Ohio State University Extension Bulletin

Research and Reviews: Dairy

Special Circular 169-99

Site of Nutrient Digestion by Dairy Cows Fed Corn of Different Particles Size or Steam-Rolled

S. L. Callison*, J. L. Firkins1*, B. L. Hull#
*The Ohio State University Department of Animal Science
#The Ohio State University Department of Veterinary Clinical Sciences

Abstract

Five first-lactation cows were cannulated in the rumen, duodenum, and ileum and fed diets containing 50% alfalfa silage and 36.6% coarse-, medium-, or fine-ground corn (CGC, MGC, and FGC, respectively), steam-rolled corn (SRC), or a 50:50 mix of CGC and SRC (SC). The corn had a mean particle size of 4.75, 2.56, or 1.15 mm for CGC, MGC, and FGC, respectively, as evaluated by dry sieving and log-normal transformation procedures. The SC had a density of 41 lb/bu (as-is basis).

Finely grinding corn disrupted the corn kernel, considerably increasing nonstructural carbohydrate (NSC; enzymatic assay) digestibility in the rumen (about 40 percentage units, true basis, i.e., corrected for bacterial NSC flow to the duodenum); however, a relatively small increase in total tract digestibility of NSC was noted. Despite the large effect on starch digestibility, ruminal digestibility of neutral detergent fiber (NDF) was not affected as much, resulting in a small but significant shift in NDF digestion from the rumen to the large intestine. Addition of SRC to CGC linearly increased true NSC digestibility in the rumen (about 18 percentage units) but also had much smaller effects on total tract digestibility. Our results show that, although causing large changes in ruminal NSC digestibility, fine-grinding or steam-processing of corn may have only a modest impact on total tract digestibility. Based on this study and others, corn should be steam-rolled to densities less than 41 lb/bu for maximal effectiveness.

Introduction

Considerable variation in grain-processing methods occurs on farms. Sometimes, responses are seen by field nutritionists from trial-and-error adding or removing corn or from increasing or decreasing ruminal availability (e.g., high moisture vs. dry rolling) of the corn. Quantitative measurements for starch digestibilities are needed for ration-balancing software to reduce the variability of performance responses and, therefore, reduce the need for trial-and-error corrections.

Starch digestibility of the corn needs to be optimized because a 10% reduction in digestibility in the total tract may reduce availability of enough energy for three to five lbs. of milk. Conversely, if starch digestibilities in the rumen are too high, ruminal pH and NDF digestibility or dry-matter intake collectively could reduce energy availability, also decreasing milk production. Therefore, more information is needed for site of starch and fiber digestion in lactating cows fed corn processed in different ways. An additional objective was to determine if additive (associative) effects of CGC and SRC would occur when they were combined, as sometimes has been observed for feedlot beef cattle fed combinations of slower and rapidly digestible grains.

Materials and Methods

Five first-lactation Holstein cows (1,140 lb.) were surgically fitted with cannulas in the rumen and simple cannulas in the duodenum (about one foot after the beginning of the small intestine) and ileum (about one to two feet before the end of the small intestine). Cows were fed diets containing 50% alfalfa silage with no corn silage to ensure minimal quantities of starch from sources other than the corn grain (Table 1). Diets were balanced to have 42% nonfiber carbohydrates (NFC) and 32% starch (Table 2), which are near maximum levels recommended by nutritionists. Diets were mixed once daily as total mixed rations but fed twice daily. Each experimental period lasted for 14 days, with 10 days for adaptation. Chromic oxide-soyhull pellets were dosed in the ruminal cannulas at feeding for five days prior to and during the collection period. Purines were used as a bacterial marker. Corn (as fed without further processing) and alfalfa haylage (dried and ground through a 2-mm screen) were weighed into dacron bags. All samples were taken and all procedures were done as described by Younker et al. (1998) except for NSC. This analysis was modified so that, after amylase digestion of samples, sugars were quantified by gas-liquid chromatography. Ruminal measurements were statistically analyzed as repeated measures. Linear and quadratic contrasts were made for unequally spaced mean particle sizes of corn or for additivity of SRC to CGC.

