The effect of feeding sugar-beet silage and non-protein-N on rumen and blood metabolites in bulls.

1. The purpose of the experiments was to determine certain properties of the metabolism of nitrogen compounds and carbohydrates in the rumen and tissues of growing bulls which were given either a diet containing sugar-beet silage, a urea-mineral preparation and hay or a control diet with maize silage, ground barley and hay. Daily rations were given in two equal portions twice daily at 07.00 hours and 13.00 hours. The experiment lasted 182 d. 2. The experimental diet containing 0.54 g urea and 5.0 g saccharose/kg body-weight did not cause any symptoms of toxicity in the animals although there were large changes in the concentration of metabolites in the forestomach. The lowest pH (6.2–6.4) in the rumen of animals in the experimental group was observed 1.5 h after feeding. At the same time the highest level of lactic acid was observed, but the highest level of volatile fatty acids (VFA) was observed 3 h after feeding. Although there was a large increase in ammonia in the rumen contents (approximately 20 mmol/l at 1.5 h after feeding) an increase in the blood level of ammonia was not observed. 3. A lower level of acetic acid and higher level of butyric acid and valeric acid were observed in the rumen of animals given sugar-beet silage than in animals given maize silage and ground barley. Non-glucogenic ratio of VFA in the rumen of bulls after feeding the experimental diet was approximately 3.5 while on the control diet the value was considerably higher. 4. The causes of the low concentration of glucose in the blood and changes in other metabolites in the blood of experimental animals are discussed. 5. Average daily gains were higher ( P ≤ 0.05) in both groups of bulls given a diet containing sugar-beet silage and NPN (1087 and 1043 g/d) than with the control diet (887 g/d). Changes in the concentration of metabolites in the rumen contents and blood of sugar-beet-silage-fed bulls confirmed the possibility of effective addition of urea in an amount corresponding to 50% of the N content and also indicated good utilization of the energy in this diet.