Managing ewes in late pregnancy
Key Points:
- Ewe condition in late pregnancy affects lamb birth weight and therefore survival.
- Lambs born from ewes with poor condition in late pregnancy will have lower production for life.
- Twin lambs are very vulnerable to poor ewe nutrition and low survival rates will occur particularly if lambing weather is poor or low feed is available to the ewe at lambing.
- Ewe mortality is affected by low nutrition in the lead up to lambing and individuals should not be below condition score 2 for lambing.
Ewe condition in late pregnancy has a major influence on the growth of the foetus which has a significant impact on birth weight and therefore survival. There are substantial penalties for not having ewes in good condition by lambing. Ewes that are below optimal condition at lambing may have a significant cost on the sheep enterprise through decreased lamb survival and progeny production. In wool flocks, poor ewe nutrition in late pregnancy influences secondary wool follicle development which directly influences the density and fineness of the fleece of the progeny.
The developing lamb:
Most of the growth of the developing lamb occurs in the last 50 days before birth. Poor nutrition at this time will negatively impact on the birth weight of the lamb (decreasing likely survival, particularly in twins) and increase the possibility of ewe mortality at birth.
Increasing ewe nutrition (gaining one condition score) during late pregnancy has a greater impact on lamb birth weight (up to 0.45 kg), than nutrition in early pregnancy. Birth weight is a key factor for lamb survival; increasing birth weight in twin Merino lambs by 0.25kg can result in a 10% increase in survival. For more information on the impacts on the impacts of nutrition on production and survival in Merinos as well as recommended condition score profiles for different times of lambing in different pasture systems please visit
www.lifetimewool.com.au.
The relationship between ewe condition at lambing and lamb survival
Figure 1. Impact of ewe condition at lambing on lamb survival and ewe mortality (source: Lifetimewool).
The ewe’s energy requirement in late lactation increases by 50% for single bearers and 80% for twin bearers by lambing. To increase her intake to meet this demand the ewe must have higher amounts or quality of pasture available or more supplements.
Managing ewe nutrition in late pregnancy
To achieve an optimum feeding plan for ewes in late pregnancy, single and twin bearing ewes can be managed to their specific feed requirements if the flock is pregnancy scanned. This is particularly useful for twinning ewes in a poor season or if there is a risk of dystocia in single ewes in good seasons. Where pregnancy status is not known it is best to either estimate the likely proportion of twinning ewes in the flock and adjust rates to match or feed to meet twinning ewes’ requirements.
In late lambing flocks, ewe condition often declines over autumn. The good news is that the effects of any loss of ewe condition in early pregnancy on progeny birth weight, fibre diameter and fleece weight can be overcome by re-gaining any condition lost by lambing. This is achievable on good green pasture after the break of season. In early lambing flocks, the cost of feeding supplements to achieve condition gain are very high, so it is recommended that early lambing flocks achieve good condition at joining and are maintained through until lambing. For more details on optimum nutritional profiles for different lambing times and pasture systems please visit the
regional guidelines pages at lifetimewool.
Figure 2. Optimum condition score profile for ewes lambing in late winter (Source: Lifetimewool).
It is recommended that ewes are assessed for body condition at day 90 (around scanning time) and again 1 month pre-lambing at vaccination time. Worm control and flystrike control should be done at this time so that it is in place before lambs are on the ground.
For ewes on green pasture in late pregnancy it is important for the pasture to have density and height to ensure an adequate intake. Feed on Offer (FOO) or Herbage Mass (HM) are both measures of pasture availability that are commonly used in Australia. Herbage mass assumes an amount of pasture is unavailable below a certain height, whereas FOO includes all pasture above ground level. Usually FOO is about 300 kgs more than HM for the same pasture. Both are measured as kilograms of dry matter per hectare (kg DM/Ha). (
Details on the different methods).
The targets will vary on the type and composition of the pasture (for more details see the FOO photo gallery at
www.lifetimewool.com.au/pastures.aspx ), but general amounts are provided here
- HM green - 700 singles and 900 twins in late pregnancy increasing to 1000 and 1200 by lambing (eg. using MLA pasture stick)
- FOO green-1000 increasing to 1200 for single ewes & 1500 for twins by lambing (mixed perennial pastures)
- FOO green - 900 increasing to 1500 FOO by lambing (annual clover/grass pastures)
Pasture targets for lambing on dry feed require knowledge of feed quality and quantity and careful monitoring of ground cover to ensure energy requirements of the ewe are being met as well as minimising the risk of erosion. If pasture targets are not being met then appropriate supplements will be needed and should be a balance of energy (>12 MJ) and protein (~12% protein). Any cereal grain supplement should have finely ground limestone added.
Management at lambing
Move ewes into lambing paddocks no later than one week before lambing is due to start.
Many recommend lambing mob sizes of;
- 400-500 ewes for single bearers
- 250 ewes for twin bearers
A lambing paddock should provide shelter, privacy, adequate feed and water, freedom from predators and minimal disturbance. It takes 6 hours for a ewe to recognise her lamb and lambs take twice as long to recognise their mother so it is important to provide an environment where the ewe will stay at the birth site for a long as possible. Merino ewes tend not to recognise twins and if the lamb is abandoned within 6 hours after birth there is no chance of survival.
Ewe Mortality:
Ewe mortality is an important issue when condition score falls below 2.0 during late pregnancy or at lambing. Maintaining adequate ewe condition is especially important where there is likely to be poor weather conditions and/or low pasture feed availability at lambing.
Any individual ewe whose condition score is less than 2.0 prior to lambing should be managed separately and have increased access to good feed. Twinning ewes are more likely to be in danger than single bearing ewes, with at least 2-3% higher mortalities for the same score. Single bearing ewes in particularly good condition maybe at increased risk of having lambing difficulties (dystocia).
Figure 3. Ewe mortality at lambing in a range of environments.
CJ Hawkins Homestead, University of New England, Armidale NSW 2351