Effect of degree of corn processing on urinary nitrogen composition, serummetabolite and insulin profiles and performance by finishing steers

Two experiments were conducted to determine the effect of degree of corn pr ocessing on urinary ammonia and urea N concentrations, serum metabolite and insulin concentrations, and feedlot performance of steers. Corn was proces sed by either dry rolling to .54 kg/L bulk density (DR42; 42 Ib/bushel) or steam flaking to a bulk density of .36 or .26 kg/L (28 [SF28] and 20 [SF20] Ib/bushel, respectively). Degrees of processing were selected to generate final products with 25, 50, or 75% enzymatically available starch. Availabl e starch, expressed as a percentage of total starch for DR42, SF28, and SF2 0, averaged 24.5, 56.4, and 81.1% in Exp. 1 and 22.4, 60.1, and 80.1% in Ex p. 2. In Exp. 1, 29 steers were housed in individual outdoor pens and adapt ed to a 90% concentrate diet over 21 d. Whole blood and urine were collecte d before feeding and at 4 and 8 h after feeding on d 0, 7, 14, 21, 28, 84, and 140. Daily DMI decreased linearly (P < .03) as degree of processing inc reased, whereas water intake did not differ (P > .42) among treatments. Ave rage daily gain, ADG:DMI, and hot carcass weight responded quadratically (P < .04) to an increasing degree of processing. Urinary ammonia and urea N c oncentrations were not influenced (P > .30) by degree of processing. Whole blood packed cell volume, serum glucose, creatinine, D(-)-lactate, L(+)-lac tate, and lactate dehydrogenase activity did not differ (P > .15) among tre atments. For insulin data, ME intake on the day of sample collection was ev aluated as a covariate. On d 28, serum insulin (2.49, 2.95, and 1.80 +/- .3 3 ng/mL) responded quadratically (P = .04) as degree of processing increase d. Serum insulin did not differ (P = .52) on d 84, whereas insulin (5.77, 7 .51, and 4.12 +/- .98 ng/mL) responded quadratically (P = .02) on d 140. In Exp. 2, 216 steers were blocked by BW into two blocks 118 pens; 12 steers/ pen) and assigned to the same treatments used in Exp. 1. Daily DMI and carc ass weight responded quadratically (P < .05), whereas ADG and ADG:DMI incre ased linearly (P < .04) with increasing degree of processing. Results sugge st that the degree of corn processing influences serum insulin concentratio ns of feedlot steers; however, serum metabolites, urinary nitrogen composit ion, and carcass characteristics were generally not affected by degree of c orn processing.