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Tuesday 26 September 2017

Optimum nutrition in ewes will reduce mortality rate

Optimum nutrition in ewes will reduce mortality rate
Optimum nutrition in ewes will reduce mortality rate
Tommy Boland

Tommy Boland

Many of the causes of lamb mortality can be avoided with appropriate nutrition of the ewe. Scanning and penning according to litter size, a good estimation of lambing date, forage analysis, adequate trough space and appropriate concentrate formulation and feeding are all important considerations.

Forage analysis will dictate how much meals are required. In general ewes will consume 1kg of grass silage DM in late pregnancy (average across last seven weeks), but this level will drop in the final two weeks of pregnancy. Issues such as low DM percentage, high ammonical nitrogen content, low DM digestibility, long chop length and low crude protein content will all reduce silage DM intake.

Any factor reducing the intake of silage or any forage offered will necessitate the earlier introduction of concentrate feeding and feeding of higher levels of concentrates.

Another issue with low forage quality is the time it spends in the rumen. Low dry matter digestibility leads to forage spending a long time in the rumen and produces a physical fill effect. This leads to pressure within the abdomen increase and is often implicated as a predisposing factor in prolapse. The risk is increased with small ewes, large litter size and excessive body condition score (BCS).

Formulation

Inappropriate formulation of concentrates (ie a lot of rapidly fermentable starch) and feeding large quantities of concentrates in a single feed (greater than 500gr per feed) can cause the pH in the rumen to fall. In mild cases this slows down the rate of forage digestion, increasing the filling effect of the forage. In severe cases acidosis develops which greatly reduces intake, predisposing conditions such as twin lamb disease and milk fever.

At high levels of cereal grain in the diet, inclusion of whole grains should be considered. These will not pass through the digestive system as is often feared. Rather they will slow down the rate of starch digestion in the rumen and help to maintain a healthy rumen. Other options include the inclusion of fibrous concentrate ingredients such as soya hulls or citrus pulp. However, overall energy content of the ration should not be compromised.

Other simple things to consider include ensuring all ewes are accessing the feed (trough space of 450-600mm per head), and no persistent underlying health conditions such as lameness or internal parasites.

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Twin lamb disease arises when the ewe's intake of energy is significantly below her energy requirements. The energy requirement of a twin bearing ewe will almost double during the last two months of pregnancy.

To make up any deficit in energy intake the ewe will mobilise fat reserves. When this situation becomes excessive the condition of twin lamb disease arises. It is similar to ketosis in dairy cows, but significantly more difficult to correct. Fat ewes, where intake is restricted due to high levels of internal fat and fat in the liver, and underfed ewes are particularly at risk. The symptoms of twin lamb disease include: depression; head pressing; apparent blindness; salivation and fine muscle tremors and will quickly advance to coma and death.

Many of the more serious symptoms associated with twin lamb disease are associated with a glucose deficiency, so glucose precursors such as propylene glycol are essential when attempting to treat. Treatment is often futile however.

If cases of twin lamb disease occur within a flock, it means many more ewes are in a high risk situation. Blood tests, in consultation with your veterinarian, can give a reasonable indication of whether a larger problem exists. Five to six ewes per group should be blood tested and the levels of beta-hydroxy butyrate assessed. If levels are above 0.8mmol per corrective action is required.

It ewes are managed correctly body fat mobilisation will be minimal during late pregnancy and this body fat can then be utilised for bridging the energy gap in early lactation. This is especially important for twin suckling ewes. In the first month of lactation the energy requirements of a twin suckling ewe will be 50pc higher than they were during the last week of pregnancy, while protein requirements will have doubled also.

Energy

Obviously, this places further stress on the animal. For a twin suckling ewe, milk production peaks between three to four weeks after she gives birth. Her intake does not peak until six to seven weeks after she gives birth. In the meantime she needs to mobilise body fat reserves to bridge the gap. Fat mobilisation at this stage is much less risky than during late pregnancy.

A 0.5 unit drop is BCS is equivalent to approximately 100MJ metabolisable energy. Spread over a seven-week period the daily energy supply coming from this level of body condition score change is equivalent to the energy content of 150g of barley.

Spring grass also has a high energy and high protein content and in many instances is sufficient, along with body reserve mobilisation, to meet the energy requirements of the ewe. Recent research by Frank Campion at Lyons Research Farm shows that low grass DM content has a significant negative impact on the intake of grazed grass, and supplementation is often merited in wet weather conditions.

Ensuring adequate milk production of the ewe is essential in supporting lamb growth rates. The lamb is entirely dependent on milk supply for the first five to six weeks of life. The lamb is also extremely efficient at converting milk in to live weight gain. In the young lamb one kg of live weight gain can be achieved from one kg of milk DM intake.

Data from Fiona McGovern's work at Lyons Research Farm show that live weight differences present at five weeks of age persist right up to weaning time and impact on how long it takes the lamb to reach target slaughter weight. Ewes that are poor milkers one year are likely to repeat that in subsequent years; so, where possible, they should be identified and culled from the flock.

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