Thompsons’ Ruminant Nutritionist; Dr Ronald Annett
It’s hard to believe that this time last year, ewes were knee-deep in grass and ground conditions were perfect for running early lambers outside. But conditions are very different this year, and for all but the driest parts of the province, ewes due to lamb in the next six weeks should be housed as soon as possible, so they have time to settle on their winter diets before lambing commences. While it’s tempting to hold off on housing to save time and money, it could end up costing you more in the longer term. That’s because the energy balance of ewes (i.e. the difference between energy intake and requirements) during late pregnancy is a key driver of both lamb birth weight and milk supply. Avoiding a severe negative energy balance (NEB) is therefore critical to avoid lamb losses, and consequently maximize lamb output.
Avoiding negative energy
In most cases, ewes have made it through the winter in good body condition, helped by the earlier housing of cattle last year. In practice, it is almost impossible to avoid some loss of body condition in ewes prior to lambing, especially during the final two weeks of pregnancy, when nutritional demands for foetal growth and udder development are at their peak. If the loss of body reserves is carefully managed and doesn’t exceed 0.5 units of body condition, ewes should lamb down with good viable lambs and an adequate milk supply. Where the mobilization of body reserves is excessive, the risk of ewes developing pregnancy toxaemia (twin lamb disease), hypocalcaemia and other metabolic diseases increase significantly, and these can be fatal. However, sub-clinical levels of these diseases are often more important from a flock management perspective. For example, ewes lambing down with undersized lambs or insufficient colostrum are indicators that the NEB is excessive, and action is needed. The ewe’s maternal instincts may also be impaired by excessive NEB, affecting the ewe-lamb bonding process.The point in late pregnancy at which ewes encounter a negative energy balance is influenced by many factors, including ewe body weight, maturity, and expected litter size. From a nutritional perspective, forage intake and nutritional value are by far the most important factors. Triplet-bearing ewes fed a poor quality grass silage (10 MJ/kg DM) will enter NEB around 7-8 weeks off lambing, whereas single-bearing ewes fed nothing but high quality grass silage (11.5MJ ME/kg dry-matter) can remain in positive energy balance until two weeks off lambing. In this case, concentrate feeding for the usual 4-6 weeks before lambing increases the risk of oversized lambs and birthing difficulties. Forage analysis alongside pregnancy scanning are two of the most effective tools for managing energy balance and targeting concentrates at the ewes which need it most. Forage quality is often one of the greatest unknowns on many sheep farms, but it doesn’t have to be! Speak to your local Thompson Technical Sales Representative about getting your forage analysed and developing a feed plan tailored to your flock.
Concentrates are vitally important for managing energy balance pre-lambing, but feed management and presentation are equally important to success. The number one rule is to feed your ewes the best quality silage you have available, because silage intake in sheep is much more sensitive to nutritive value and fermentation characteristics than in cattle. Encouraging higher forage intakes will reduce both the severity and duration of the NEB and will have added benefits for rumen health. Preparations for lambing should therefore begin in May each year, with the aim of making the best quality silage possible, even if this means sacrificing yield.
Ewes can process and digest precision chop silage much easier than longer chop material, as a result, silage intakes can be as much as 30% higher when harvested by a precision-chop compared with a single or double-chop harvester or round baler. Precision-chop silage is thus preferable to bales, including those made by chopper balers, unless they can be further processed through a diet feeder to reduce chop length. Silage should always be kept as fresh as possible, and refusals removed before they become stale. Ewes will often select and consume the leafy components of a silage first, so if there is evidence of sorting at the feed barrier, remove the fibrous stemmy material rather than forcing ewes to eat it. With your silage analysis in-hand, it’s relatively easy to estimate energy intake from forage and adjust your feed rates accordingly. A twin-bearing ewe has an average daily energy requirement of 16 MJ/day over the last 6 weeks of pregnancy. Ewes fed a good quality grass silage should consume, on average, 1kg silage dry-matter per day over this period. So if the silage is supplying 11MJ/kg DM, ewes require 5MJ energy from concentrates to maintain energy balance, which is equivalent to a feed rate of approx. 450 g/day. However, if silage intake is 10% lower than expected, the energy deficit increases by 1.1MJ, so concentrate feed rates must be increased by 100 g/day to compensate.
When it comes to feeding concentrates, your daily feeding routine can also influence how much silage a ewe will consume. Offering concentrates in two meals rather than one can increase silage intakes in sheep by up to 25%, especially at high feed rates, and via TMR by a further 2-3%. As a rule, once the feeding level exceeds 0.5kg/ewe/day it is best to split the daily concentrate allowance into multiple feeds of no more than 0.5kg per feed, to reduce the risk of digestive upsets. Some producers feed concentrates at a flat rate throughout late pregnancy, to keep things simple, while others opt to increase the feed level on a weekly or fortnightly basis, in line with the growing energy requirements of ewes. In practice there is no evidence of a performance benefit from one approach versus the other, provided the total amount of concentrates fed is the same. However, one advantage with flat rate feeding is that, if poor quality silage is being fed, it avoids very high feed levels close to lambing.
Pen facilities should provide at least 400-450mm trough space per head to enable all ewes, including shy feeders, to get their fair share. Triplet-bearing or thin ewes (BCS <2.5) should be given some additional trough space (450-500 mm) to reduce the level of competition and stress. Overfeeding of thin ewes, to help them gain body condition, should cease at least 2 weeks before lambing because the ewe will partition energy mainly to her lambs during this period, rather than her body reserves, thus increasing the risk of foetal oversize. Overfat ewes (BCS >4) carrying multiple lambs are most at risk from pregnancy toxaemia as their silage intake will be depressed, but this risk can be managed by placing these ewes on a restricted-forage diet and feeding higher levels of concentrates. You should discuss this strategy with a nutritionist as it requires careful planning. The importance of clean drinking water should also not be overlooked when it comes to maximising energy intake. This is especially true when feeding hay, haylage or high levels of concentrates, as these dry feedstuffs will increase demand for water. Clean water should be available at all times, so remember to check flow rates and clean out water troughs on a weekly basis.
At Thompsons, our aim is to help ensure your lambing period runs as smoothly as possible. If you would like help or advice on feeding your ewes, contact your local Thompson Sales Representative or contact the mill on; 028 9035 1321.
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