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Sheep Matters_Aug-Sept 17 (redesigned)

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Using BCS to plan ewe

Using BCS to plan ewe nutrition Ewe nutrition affects mating success. It is estimated that every missed pregnancy costs around £1.70 per ewe. Ewes that are on a wellmanaged programme of nutrition will be fit for mating and should result in a positive lamb output. Good nutrition is fundamental to ewe performance with requirements varying throughout the year. Nutrition not only has immediate impacts but also influences long-term ewe productivity (1). The objectives of a strategy for ewe nutrition between production cycles are as follows: • ●Achieve the correct BCS for successful mating; • ●Optimise conception rates and maximise embryo survival; • ●Reduce lambing period by aiming for 75% of ewes to hold at the first cycle; • ●Increase vitality of lambs produced by ‘immature’ ewes; and • ●Improve flock profitability. The importance of Body condition scoring (BCS) Body condition influences fertility, lamb performance and resilience to disease. Weaning should have taken place to allow enough time for the ewe to recover condition. General guidance is that a BCS of 3.5 for a typical 70kg lowland breed ewe and a BCS of 2.5 for a typical 50kg hill breed ewe should be achieved prior to mating (1). Because it typically takes 6-8 weeks to gain one BCS unit on a high quality grass diet, weaning should have been completed at least 10 weeks before mating, although this period may be significantly longer in hill breeds and for ewes who are particularly compromised and therefore require early weaning. ‘Increasing body condition score from 2.5 to 3.5 can increase scanning percentage by up to 20-40% Ewe lambs (hoggets) should be at 60% of mature weight and ewe shearlings should achieve 80% mature weight prior to mating (2). For prolific breeds such as Llyen and Aberdale research suggests that the BCS should be lower at between 2.5 and 3. A key hormone which supports the development of the foetus is progesterone. This hormone is produced by the corpus luteum (remnants of the follicle from which the egg is released from the ovaries). While highly prolific ewes naturally ovulate more eggs than traditional breeds, each follicle has less capacity to release progesterone. Heavy feeding will encourage more eggs to be produced than normal but will also limit the amount of progesterone that is released to support foetal development (2). Calculate nutritional requirements Following weaning, best practice will have resulted in the sorting of ewes into three groups based on BCS (fat, fit and thin). The nutritional requirements for each group should be determined on the basis that putting on one unit of condition adds between 10%-13% of liveweight. Feeding groups should be re-assessed every 2-3 weeks. Grazing management is critical because grass is the most economic source of nutrition and provides over 90% of the energy and protein requirements in most sheep systems. The best grazing 14 AUGUST & SEPTEMBER 2017

should be provided to ewes with the lowest BCS. Supplements should only be provided if flock demand is not met by grass supply. For a typical March lambing flock, supply is usually sufficient in September and October but a deficit develops through November (1). Optimum daily grass growth is achieved when pasture cover is between 2000 – 2500 kg DM/ha. - equivalent to a sword height of 8-12cm. To achieve the high intake needed for ewes to reach mating BCS they should be grazed on high quality, leafy pasture with a sword height of 6-8cm (2). If swords are too short, affected by drought, or if weather conditions disrupt grazing then additional feeding may be required. AFRC and AHDB provides guidance on determining requirements (1,3). To flush or not to flush? Nutrition has a long-term impact on ovulation rate. In addition, different breeds respond to flushing differently. The rumen is significantly affected by changes in feed type and quantity. To maintain rumen function sudden changes in diet must be avoided (1). ‘It is sensible to consider whether flushing is necessary or not’ Q 2017 AUGUST & SEPTEMBER 15

Sheep Matters - August/ September 2017