Effects of ruminal glucose infusion and degree of grain processing on ruminant animal metabolism and performance

A series of experiments were conducted to determine the effects of ruminal glucose infusion and degree of grain processing on animal metabolism and performance. In Exp. 1, 12 ewes were limit-fed a 90% concentrate diet for 30 d 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 at 30-min intervals for 12 h. After 12 h, ewes were allowed free access to the diet, and DMI was recorded for 5 d. Blood pH decreased (linear [L], P < .01), whereas serum D(--)- and L(+)-lactate generally increased (P < .10) with increasing glucose. Serum glucose increased (L, P < .06) at 3 and 6 h, and creatinine increased at 9 (L, P < .01) and 12 h (quadratic [Q], P = .02). After the 12-h challenge, DMI decreased (L, P < .05). Urinary urea N generally peaked later and subsequently decreased as glucose infusion increased. Serum Na and P increased (P =.09), whereas K decreased ( P < .05). Increasing glucose infusion increased lactate dehydrogenase activity, globulin (Q, P < .10), albumin, and total protein (L, P = .08). Insulin and aldosterone increased (Q, P = .08), whereas growth hormone decreased (L, P = .08) as glucose infusion increased. In Exp. 2 and 3, corn was processed by either dry rolling to .54 kg/L bulk density or steam flaking to a bulk density of .36 or .26 kg/L. Degrees of processing were selected to generate products with 25, 50, or 75% enzymatically available starch. In Exp. 2, 29 steers were individually adapted to a 90% concentrate diet over 21 d. Whole blood and urine were collected before feeding and at 4 and 8 h after feeding on d 0, 7, 14, 21, 28, 84, and 140. Daily DMI decreased (L, P < .03), whereas ADG, ADG:DMI, and carcass weight responded quadratically (P < .04) to an increasing degree of processing. Packed cell volume and serum metabolites did not differ (P > .15) among degrees of processing. For insulin data, ME intake was evaluated as a covariate. On d 28 and 140, insulin responded quadratically (P < .03) as degree of processing increased. In Exp. 3, 216 steers (12 steers/pen) were blocked by BW and assigned to treatments used in Exp. 2. Dry matter intake decreased (Q, P < .05), Whereas ADG and ADG:DMI increased (L, P < .04) with an increasing degree of processing. Carcass characteristics did not differ (P = .08) among degrees of processing. Degree of processing seemed to influence serum insulin of steers, and insulin might serve as an indicator of metabolic acid load in ruminants fed high-concentrate diets. However, serum metabolites, urinary nitrogen composition, and carcass characteristics are generally not affected by the degree of corn processing.