Effect of Dietary Crude Protein Level on UT-B Expression and Nitrogen Efficiency in Growing Baluchi Male Lambs Fed Low or High Concentrate Diets

An experiment was carried out to evaluate how interactions between forage to concentrate ratio and dietary crude protein level may alter nitrogen efficiency and UT-B expression in growing Baluchi male lambs. Four Baluchi male lambs [30 ± 2 kg BW] were used in a 4 × 4 latin square design with 28-d periods and a 2 × 2 factorial arrangement of dietary treatments. The treatments fed forage: concentrate [FC; DM basis] ratios of 45:55 low concentrate (LC) or 25:75 high concentrate (HC) with dietary levels of CP of 14 low protein (LP) or 18% high protein (HP) [CP, DM basis]. Dry matter intake increased as dietary concentrate level in-creased. Treatments, dietary CP content and F: C ratio had significant effect on CP intake. Increasing die-tary N content of the diet increased dry matter (DM), crude protein (CP) and organic matter (OM) digesti-bility. Forage to concentrate ratio had a significant effect on neutral detergent fiber (NDF) and OM digesti-bility. Treatments had significant effect on the CP, NDF and OM digestibility. There were an interaction between dietary CP content and F: C ratio on the ruminal pH, NH3-N concentration, individual volatile fatty acids (VFA) concentration, acetate: propionate ratio and BUN concentration. Except ruminal pH, all ru-minal fermentation and blood metabolite factors were affected by both dietary CP content and F: C ratio in trial. Treatments had significant influence on the NI (g/d) and urinary N excretion (g/d) (% of N intake). Also, both dietary CP content and F: C ratio had significant effect on NI. The lambs consume high crude protein treatments tended to have greater urinary N excretion (g/d) than those consume low crude protein treatments. The F: C ratio had a significant effect on urinary N excretion (g/d). Approximately 6.56 times more UT-B was expressed by the rumen ventral sac for lambs on the treatments contain 18% crude protein relative to those on the treatments contain 14% crude protein. In conclusion this study shows that changes in characteristic of the diet produce significant changes in UT-B urea transporter expression within the ovine rumen. Changing urea entry into the GIT via dietary regulation of UT-B could serve as important mechanism to maintenance of nitrogen balance and increase nitrogen efficiency in Baluchi growing lambs. Our findings suggest that the dietary regulation of urea transporters plays a major role in altering urea entry into the gastrointestinal tract.