewe fat score is maintained during pregnancy and lactation, especially for ewes producing twins.

While the ewe will do her best to meet the increased energy demands through increasing her intake of feed, this won’t always meet the demands of the foetus, particularly during late pregnancy and early lactation.

The amount of protein and energy taken by the foetus can leave the ewe without enough for herself, resulting in the ewe’s nutritional requirements being met by mobilising her internal fat and muscle stores.

The timing and degree of mobilisation of a ewe’s energy reserves will vary according to the quality and quantity of available feed, stage of pregnancy, and whether she is carrying single or twin foetuses.

The graph demonstrates the changes in maternal weight of the ewes using data collated from the three NSW Lifetime Wool paddock-scale sites from joining in 2004.

The change in maternal weight relative to the dry ewes in high and low nutrition groups represent the degree to which maternal body reserves were mobilised to meet the demands of pregnancy and lactation.

The negative deviations (measured in kilograms, see top graph) indicate that the dry ewes were lighter at joining than those ewes that conceived, while positive values indicate the pregnant ewes had a lower maternal liveweight than the dry ewes and were mobilising their own body reserves to provide the energy and protein required by the growing foetus.

In the high nutrition group single and twin bearing ewes had essentially the same maternal weight as the dry ewes to day 50 of pregnancy, but by day 78 they were both lower relative to the dry ewes and had started to mobilise their body reserves.

The maternal liveweight of the single and twin bearing ewes was similar to midpregnancy but began to diverge at day 103 from joining with the difference increasing over time.

This reflects the fact the twin bearing ewes must mobilise more of their body reserves to meet the energy requirements of their two foetuses.

This pattern was also evident in the low nutrition group (bottom graph), but ewes in this group, both single and twin bearing, began to mobilise their body reserves about 4 weeks earlier than high nutrition ewes.

Pregnancy toxaemia is the most noticeable consequence of the ewe metabolising her own energy reserves to satisfy the demands of her foetus.

The by-products of mobilising body reserves (ketones) - as well as a reduced energy supply - cause the ewe to become sick and show signs of the disease.

However other production consequences will also occur, including reduced wool cut and a decreased likelihood of conception at her next joining if after weaning the ewe can’t regain the energy and protein reserves mobilised during pregnancy and lactation.

Contact Sue Hatcher, Orange, (02) 6391 3861, sue.hatcher@dpi.nsw.gov.au