Chapter 10.2 Manage your ewes to improve lamb survival
Background information
Poor survival of newborn lambs is a major source of lost productivity in breeding enterprises. All flocks, regardless of breed, enterprise type or reproductive rate can experience significant lamb losses. Most of these losses are associated with poor nutrition during pregnancy and management throughout the lambing period. By contrast, the number of ewes that fail to get in lamb is normally less than 10% of the mob.
Ewes that are pregnant and lactating produce about 20% less wool than a dry ewe. Ewes that lose a lamb at birth produce about 10% less wool than a dry ewe. This is in addition to the economic loss of the lamb.
At a glance
- Management of ewe nutrition during pregnancy increases lamb birth weight and survival.
- Ewes in condition score (CS) 3 or better at lambing are likely to wean more lambs.
- Manage twin-bearing ewes to be at least CS 3.3 at lambing.
- There is considerable economic loss when ewes get pregnant but fail to rear a lamb.
Introduction
Important management aspects of nutrition in the pregnant ewe include:
- At about 40 days after conception the placenta begins to grow and continues its rapid growth until about day 95. This is followed by accelerated foetal development from day 90 through to lambing at around day 150. These stages are shown in figure 10.3.
- Good nutrition in late pregnancy can overcome poor nutrition in early pregnancy. A CS change in ewes up to day 90 of pregnancy will change lamb birth weight by 0.3 kg and a CS change after day 90 will change birth weight by 0.5 kg. However, these CS changes can be difficult to achieve due to increasing nutritional demands on the ewe.
- The placenta and foetus represent a considerable mass in late pregnancy and feed quality needs to be high to enable sufficient intake of nutrients due to reduced stomach capacity. This is particularly the case in the last two weeks of pregnancy.
- Energy requirements for all ewes increases 100 days after the start of joining.
- Ewes can lose a small amount of weight (0.3 CS) in early pregnancy if high quality green pasture can be accumulated for grazing and weight gain in late pregnancy.
- When pasture conditions do not enable gains in late pregnancy, it is most profitable to maintain condition throughout pregnancy.
- Aim to maintain ewe condition around CS 3 or better in autumn lambing flocks.
- Improving ewe nutrition during late pregnancy will normally increase birth weight and lamb survival, as well as increasing wool production and fibre diameter in ewes.
- The birth weight of a lamb is determined by the following factors: sex, litter size, placental development, whether the ewe is a maiden or mature ewe, ewe condition, genetics, length of gestation and the timing, quality and quantity of pasture during pregnancy.
- Optimum birth weight for lamb survival is between 4.5 and 5.5 kg. Survival decreases sharply if lambs weigh less than 4 kg or more than 6 kg at birth.
- Research has shown that potential lifetime wool production of the progeny can be compromised by poor ewe nutrition during mid and late pregnancy. A decline of 1 condition score between joining and day 90 reduced progeny fleece weight by 190 g and increased fibre diameter by about 0.3 micron. The effects of changes in ewe condition score during late pregnancy were similar. The effects from both periods are cumulative.
- If ewes lose condition in early pregnancy and gain condition in late pregnancy, the effects are similar to maintaining condition throughout pregnancy.
- During pregnancy, foetal losses are relatively small. Toxicities that cause death of the foetus and infectious abortions can occur in some situations (see chapter 11.4 in MMFS Module 11 Healthy and Contented Sheep).
The challenge for management is to adopt strategies that are cost effective and wean more lambs.
Figure 10.3 Crucial reproduction milestones continue throughout the year and require adequate nutrition to optimise performance.
Source: Lifetimewool, adapted by AWI
Managing ewes during pregnancy
The most favourable nutritional strategy during pregnancy has the following key features (see tool 10.4):
- Ewes can manage a fall from CS 3 at joining to CS 2.7 at day 90 of pregnancy where high quality green pasture (high proportion of perennials, 30% legume, dead material 10% of total, digestibility of green around 75%) is available to allow a gain in weight back to CS 3 or better for late pregnancy. This weight gain can be difficult to achieve. Otherwise, maintain condition throughout pregnancy.
- One tactic may be to increase the pasture quantity available for late pregnancy by deferred grazing in early pregnancy. This will likely require additional supplementary feeding, but this occurs before ewe nutritional requirements increase significantly.
- Ewe CS needs to be at least score 3 at lambing to minimise mortality and optimise wool and meat production of progeny (tool 10.4).
- Single bearing ewes can be too fat at lambing and their condition should not exceed score 4 to minimise the risk of dystocia. Twin bearing ewes are rarely at risk of being too fat due to their higher nutritional demand.
- Pregnancy scanning your ewes is essential to identify dry, single and multiple pregnancies to allow you to allocate feed to meet the nutritional requirements of each cohort, leading to improved welfare and productivity outcomes. The nutritional requirements of a twin bearing ewe increase significantly in late pregnancy and lactation compared to that of a single bearing ewe, so prioritise feed for the multiple bearing ewes to improve lamb birth weight and lactation and minimise the risk of dystocia in your single bearing ewes.
- When CS cannot be increased by grazing management in late pregnancy, it is most profitable to maintain condition throughout pregnancy. If the ewes lose weight, supplementary feed.
- The most economically sound option to meeting CS targets is to match your sheep’s peak nutritional demands with pasture availability (see chapter 8.3 in MMFS Module 8 Turn Pasture into Product).
