Growth, body composition, and visceral organ mass and metabolism in lambs during and after metabolizable protein or net energy restrictions.

Three trials were conducted to assess effects of metabolizable protein and NE deficiencies on changes in body composition, organ mass and metabolism, and animal growth performance during restriction and realimentation. Growth of lambs was restricted to achieve no change in BW for periods of 5 to 6 wk by limiting intake of metabolizable protein or NE. In Trial 1, changes in body composition and visceral organ mass and metabolism during restriction were compared to unrestricted controls using 36 lambs. Trial 2 was designed to investigate changes in growth, body composition, and visceral organs during restriction and realimentation periods using 44 lambs. Trial 3 was limited to evaluation of differences in performance and carcass characteristics of previously restricted and unrestricted ram lambs (15 total). Results of Trial 1 indicated that liver weights were decreased with nutrient restrictions. Body protein mass was conserved in energy-restricted (ER) lambs and lost in protein-restricted (PR) lambs. Fat was mobilized at similar rates for PR and ER lambs. In Trial 2, liver and intestinal weights, as well as in vitro oxygen consumption by liver slices, were decreased with nutrient restrictions. The reductions persisted after 2 wk of realimentation, yet no compensatory growth was observed. Feed intakes were increased gradually during the first 2 wk of realimentation. Composition of gain during the realimentation period was similar to that of unrestricted lambs. In Trial 3, neither gain nor feed efficiency during realimentation was enhanced as a result of previous nutrient deficiencies. Absence of compensatory growth in Trial 3 is possibly attributable to differences in gastrointestinal fill. Lambs subjected to short-term PR and ER seem to have similar recuperative capacity.