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Body Condition Score Key to Weight of Lambs Weaned

21 October 2014
EBLEX

UK - Ewe body condition score and weight at mating has a carryover effect on subsequent weaning weights, according to the early findings of a pilot project on sheep Key Performance Indicators (KPIs) commissioned by EBLEX.

Ewe weight at both weaning and mating in studies in 2012 had an influence on litter size at scanning in January 2013. Higher scanning percentages resulted from the heavier ewes within a breed at weaning.

Early results suggest ewes that were heavier or had a higher body condition score (BCS) at the target of 3.5 for lowland ewes at tupping went on to rear more lambs and produce a higher overall weaning weight of lamb per ewe than ewes in poorer condition (too thin and too fat).

There may also be some benefit from weight gain between weaning and tupping for lamb performance the following year. Managing ewes so they have the opportunity to gain condition before tupping, when they have mobilised some condition during lactation, may therefore see more kilograms of lamb weaned.

The target BCS for ewes at tupping on an individual farm will depend on ewe breed, the lambing percentage and farm terrain, but would typically be approximately:

  • 3.5 for lowland flocks
  • 3 for upland flocks
  • 2.5 for hill flocks

However, there are some opportunities to adjust BCS during the autumn. It may be possible for ewes to gain 0.5 BCS during flushing and tupping, when enough feed is available. Supplementary feeding, using concentrates, whole oats or barley, or high-energy supplements, such as feed buckets, could be considered to boost thin ewes which are below their target. When supplements are given, they must be continued throughout the tupping period and for three weeks after removing rams to avoid sudden dietary changes at a crucial time.

It needs to be remembered that implantation doesn’t occur for three weeks after fertilisation so stress, including dietary changes, moving or transporting ewes, needs to be minimised to reduce the risk of embryos being lost before they are attached.
If ewes are more than 0.5 BCS over target in the lead up to tupping, do not starve them, but do not allow them to gain any more condition. Flushing ewes that are BCS 4 or over will have no impact on scanning percentage, as over-fit ewes have a higher rate of embryo death, despite higher ovulation rates.

Once ewes are pregnant, the aim should be to maintain BCS. If ewes are on target or over target, a small amount of condition (0.5 BCS) can be lost during mid-pregnancy without affecting foetal growth. Ewes below target BCS should be separated and managed to gain some condition (0.5 BCS) during the second and third months. It is crucial that they do not lose any more condition.

Scanning offers one of the last opportunities to separate ewes based on scanning results and BCS. At this stage, the target BCS would typically be:

  • 3 for lowland flocks
  • 2.5 for upland flocks
  • 2 for hill flocks

 

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