Influence of the addition of urea to a low‐protein diet on plasma amino acids and other metabolites in growing bulls fed sugar beet silage

Abstract

The changes in the concentration of metabolites in the blood have been used for the evaluation of feeds for many years. This method has practical application in monogastric animals rather than in ruminants. The rate of protein and energy metabolism in the rumen influcnces the plasma cornFosition but it is not easy to establish a direct relationship between them, because many other factors (the rate of tissue metabolism, hormones) also influence the concentration of metabolites in the blood (MILLER 1973, BASSET 1974, BERGEN et al. 1973. ARMSTRONG and HUTTON (1974) and WILLIAMS and SMITH (1974) suggested however, that after obtaining a certain rhythm in the rumen processes, the digesta in the duodenum and the blood plasma contained a stabilized amino acid concentration.Since a relationship between the composition of rumen content and plasma could be found under some conditions we intended to investigate such relations by applying various feed rations. The present paper describes an experiment with bulls fed o n low-protein diet containing readily digestible carbohydrates, periodically supplemented with urea. The level of amino acids in the blood plasma and some metabolites in the blood and rumen content were estimated. Experimental procedureThe experiment was carried out on 8 bulls of an initial average body weight of 175 kg, divided into two equal groups: A and B and lasted 186 days. The animals of group A were fed o n sugar beet silage, urea-mineral concentrate and hay. The animals of group B during the first 102 days (first period) received the same ration but without urea. During the second period of 84 days the animals of group B received the same ration as group A. The composition of the rations is presented in Table 1.The rumen content and blood from all animals were analysed a t 15, 85 and 130 days of the experiment. The samples were collected before morning feeding U.S.