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Sunday 26 March 2017

Keep a close eye on ewe pre-lambing feed needs

Dr Tommy Boland

Our ewes were scanned two weeks ago and it's fair to say we were disappointed with the results. In the mature ewes, conception rate to first service was 80pc and for the ewe lambs it stood at 60pc.



The overall litter size of the mature ewes stands at 1.7. This is about 0.3-0.4 below what we would target. When we look at the litter size of the ewes scanned as in-lamb it looks a bit more respectable at 1.88.

This figure, however, excludes the 25 barren ewes. Out of a flock of 300 ewes, 25 barren ones is too many. This is a problem which has reared its head now for two years in a row, and we had previously not experienced it. It appears to be linked to the phenomenon of deep-end anoestrus which is associated with laprascopic AI on occasion. In terms of the ewe lambs, the overall litter size stands at 1.25 and litter size of lambs scanned pregnant is 1.4 lambs per ewe. In terms of what we would expect our weaning litter size to be, you could project it to be about 0.2 below the scanned litter size. Ewes were in good body condition at mating and have increased slightly in body condition to a score of 3.5 (ewe lambs 3.1). Average ewe weight (excluding last year's ewe lambs) is 83kg and the ewe lambs bred in 2010 (this year's second lambers) averaged 78kg.

At this stage, the figures can't be increased and we need to focus on feeding the ewes for the next six weeks. Good quality grass silage will meet the energy requirements of the ewe type we have, up to the last six weeks of pregnancy. A ewe will consume about 1kg of silage dry matter in late pregnancy, although this will drop in the last two weeks of pregnancy. Silage intake capacity does not change that much between single and twin-bearing ewes, but ewes carrying triplets will consume about 15pc less silage.

Energy demand rapidly increases in the last six to seven weeks of pregnancy and protein requirements in the last two to three weeks. A ewe carrying two lambs with an expected birth weight of 5kg each will see her energy requirements almost double from seven weeks pre-lambing to lambing time. This increase in energy demand needs to be met by increased concentrate intake, and the level of concentrates required is increased as forage quality decreases. Care needs to be taken with the pattern of concentrate feeding. Once the level goes above 500g/day, consider splitting the feed. This will reduce the risk of digestive problems such as acidosis and allow the ewe to make use of the silage she is consuming.

In terms of protein requirements, quantity and quality of protein become important in the final three weeks of pregnancy. The ewe in mid-pregnancy requires only about 100g of crude protein/day. The requirement increases up to about 200g at the point of lambing for a medium-sized animal carrying twins. At Lyons, we have got a response in colostrum production up to about 180-190g of crude protein/ewe/day, but not at any higher values.

Up to the last three weeks, if you are feeding a grass or grass silage diet, and energy requirements are being met, you are most likely to also meet your ewes' protein requirements. After this point you need to feed a source of protein that contains some rumen by-pass protein. This protein will escape digestion in the rumen but will be broken down further along the digestive tract. About 25pc of the protein intake should escape rumen digestion in late pregnancy. Traditionally, fishmeal was an excellent source of protein to meet this requirement, but as that is not permitted in ruminant diets, soya bean is the best alternative.

Unfortunately, the requirements are more complicated than outlined here. If energy is deficient in late pregnancy, then the requirement for supplementary protein is increased and occurs earlier. All too often we refer to protein requirements as the percentage of crude protein in the compound feed. This should not be looked at in isolation from the quality and quantity of roughage consumed. The poorer the roughage, the greater the need for a high-protein, high-quality supplement.


Dr Tommy Boland is a lecturer in sheep production at Lyons Research Farm, UCD. Email: tommy.boland@ucd.ie

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