Background information
Poor survival of newborn lambs is a major source of lost productivity in breeding enterprises where lambing percentages of 110–130% born can result in a marking percentage of 70–90%. Most of these losses are associated with poor nutrition during pregnancy. 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.
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.
- Good nutrition in late pregnancy can overcome poor nutrition in early pregnancy. A condition score change in ewes up to day 90 of pregnancy will change lamb birth weight by 0.3 kg and a condition score change after day 90 will change birth weight by 0.5 kg.
- The placenta and foetus represent a considerable mass in late pregnancy and feed quality needs to be high to enable sufficient intake of nutrients. This is particularly the case in the last two weeks of pregnancy.
- In normal seasons, spring lambing flocks require few additional nutrients through joining and early pregnancy until 100 days after the start of joining.
- Ewes can lose a small amount of weight (0.3 of condition score) if 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 keep ewe condition around score 3 in autumn lambing flocks.
- Supplementary feeding grain to day 100 of pregnancy to increase lamb survival has few economic benefits.
- Improving ewe nutrition during late pregnancy will normally increase birth weight and lamb survival, increase wool production in ewes but also increase fibre diameter.
- The birth weight of a lamb is determined by the following factors: sex, litter size, placental development, 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 6kg at birth.
- Recent research has shown that potential lifetime wool production of the progeny can be compromised by poor ewe nutrition during mid and late pregnancy. A 10kg drop in liveweight between joining and day 90 reduced progeny fleece weight by 190g and increased fibre diameter by about 0.3 micron. The effects of changes in ewe liveweight during late pregnancy were similar. The effects from both periods are cumulative.
- If ewes lose condition in one period and gain condition in the next, the effects are similar to maintaining condition throughout pregnancy. The effects are permanent for the progeny. During pregnancy, foetal losses are relatively small. Toxicities that cause death of the foetus and infectious abortions can occur in some situations. The challenge for management is to adopt strategies that are cost effective and wean more lambs.
Key decisions, critical actions and benchmarks
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 condition score 3 at joining to condition score 2.7 at day 90 of pregnancy where quality pasture is available to allow a gain in weight back to condition score 3 for late pregnancy. Otherwise, maintain condition throughout pregnancy.
- Ewe condition score needs to be at least score 3 at lambing to minimise mortality and optimise wool and meat production of progeny (tool 10.4).
- When condition score 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 least cost option to meeting condition score targets is to match the breeding cycle with pasture availability.
- In dry or drought years when the cost of supplementary feeding is very high, consider allowing ewes to fall to condition score 2.5, but maintain satisfactory wellbeing levels.
- Supplementary feeding in late pregnancy to maintain ewes in heavy condition or to increase liveweight is unlikely to be of economic benefit. It can cause an increase in lamb birth weight to the point where dystocia (difficult births) may become a problem.
- A tactic may be to increase the pasture quantity available for late pregnancy by deferred grazing in early pregnancy.
- Abortions and pasture toxicoses (such as vibrio abortion, onion weed and perennial rye grass toxicosis) occasionally cause major losses during pregnancy and at full term. Investigate any abnormal losses with your animal health adviser.
As a guide for spring lambing flocks:
- Single bearing ewes need Feed On Offer (FOO) of 700–900 kg green dry matter (DM)/ha and twin lambing ewes a FOO of 1,000–1,200 kg green DM/ha during mid-pregnancy. Note: Feed on Offer (FOO) is a measure of total pasture available to ground level.
- Manage lambing paddocks to achieve a minimum FOO of 1,200 kg green DM/ha at the start of lambing. A FOO of 1,500 kg green DM/ha is recommended with annual clover-based pastures.
- Twin bearing ewes need FOO of 1,800 kg green DM/ha on annual cloverbased pastures.
- Aim to have identified twin bearing ewes in condition score 3–3.3 at lambing to optimise survival.
- Use the pasture assessment tools in tool 7.6 in Grow More Pasture, PROGRAZE® courses and Lifetime Wool manuals.
For information on clostridial diseases and parasite control during pregnancy see procedures 11.2 and 11.3 in Healthy and Contented Sheep.
Pregnancy scanning ewes
The costs and benefits of pregnancy scanning ewes for litter size need to be carefully assessed and the appropriate ewe management procedures put in place to ensure best survival of twin born lambs to boost weaning rates. tool 10.7 looks at the pros and cons of pregnancy scanning as a routine management practice.
Timing of routine husbandry practices
As a general rule:
- Shearing ewes pre-lambing increases ewe feed requirements by 25–30% when shearing coincides with cold winter weather.
- In poor growth seasons, being held off-pasture for shearing, results in weight loss in ewes and possibly higher supplementary feed requirements.
- If shearing happens to coincide with wet weather there is also greater risk of metabolic problems and pregnancy toxaemia. Ewes in condition score 3 are more able to withstand the effects of cold weather after shearing.
- Crutching within four weeks of lambing is a lower risk strategy as ewes are less likely to be held off-pasture for extended periods.
- Carry out 6-in-1 vaccination of ewes between 2-6 weeks before lambing.
- In areas where ewes require a pre-lambing drench, make it close to lambing to gain the benefit.
- Trace element treatments may be given at this time or at shearing or crutching, but this should be discussed with your animal health adviser.
- Controlling fox predation is vitally important especially in twinning paddocks. Undertake fox control procedures before lambing commences.
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 off-set by managing routine procedures to minimise stress on ewes. Consult your animal health adviser for further information.
Signposts
Read
Planning for Profit – A practical guide to assist woolgrowers recover from
drought. Order your free copy from AWI by:
- Calling: 1800 070 099
- Downloading the document from: www.wool.com.au/Publications/Managing_drought/page__7134.aspx
Lifetime Wool Regional Guidelines - a series of guidelines and recommendations for managing ewe flocks throughout the year. Visit the Lifetime Wool website: www.lifetimewool.com.au/guidelines.aspx
