The aim of nutritional management pre conception is to have the ewe at optimum condition at joining to facilitate high fertility and a successful conception. The ewe should be on a level or slightly rising plane of nutrition from three weeks pre-joining to four weeks post joining. Body condition score of the ewe at joining impacts on subsequent litter size and weaning rate (lambs reared per ewe joined) with each one unit increase in condition score (within the range 2.5 to 4) at joining increasing litter size by 0.13. This increase in litter size subsequently increases weaning rate by 0.1 lambs per ewe put to the ram. joining ewes at a condition score of less than 2.5 increases the risk of barrenness, consequently, further reducing weaning rate.
BCS 1 BCS 3 BCS 5
Within the condition score range of 2.5 to 4.0 for many lowland breed types, each 1 unit increase in condition score is equivalent to an increase of approximately 12 kg in live weight or approximately 15% of live weight. In general, ewes fed high quality grass swards can gain approximately 1 kg live weight per week so it is important to allow sufficient time to improve condition score. To ensure the correct body condition at joining (3.5 – 4) the ewes need to be body condition scored at weaning and again at least 6 weeks pre mating. Thin ewes will require preferential treatment with access to high quality pasture or supplemented with concentrates to improve condition score pre mating.
In the past prior to joining, ewes were “flushed” which is the practice of reducing condition post weaning by tight grazing, and then raising the plane of nutrition for about three weeks prior to joining so that they would be improving in live weight and body condition at mating. However, if ewes are in good condition after weaning they should not be deliberately “slimmed down” with the intention of improving condition prior to mating. This practice would be an inefficient use of energy intake by the ewe.
Additional information: https://www.teagasc.ie/media/website/publications/2010/EweBodyConditionImpactsWeaningRate.pdf