Comparative Effects of Whole, Ground, Dry-Rolled, and Steam-Flaked Corn on Digestion and Growth Performance in Feedlot Cattle

Professional Animal Scientist, Jun 2005 by Corona, L, Rodriguez, S, Ware, R A, Zinn, R A

Abstract

Two trials were conducted to evaluate four common methods of corn processing for cattle simultaneously. Experimental diets contained 75.3% com grain. Com processing treatments were 1) steam-flaked corn (SFC; density = 0.31 kg/L), 2) dry-rolled com (DRC; density = 0.58 kg/L), 3) ground corn (GC), and 4) whole com (WC). Treatment effects on feedlot perfonnance were evaluated in a 112-d finishing trial involving 120 crossbred yearling steers (311 kg). Cattle fed WC had less (7%; P

(Key Words: Corn, Processing, Cattle, Performance, Metabolism.)

Introduction

Several reviews of grain processing have been published (Hale, 1973; Theurer, 1986; Owens et al, 1997; Zinn et al., 2002). Most grain processing methods have, as their primary objective, improved starch digestibility. Steam-flaking consistently improved starch digestibility over that of whole corn (WC), dry-rolled corn (DRC), or ground corn (GC) (Matsushima and Mongomery, 1967; Lee et al., 1982; Zinn et al., 2002). Grinding or cracking improves starch digestion and BW gain efficiency over that of WC (Galyean et al., 1979; Turgeon et al., 1983). However, processing corn for maximum starch digestibility may not yield maximum BW gain efficiency (Owens et al., 1986; Secrist et al., 1995). For example, feeding finely GC depressed energy intake and growth performance (Secrist et al., 1996a). This effect was due to reduced ruminai pH and associated digestive dysfunctions. The objective of this study was to compare simultaneously four of the more common methods of corn processing (whole, fine ground, dry rolled, and steam-flaked) with respect to digestion with growth performance in feedlot cattle fed an otherwise conventional corn-based finishing diet.

Materials and Methods

Trial 1. One hundred twenty crossbred steers (approximately 25% Brahman, with the remainder Hereford, Angus, Shorthorn, and Charolais breeds in various proportions) with an average initial BW of 311 kg were used in a 112-d feeding trial. Steers were blocked by BW and randomly allotted to 20 pens (6 steers per pen). Pens were 43 m^sup 2^, with 22 m^sup 2^ of overhead shade, automatic waterers, and 2.4-m fence-line feedbunks. Treatments were 1) SFC (density = 0.31 kg/L), 2) DRC (density = 0.58 kg/L), 3) GC, and 4) WC. Ingredient compositions of the dietary treatments are shown in Table 1. The SFC was prepared as follows. A chest situated directly above the rollers (46 × 61 cm, corrugated) was filled with 441 kg of yellow corn and then brought to a constant temperature of 102°C at atmospheric pressure using steam. The grain was steamed for 20 min before starting the rollers. Approximately 454 kg of the initial steam-processed grain that exited the rollers during the warm-up of the rollers was set aside and not fed to the cattle in this study. The roller tension was adjusted to provide a flake density of 0.31 kg/ L (24 lb/bushel). The average retention time in the steam chamber was approximately 30 min. The SFC was allowed to air-dry before use in the diet preparation. The DRC was prepared by rolling corn in the absence of steam with the rollers tensioned to provide a density of 0.58 kg/L (45 Ib/ bushel). The GC was prepared by grinding corn in a hammer mill (Bear Cat #1A-S; Westerns Land and Roller Co., Hastings, NE). Particle size distribution of dry grain samples was determined using a USA Standard Testing Sieve (AST ME-11; Fisher Scientific, Pittsburgh, PA). Diets were prepared at weekly intervals and stored in plywood boxes located in front of each pen. The DM content of complete mixed diets was determined weekly, immediately following diet preparation. Steers were allowed free access to dietary treatments. Fresh feed was provided twice daily. Fecal grab samples were collected from each pen at weighing and analyzed for starch (Zinn, 1990). Upon initiation of the study, steers were implanted with Synovex-S® (Fort Dodge Animal Health, Overland Park, KS) and re-implanted at d 56 with Revalor-S® (Intervet, MiIlsboro, DE).

In the calculation of steer performance, BW was reduced 4% to adjust for digestive tract fill. Hot carcass weights were obtained from all steers at time of slaughter. Estimates of steer performance were based on pen means. Final BW used for calculating steer performance was determined by dividing carcass weight by the average dressing percentage for all steers. Assuming the primary determinant of energy gain is BW gain, energy gain was calculated as follows: EG = (0.0493BW^sup 0.75^) ADG^sup 1.097^ (NRC, 1984), where EG is the daily energy deposited (Mcal/d), and BW is the mean shrunk BW (full BW × 0.96). Maintenance energy expended (Mcal/d; EM) was calculated as follows: EM = 0.077W^sup 0.75^ (Lofgreen and Garret, 1968). The NE value of the diets for maintenance and BW gain were obtained using the quadratic formula: x = (-b ± the square root ofb^sup 2^ - 4ac )/2c, where a = -0.877DMI (kg/d), b = 0.877EM 0.41DMI EG, c = -0.41 EM, and dietary NE^sub g^ = 0.877NE^sub m^ - 0.41 (Zinn and Shen, 1998). The trial data were analyzed based on a randomized complete block experimental design according to the following statistical model: Y^sub ij^ = φ B^sub i^ T^sub j^ E^sub ij^, where B^sub i^ is block, T^sub j^ is treatment, and E^sub ij^ is residual error, using pen means as the experimental units. Treatment effects were tested using orthogonal contrasts (Hicks, 1973): SFC vs DRC, GC, WC; WC vs DRC, GC; and DRC vs GC.