Adaptive changes in microbial synthesis and nitrogen balance with progressing dietary feeding periods in sheep fed diets differing in their ruminal degradation synchronicity between nitrogen and organic matter

Abstract

ABSTRACTTwo diets differing in their degrees of ruminal degradation synchronicity between nitrogen (N) and organic matter (OM) were fed to six adult rams at a maintenance level for three months in a two‐way layout design combining a randomized block design. Adaptive changes in microbial N (MBN) supply and N balance were investigated for both diets. The in situ rumen degradation parameters of OM and N were determined for four feeds and subsequently were used to formulate the two diets to have different ruminal degradation synchronicity and to be identical with metabolizable energy (ME), metabolizable protein (MP) and ruminally degradable N concentrations. The animals were divided into two groups and fed asynchronous (ASYNC) or synchronous (SYNC) diet, respectively. On days 30, 60 and 90 of each feeding period, a five‐day metabolism trial was carried out. Animals consumed their diets thoroughly and did not show marked body weight change during the observation. The apparent digestibility of OM and N did not differ significantly between the diets throughout the periods. The MBN supply was significantly greater for ASYNC than that for SYNC (P < 0.01) and was greater on days 60 and 90 than that on day 30 (P < 0.05). Neither diets nor periods had a significant effect on the efficiency of MBN synthesis. There was a significant period effect on N retention (P < 0.05) together with tendency of diet × period interactions (P = 0.1). There was no significant dietary effect. An improvement in N retention with advancing feeding period was observed for both diets. The plasma urea concentration decreased with feeding period (P < 0.01) and there was a concomitant decrease in urinary N excretion. Plasma glucose concentration tended to increase (P = 0.07). The results suggest that lengthening feeding duration from 30 days might have caused ameliorative changes in the utilization of ME and MP, and may have improved microbe synthesis irrespective of the degradation synchronicity.