Live weight and body composition associated with an increase in body condition score of mature ewes and the relationship to dietary energy requirements

•An extra unit of BCS corresponds to an increase of 7.74kg live weight in mature Romney-cross ewes.•The fat in the carcass increases as BCS increases up to 3.5 and then plateaus.•More energy is required to gain a unit of BCS when ewes are at a higher BCS.•Gaining body condition above a score of 3.5 is associated with an inefficient energy utilisation.