Effect of ruminal glucose infusion on dry matter intake, urinary nitrogen composition, and serum metabolite and hormone profiles in ewes

Twelve 18-mo-old Debouillet ewes were used to determine the effect of rumin al glucose infusion on DMI, on urinary ammonium (NH4+) and urea N (UUN) con centrations, and on serum metabolite and hormone profiles. Ewes were limit- fed a 90% concentrate diet for 30 d, stratified by BW into three groups (av erage BW = 82.6 +/- 1.1 kg), and assigned randomly to receive 0, 5, or 10 g of glucose/kg of BW via esophageal intubation. Urine was collected hourly for 12 h and blood (jugular venipuncture) at 30-min intervals for 12 h. Aft er 12 h, ewes were housed individually, allowed free access to the diet, an d DMI was recorded for 5 d. Venous blood pH averaged 7.49, 7.48, and 7.48 a t 0 h and decreased (linear [L], P < .01) at 12 h (7.41, 7.36, and 7.26) wi th increasing glucose. Serum glucose increased (L, P = .06) at 3 and 6 h. S erum L(+)-lactate increased (L, P = .08) at 3, 6, and 9 h, whereas serum D( -)-lactate increased linearly (P = .09) at 6 and 9 h and quadratically (P < .10) at 12 h. After the glucose challenge, DMI decreased (L, P < .05). Uri nary pH and NH4+ were not influenced by glucose infusion; however, UUN incr eased at 3 (quadratic [Q], P < .05), 4, 5, 6 (L, P = .03), and 7 h (Q, P < .05) and decreased at II and 12 h (L, P = .09). As glucose infusion increas ed, serum creatinine increased at 9 (L, P < .01) and 12 h (Q, P = .02). Gen erally, serum Na and P increased (P = .09), whereas K decreased (P < .05), with glucose infusion. Lactate dehydrogenase activity increased with glucos e infusion (Q, P < .10) at 3, 6, 9, and 12 h. Increasing glucose infusion i ncreased serum globulin (Q, P = .06), albumin, and total protein (L, P = .0 8). Serum prolactin and vasopressin were not influenced (P = .22) by glucos e infusion. Serum insulin and aldosterone increased quadratically (P = .08) , whereas serum growth hormone decreased linearly (P = .08) as a result of increasing glucose infusion. Results suggest that UUN, serum insulin, aldos terone, and several serum constituents may serve as markers of organic acid load in ruminants fed high-concentrate diets.