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

The body condition score (BCS, on a 0-5 scale) for sheep was developed in the 1960s as a management tool to quickly assess body nutrient reserves. To quantify how live weight, chemical body composition and energy partitioning changes as BCS increases in mature ewes, a total of 28 mixed-age Romney-cross ewes were slaughtered at different BCS (1.5, 2.0, 2.5, 3.0, 3.5, 4.0 and 4.5) and the whole body chemical composition (skin, head, organs and carcass) was determined. The live weight increased linearly with BCS with an extra unit of BCS requiring 7.74 kg in live weight. The concentration of protein and inorganic matter in the whole body did not differ between BCS groups (P > 0.05). The concentration of water, fat and energy in the whole body increased as the BCS increased (P < 0.0001). As expected, the amount of energy required to gain one unit of BCS increased at a non-linear rate (P < 0.01), such that more energy was required at higher BCS to gain an additional unit of BCS. Increases in BCS above 3.5 are associated with increased heat energy loss and only a small proportion of energy is retained. The data indicated that from an energetic efficiency perspective there is little advantage in gaining BCS above a BCS of 3.5.