- In dry or drought years when the cost of supplementary feeding is very high, you may want to consider revising your feed budget and planning to slowly allow ewes to decrease to CS 2.5 but ensure that you feed to maintain or improve ewe condition in late pregnancy (see chapter 11.5 in MMFS Module 11 Healthy and Contented Sheep).
- Supplementary feeding in late pregnancy to increase liveweight is season and price dependent, and in some circumstances may not be of economic benefit but will likely still yield a welfare benefit. It can sometimes cause an increase in lamb birth weight to the point where dystocia (difficult births) may become a problem. Seek guidance from your animal health advisor to help in this decision-making process.
- Abortions and pasture toxicoses (such as campylobacter, toxoplasmosis, listeria, onion weed and perennial ryegrass toxicosis) occasionally cause major losses during pregnancy and at full term. Investigate any abnormal losses with your veterinarian or animal health advisor.
As a guide for spring lambing flocks on mixed perennial pastures:
- Single bearing ewes need feed on offer (FOO) of 800-900 kg high quality green dry matter (DM) per hectare and twin lambing ewes a FOO of 1,000-1,200 kg high quality green DM/ha during mid-pregnancy.
- On legume-based pastures, manage lambing paddocks to achieve a minimum FOO of 1,300 kg green DM/ha at the start of lambing.
- Twin bearing ewes need FOO of 1,800 kg green DM/ha on legume-based pastures.
- Aim to have twin bearing ewes in condition score 3.3 at lambing to optimise ewe and lamb survival.
- Use the pasture assessment Tools in tool 7.6 in MMFS Module 7 Grow More Pasture, see chapter 8.2 in MMFS Module 8 Turn Pasture into Product for more details of sheep nutritional requirements and signposts for further resources.
For information on clostridial diseases and parasite control during pregnancy see chapter 11.2 and chapter 11.3 in MMFS Module 11 Healthy and Contented Sheep.
Pregnancy scanning ewes
Pregnancy scanning, for either pregnancy status or litter size, is a valuable Tool for sheep enterprises. The data collected from pregnancy scanning can be used to increase profit and productivity through the sale of passenger ewes, effective feed allocation and targeted selection of replacement breeding stock.
The scale of benefits varies according to season, breed, region, the reproductive rate of the flock, the management of the scanned ewes and whether their number will affect the overall flock structure. Scanning for litter size increases profit by an average of $5.55 per ewe, while scanning for pregnancy status only returns an average of $2.65 per ewe. Scanning for litter size has been shown to be profitable across all scenarios. Tool 10.8 looks at the benefits of pregnancy scanning as a routine management practice.
The accuracy of pregnancy scanning is increased by:
- Scanning at the correct time. Based on the industry recommended five week joining period, pregnancy scanning should be conducted approximately 80-90 days after the rams go in with the ewes.
For joining periods longer than five weeks, scanning can be undertaken across a window of 70-100 days from rams in. However, accuracy will be highest between 80-90 days after the rams go in. - Keeping ewes off feed and water overnight prior to scanning.
- Having sufficient labour to keep ewes up to the scanning contractor. Depending on the individual setup, up to 3,000 ewes may be scanned in a day.
- Ensuring sheep yards are in good condition and able to ensure that any groups of ewes drafted apart based on pregnancy status can remain separated and be managed accordingly.
Timing of routine husbandry practices
As a general rule:
- It is not recommended to shear or crutch ewes within 4 weeks from the start of lambing due to the required time off feed and stress to the ewe, so plan to complete these operations before this window.
- Shearing increases feed requirements (even more so when shearing coincides with cold, wet and windy weather) making it difficult for pregnant ewes to meet their requirements.
- Being held off-pasture for shearing often results in condition loss in ewes and possibly higher supplementary feed requirements, especially in poor pasture growth seasons.
- If shearing happens to coincide with wet and windy weather there is a greater risk of metabolic problems and pregnancy toxaemia. Ewes in CS 3 or higher are better able to withstand the effects of cold weather after shearing.
- Carry out annual 6-in-1 booster vaccination of ewes between 4-6 weeks before lambing.
- In areas where ewes require a pre-lambing drench, this should be carried out at the same time as other pre-lambing husbandry operations.
- Trace element treatments may be given at this time or at shearing or crutching, but this should be discussed with your veterinarian or animal health advisor.
- Controlling fox predation is vitally important. Undertake fox control procedures well before lambing commences. See tool 5.7 in MMFS Module 5 Protect Your Farm’s Natural Assets.
- Reduce vertebrate pest (fox, wild dog and feral pig) numbers annually, but particularly prior to lambing to prevent predation and mismothering.
In the last 4 to 6 weeks of pregnancy there is a greater risk of toxaemia or metabolic syndromes such as hypocalcaemia. This can be offset by managing routine procedures to minimise stress on ewes and planning to complete these procedures at least four weeks before the start of lambing. Refer to chapter 11.5 in MMFS Module 11 Healthy and Contented Sheep and consult your veterinarian or animal health advisor for further information.
SIGNPOSTS
A ten-part video series centred around sheep reproduction. Tune in to hear a range of practical ways growers can influence sheep reproduction with the latest research and tools informed by the AWI-funded research and development outcomes. Episode 4 – Ewe condition scoring Episode 7 – Scanning to manage
Learn how to best manage foxes and wild dogs and deal with their impact on livestock businesses and communities.
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