Changes in maintenance energy requirements of mature sheep fed at different levels of feed intake at maintenance, during weight loss and realimentation

Abstract

Increased accuracy of estimating maintenance requirements of both mature and immature animals can be achieved by adjusting the estimate for changes in energy resulting from either tissue accretion or mobilisation that occur during the test period. The present study examined changes in maintenance requirements over time within individual mature sheep that were fed at either 100%,80% or 60% of maintenance for 15 weeks and then at 100% maintenance for a further 15 weeks. Animals were CAT-scanned to estimate total body fat, carcass muscle, non-fat visceral components(NFVC) and empty body weight the sum of fat,lean and bone depots in the body at regular intervals. Estimates for maintenance requirements, scaled for either empty body or carcass muscle weight, showed a decline during the early stages of weight loss and a subsequent increase towards the end of the restriction. As the changes in maintenance requirements were apparent after scaling for carcass muscle and empty body weight, it is likely that the changes reflected a decline in tissue requirements rather than a change in body composition. At the end of the realimentation period, there was no difference between the three treatment groups in maintenance requirements when scaled for carcass muscle weight. However, estimates scaled for empty body weight were higher in sheep previously fed at 60% of maintenance. Prior nutritional history may affect estimates of maintenance efficiency in mature animals if scaled for differences in empty body weight. Although scaling maintenance requirements for NFVC is conceptually important, errors in the estimate of NFVC inflated the variation in the scaled estimate, such that interpretation of the results was confounded.