Energy and Nitrogen Metabolism in Lambs During Feed Restriction and Realimentation

Eighteen crossbred Swifter (Flemish ♀ X Texel ♂) male lambs, born in March 1997 and weaned at the age of approximately 3 months, were used to quantify effects of feed quality restriction and realimentation on changes in energy and nitrogen metabolism. The ration consisted of grass straw (17 MJ of GE and 46 g CP per kg DM) on an ad libitum basis and 35 g.kgd mixed concentrates (16.5 MJ of GE and 173 g CP per kg DM). At the age of approximately 3.5 months, the animals were randomly divided into six blocks, based on live weight, according to a randomized complete block design. Within each block, the animals were randomly assigned to two restricted treatments (R1 and R2) and a control treatment. Treatments R1 and R2 were subjected to feed quality restriction by withholding concentrate for 3 and 4.5 months, respectively. A modified linear model was developed to study the effects of restriction and realimentation. The comparison between treatments was made by analyzing the data of R1 and R2 animals as deviations from the control animal in each block. During the restriction period, restricted animals lost weight and showed a negative EB and NB, whereas their intake from low-quality roughage significantly (P < 0.001) increased. After realimentation, the R1 and R2 animals grew significantly (P < 0.001) faster than the C animals. The realimented animals persisted in ingesting more (P < 0.001) low-quality roughage and their EB and NB were greater (P < 0.001) than those of C animals. The R2 animals needed a longer period of realimentation because of a longer period of restriction. The expression of compensatory growth was mainly related to a sustained higher (P < 0.001) grass straw (low-quality roughage) intake during realimentation periods, and greater (P < 0.001) efficiency of metabolizable energy intake. The maintenance requirement of realimented animals was lower (P < 0.001) only during the initial stages of realimentation compared with controls.