title: Effect of degree of corn processing on urinary nitrogen composition, serum metabolite and insulin profiles, and performance by finishing steers.
abstract: Two experiments were conducted to determine the effect of degree of corn processing on urinary ammonia and urea N concentrations, serum metabolite and insulin concentrations, and feedlot performance of steers. Corn was processed by either dry rolling to .54 kg/L bulk density (DR42; 42 lb/bushel) or steam flaking to a bulk density of .36 or .26 kg/L (28 [SF28] and 20 [SF20] lb/bushel, respectively). Degrees of processing were selected to generate final products with 25, 50, or 75% enzymatically available starch. Available starch, expressed as a percentage of total starch for DR42, SF28, and SF20, averaged 24.5, 56.4, and 81.1% in Exp. 1 and 22.4, 60.1, and 80.1% in Exp. 2. In Exp. 1, 29 steers were housed in individual outdoor pens and 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 linearly (P < .03) as degree of processing increased, whereas water intake did not differ (P > .42) among treatments. Average daily gain, ADG:DMI, and hot carcass weight responded quadratically (P < .04) to an increasing degree of processing. Urinary ammonia and urea N concentrations were not influenced (P > .30) by degree of processing. Whole blood packed cell volume, serum glucose, creatinine, D(-)-lactate, L(+)-lactate, and lactate dehydrogenase activity did not differ (P > .15) among treatments. For insulin data, ME intake on the day of sample collection was evaluated as a covariate. On d 28, serum insulin (2.49, 2.95, and 1.80+/-.33 ng/mL) responded quadratically (P = .04) as degree of processing increased. 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 (18 pens; 12 steers/pen) and assigned to the same treatments used in Exp. 1. Daily DMI and carcass weight responded quadratically (P < .05), whereas ADG and ADG:DMI increased linearly (P < .04) with increasing degree of processing. Results suggest that the degree of corn processing influences serum insulin concentrations of feedlot steers; however, serum metabolites, urinary nitrogen composition, and carcass characteristics were generally not affected by degree of corn processing.
authors.affiliation: Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003-0003, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Brown
authors.forename: C R
authors.initials: CR
authors.lastname: Krehbiel
authors.forename: G C
authors.initials: GC
authors.lastname: Duff
authors.forename: M L
authors.initials: ML
authors.lastname: Galyean
authors.forename: D M
authors.initials: DM
authors.lastname: Hallford
authors.forename: D A
authors.initials: DA
authors.lastname: Walker
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000254:growth & development*; D005260:Female; D005511:Food Handling; D007328:Insulin / Q000097:blood*; D007774:Lactation; D008297:Male; D009584:Nitrogen / Q000097:blood* / Q000652:urine*; D011897:Random Allocation; D003313:Zea mays
chemical_list: D007328:Insulin; D009584:Nitrogen