Energy and Nitrogen Metabolism in Lambs During Feed Restriction and Realimentation

Eighteen crossbred Swifter (Flemish ♀ X Texel ♂) male lambs, born in March ۱۹۹۷ and weaned at the age of approximately ۳ 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 (۱۷ MJ of GE and ۴۶ g CP per kg DM) on an ad libitum basis and ۳۵ g.kg-.۷۵d-۱ mixed concentrates (۱۶.۵ MJ of GE and ۱۷۳ g CP per kg DM). At the age of approximately ۳.۵ 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 (R۱ and R۲) and a control treatment. Treatments R۱ and R۲ were subjected to feed quality restriction by withhold-ing concentrate for ۳ and ۴.۵ months, respectively. A modified linear model was devel-oped to study the effects of restriction and realimentation. The comparison between treatments was made by analyzing the data of R۱ and R۲ 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 sig-nificantly (P < ۰.۰۰۱) increased. After realimentation, the R۱ and R۲ animals grew signifi-cantly (P < ۰.۰۰۱) faster than the C animals. The realimented animals persisted in ingest-ing more (P < ۰.۰۰۱) low-quality roughage and their EB and NB were greater (P < ۰.۰۰۱) than those of C animals. The R۲ animals needed a longer period of realimentation be-cause of a longer period of restriction. The expression of compensatory growth was mainly related to a sustained higher (P < ۰.۰۰۱) grass straw (low-quality roughage) intake during realimentation periods, and greater (P < ۰.۰۰۱) efficiency of metabolizable energy intake. The maintenance requirement of realimented animals was lower (P < ۰.۰۰۱) only during the initial stages of realimentation compared with controls.

کلیدواژه ها:

Energy metabolism ، Feed restriction ، Metabolizability ، Nitrogen metabolism ، Realimentation