Extruded Corn Meal as a Partial Replacement for Steam Flaked Corn in Finishing Diets for Feedlot Cattle: Growth Performance and Digestive Function of Feedlot Cattle

Sixty-four Holstein steers (247 ± 4 kg) were used in a 70-d experiment to evaluate the effects of partial replacement of steam flake corn (SFC) with extruded corn meal (EC) on growth performance and dietary net energy. Treatments consisted of a steam flaked corn-based finishing diet containing 0%, 10%, 20%, or 30% EC, where EC replaced 0%, 15%, 30%, or 45% of SFC (DM basis). Replacement of SFC with increasing levels of EC did not affect (P > 0.10) ADG, DMI, and gain efficiency. When EC replaced 15% to 30% of SFC, observed dietary NE was 99% of expected. Whereas, when EC replaced 45% of SFC, observed dietary NE was 94% of expected. Four Holstein steers (210 ± 7 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square experiment to evaluate treatment effects on characteristics of digestion. Partial replacement of SFC with EC did not affect (P > 0.10) flow of undegraded feed N and microbial N and to the small intestine, and ruminal microbial N efficiency (g microbial N/kg OM fermented). Likewise, there were no treatment effects (P > 0.10) on ruminal digestion of OM, NDF, starch and feed N. As expected, total tract digestion of starch for all treatments exceeded 99%. However, partial replacement of SFC with EC decreased total tract digestion of DM and OM (linear effect, P = 0.02), and dietary DE (linear effect, P = 0.03). These effects were more pronounced where EC replaced 45% of SFC. Partial replacement of SFC with EC did not affect (P > 0.10) ruminal pH, total VFA concentration, molar proportions of acetate, propionate, and butyrate, and estimated methane production. It is concluded that partial replacement of SFC with EC does not have a beneficial efHow to cite this paper: Buenabad, L., Jacinto, A.Y., Montano, M. and Zinn, R.A. (2019) Extruded Corn Meal as a Partial Replacement for Steam Flaked Corn in Finishing Diets for Feedlot Cattle: Growth Performance and Digestive Function of Feedlot Cattle. Open Journal of Animal Sciences, 9, 196-206. https://doi.org/10.4236/ojas.2019.92017 Received: January 23, 2019 Accepted: March 26, 2019 Published: March 29, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
The objective of grain processing is to improve feeding value and acceptability without detrimentally affecting digestive function [1]. Steam flaking corn can maximize its feeding value, largely due to enhancement of both ruminal and post-ruminal starch digestion [2] [3] [4]. Grain extrusion is a process by which ground grain is preconditioned with steam before being forced through perforated die and cut to size. Like steam flaking, extruding corn disrupts the starch matrix. Matsushima [5] proposed that extruded grains are comparable to steam-flaked grains. However, the effects of extrusion are generally more intense, resulting in a greater degree of chemical and structural transformations, including protein denaturation and starch gelatinization [6] [7], greatly enhancing starch enzymatic reactivity [8] [9]. In a direct comparison of dry rolled vs extruded corn (79% of diet DM), Gaebe et al. [10] observed that extruded corn markedly depressed DMI and ADG of feedlot steers. Depressed intake was attributed to protracted low ruminal pH of steers fed extruded corn. In a companion digestion trial, they observed that whereas extrusion markedly increased (13%) starch digestion, diet DE was not improved. This was attributed to low ruminal pH and negative associative effects on digestion of other dietary ingredients. Nevertheless, ruminal in situ comparisons demonstrated that rate of starch disappearance over time was more gradual for extruded corn vs ground corn [10]. The provision of fermentable substrate over a more prolonged period of time could have positive implications on ruminal microbial efficiency. The objective of the present study was to evaluate potential positive associative effects of extruded corn, when fed as only a partial replacement for steam flaked corn, on growth performance and characteristics of digestion in feedlot cattle.

Materials and Methods
All procedures involving animal care and management were in accordance with and approved by the University of California, Davis, Animal Use and Care Committee.

