Concentrate finishing systems for store lambs often involves a dramatic change in the basal diet as lambs are moved from being managed on, e.g. grass and / or roots to concentrates. If this is done too quickly there is a risk of digestive disturbances leading to acidosis and secondary infections. Hence, the selection of the carbohydrate balance between starch and digestible fibre is crucial as ruminants fed high levels of starch-based concentrates can develop sub-clinical acidosis and liver abscess, leading to decreased voluntary food intake and daily live weight gain (DLWG). The aim of this study was to evaluate two concentrate formulations for effective growth for finishing of Swaledale lambs, one concentrate being starch biased the other digestible fibre biased.