Effects of Different Dietary Energy and Rumen-Degradable Protein Levels on Rumen Fermentation, Nutrients Apparent Digestibility and Blood Biochemical Constituents of Chinese Crossbred Yellow Bulls

The experiment was conducted to evaluate the effects of two dietary energy levels (TDN: 70 and 76% DM) and two rumen-degradable protein levels (RDP: 7.7 and 9.4% DM) on rumen fermentation, nutrients apparent digestibility and blood biochemical constituents of Chinese crossbred yellow bulls. Four ruminallyfistulated Charolais×Nan yang yellow bulls, about 540±23kg live weight, were randomly assigned to a 2×2 factorial arrangement in a 4×4 Latin Square design to receive four dietary treatments. The treatments were as follows: low energy and high protein (LEHP; TDN: 70%, RDP: 9.4%), high energy and high protein (HEHP; TDN: 76%, RDP: 9.4%), low energy and low protein (LELP; TDN: 70%, RDP: 7.7%) and high energy and low protein (HELP; TDN: 76%, RDP: 7.7%). Ruminal pH and total volatile fatty acids were not different among treatments. The acetate concentration was lower and propionate concentration was greater (P 0.01) for bulls fed HE diet compared with LE diet. The higher ammonia nitrogen (NH3–N) concentration was found for bulls fed HP diet compared to bulls fed LP diet (P 0.01). Total apparent digestibility of dry matter (DM), crude protein (CP), organic matter (OM) and N utilization were greater for bulls fed HE vs LE diet (P 0.05). Bulls fed HP diet had increased N retention than those fed LP diet (P 0.05). Blood biochemical constituents were not different among all dietary treatments, except plasma urea nitrogen (PUN) which was higher in HP dietary treatment (P 0.05). These findings suggest that high energy and high protein (energy: 76%, RDP: 9.4%) treatment is the best for high performance of yellow bulls without affecting their health.