Experiment 1, Growth Performance and Dietary Energetics
Sixty-four Holstein steers with an average weight of 247 ± 4 kg were used in a 70-d experiment to evaluate the effects of partial replacement of steam flaked Open Journal of Animal Sciences corn (SFC) with extruded corn meal (EC; Matrix Nutrition, Chandler, AZ) in a finishing diet on growth performance and dietary net energy. Steers were blocked by initial weight into four weight groupings, and randomly assigned within weight groupings to 16 pens (4 steers per pen).Pens were 43 m 2 with 22 m 2 of overhead shade, automatic waters, and 2.4 m fence-line feed bunks.
Treatments consisted of a steam flaked corn-based finishing diet containing 0%, 10%, 20%, or 30% EC, where EC replaced 0%, 15%, 30%, or 45% of SFC (DM basis). The SFC was prepared as follows. A chest situated directly above the rollers (46 × 61 cm corrugated) was filled with corn and then brought to a constant temperature at atmospheric pressure of 102˚C using steam. Corn was steamed for approximately 20 min before starting the rollers. The first approximately 441 kg of steam-flaked grain was allowed to pass from the rollers before material was collected for use in the trial. This preliminary period served for warming the rolls and for adjusting the tension on the rolls to provide a flake density of 0.31 kg/L (24 lbs/bushel). The SFC was then allowed to air-dry for 3 days before feeding. Ingredient and nutrient composition of experimental diets are shown in Table 1. Diets were prepared at weekly intervals and stored in plywood boxes located in front of each pen. Steers were allowed ad libitum access to their experimental diets. Fresh feed twice daily at 06:00 and 14:00 h, allowing for approximately 5% residual. All steers were provided ad libitum access to water. Individual steers were weighed upon initiation and completion of the trial. In the calculation of steer performance live weights were reduce 4% to adjust for digestive tract fill. Estimates of steer performance were based on pen means. Pens were used as experimental units. The experimental data were analyzed as a randomized complete block design experiment according to the following statistical model: where μ is the common experimental effect, B i represents initial weight group effect (df = 3), T j represents dietary treatment effect (df = 3), and E ij represents the residual error (df = 9). Treatments effects were tested using the linear, quadratic and cubic polynomials (Statistix 10, Analytical Software, Tallahassee, FL).
Total DM flow to the duodenum and fecal excretion were estimated based on marker ratio: the relationship of Cr intake (g) vs. concentration of Cr in duodenal and fecal samples. Microbial organic matter (MOM) and N (MN) leaving the abomasum was calculated using purines as a microbial marker [21]. Organic matter fermented in the rumen was considered equal to OM intake minus the difference between the amount of total OM reaching the duodenum and MOM reaching the duodenum. Feed N escape to the small intestine was considered equal to total N entering the duodenum minus ammonia-N, MN and endogenous N (0.195 × BW 0.75 , Ørskov et al. [22]). Methane production (mol/mol glu-Open Journal of Animal Sciences cose equivalent fermented) was estimated based on the theoretical fermentation balance for observed molar distribution of VFA [23].
The effects of extruded corn meal level in diet (0, 10, 20, or 30%) on characteristics of digestion in cattle were analyzed as a balanced 4 × 4 Latin square design experiment: where: Y ijk is the response variable, µ is the common experimental effect, S i is the steer effect, P j is the period effect, T k is the treatment effect and E ijk is the residual error. Treatments effects were tested by means of linear and quadratic polynomials (Statistix 10, Analytical Software, Tallahassee, FL).

Results and Discussion
As expected, CP, NDF and starch content of EC were similar to that of SFC  [9]. With respect to steam flaking, degree of processing (flake density, steaming time, tempering) effects changes in starch enzymatic reactivity and characteristics of digestion [3] [24] [25]. However, the relationship between degree of starch gelatinization/solubility brought on by the extrusion process on characteristics of ruminal and total tract digestion has not been assessed [26].
Treatment effects on growth-performance of feedlot steers and estimated net energy values of dietary treatments are shown in Table 2. The primary goal of grain processing is to enhance feeding value and diet acceptability in a manner that will improve growth-performance with minimal detrimental effects on digestive function [1]. Partial replacement of SFC with increasing levels of EC did not affect (P > 0.10) ADG, DMI, gain efficiency, and dietary net energy. When SFC replaces dry processed corn in finishing diets, feedlot cattle ADG, gain efficiency and dietary NE are appreciably enhanced [1]. In contrast, substitution of dry rolled corn with EC (79% of diet DM) markedly depressed feedlot cattle ADG and gain efficiency [10]. Depressed intake was attributed to protracted low ruminal pH of steers fed EC. Nevertheless, when EC was fed as only a partial replacement for SFC we did not observe marked negative effects on growth-performance.
Observed dietary NE values for the basal SFC-based diet were in good (97%) agreement with expected based on tabular feed values [12].    [27]. However, microbial efficiency is affected as greater energy is expended to maintain intracellular pH [28]. Partial replacement of SFC with EC increased (linear effect, P <

Conclusion
Partial replacement of steam flaked corn with extruded corn does not have a beneficial effect on ruminal microbial efficiency and digestive function. The feeding value of extruded corn for feedlot cattle is comparable to that of steam flaked corn provided the inclusion rate does not exceed 20% of diet dry matter.