Full-feeding versus overnight fasting for assessing growth potential of lambs

Abstract

Two experiments were performed in order to determine the best method for evaluation of weight-gaining ability of lambs. Lambs on unrestricted access to feed and water (full fed) gained 2–3% of live weight on the following day while lambs deprived of feed and water (fasted) overnight gained 0–3%. However, full fed lambs lost 5–10% of live weight when fasted overnight, or gained 7–10% if full fed at night. In 38 to 43% of the lambs fasted overnight, weights measured at successive weigh days were identical, a higher proportion than in lambs subjected to other treatments. Estimates of intra-class correlations between weights on successive days in lambs fasted overnight prior to weighing, or full fed until weighing, ranged from −8 to 0%. Corresponding estimates for lambs fasted overnight followed by full feeding, or vice versa, were highly variable, due to differences in weight of gastro-intestinal and urinary tract (‘fill’) contents and ranged from 8 to 60%. There appears to be no justification for weighing on successive days when a single accurate weighing equals the average weight. It was concluded that overnight withdrawal of feed and water before weighing reduced significantly the variation in body weight associated with retention of feed and water, facilitating a more precise assessment of lamb's growth potential.