Table 1. Ingredient Composition of Diets Containing Corn Processed in Different Ways.
Ingredients (% of DM)
Alfalfa silage 50.0
Corn1 36.6
Soybean hulls 6.06
Blood meal 1.78
Soybean meal, 48% CP 3.66
Soybean hull pellets2 0.90
Vitamins and minerals 1.02
1 Diets contained coarse-ground corn, medium-ground corn, fine-ground corn, steam-rolled corn, or a combination of steam-rolled and coarse-ground corn (50/50).
2 Contained 5% chromic oxide.

Table 2. Chemical Composition of Diets Containing Corn Processed in Different Ways.
  Diets1
Component CGC MGC FGC SRC SC
  -------------(% of DM)-------------
NDF 32.2 31.8 31.3 31.1 32.0
ADF 22.2 21.4 21.1 21.9 22.0
CP 17.6 17.2 16.8 17.1 17.4
NFC2 41.8 42.4 43.5 43.1 41.9
NSC3 31.3 31.9 33.4 32.3 30.4
Ca 0.78 0.75 0.77 0.78 0.80
P 0.39 0.37 0.40 0.40 0.39
Mg 0.27 0.26 0.28 0.27 0.28
K 1.47 1.49 1.49 1.45 1.53
NEL, Mcal/lb of DM4 0.74 0.76 0.79 0.77 0.73

1 CGC = coarse-ground corn; MGC = medium-ground corn; FGC = fine-ground corn; SRC = steam-rolled corn; SC = steam-rolled and coarse-ground corn (50/50).
2 NFC = non-fiber carbohydrates; calculated by difference; all NDF corrected for (NDIN x 6.25), NDIN = neutral detergent insoluble nitrogen.
3 NSC = nonstructural carbohydrates; analzyed by enzymatic determination.
4 Calculated using the equation from Weiss et al. (1993). Modified so that NEL was standardized for each period average total tract NSC digestibility of CGC, which was 91.3% (Table 3.)

Results and Discussion

Ruminal digestibility of NDF was linearly shifted from the rumen to the large intestine as particle size of corn decreased (Table 3). True ruminal digestibility of NSC increased by 40 percentage units from MGC to FGC (quadratic effect) and by about 18 percentage units (linear effect) as SRC linearly replaced CGC. Fine-grinding and steam-rolling improved total tract digestibility of NSC more moderately (seven and four percentage units, respectively).

Table 3. Least Square Means for Nutrient Digestion in Cows Fed Corn Processed in Different Ways.
  Contrast2
  Diets1   Particle Size Steam-Rolled
Item CGC MGC FGC SRC SC SE5 L Q L Q
NDF digestibility                    
 Rumen, % of total tract digestibilty 80.6 76.9 67.8 75.4 79.0 4.2 0.05 NS NS NS
 Small intestine, % of total tract digestibilty 9.7 7.7 13.2 13.5 11.5 4.8 NS NS NS NS
 Large intestine, % of total tract digestibilty 9.7 15.4 18.9 11.1 9.5 3.5 0.09 NS NS NS
 Total tract, % of intake 65.2 66.5 66.4 62.8 66.5 1.5 NS NS NS NS
NSC digestibility3                    
 True rumen, % of intake 49.8 46.5 87.0 68.0 62.1 5.0 0.01 0.02 0.02 NS
 True rumen, % of total tract digestibility 54.2 49.7 88.7 71.2 68.2 5.1 0.01 0.02 0.03 NS
 Apparent small intesting, % of total tract digestibility 47.7 60.2 19.9 36.9 46.7 7.3 0.01 0.03 NS NS
 Apparent small intesting, % of total tract digestibility 14.2 8.4 8.6 8.6 16.1 5.7 NS NS NS NS
 Apparent total tract, % of intake 91.3 92.2 98.0 95.0 89.3 1.2 0.01 0.24 0.04 0.02
Duodenal flow                    
 Nonammonia N, g/day 431 429 396 429 406 13 0.07 NS NS 0.18
 Bacterial N, g/day intake 201 205 207 217 204 92 NS NS NS NS
 NANBN4, % of N intake 44.0 42.8 37.5 41.9 40.2 202 0.06 NS NS NS
 g bacterial N/kg OM5 truly digested 22.3 24.7 19.0 23.7 21.4 1.8 0.15 0.13 NS NS
1 CGC = coarse-ground corn; MGC = medium-ground corn; FGC = fine-ground corn; SRC = steam-rolled corn; SC = steam-rolled and coarse-ground corn (50/50).
2 Linear (L) or quadratic (Q) effects of particle size or replacement of SRC for CGC. NS = P > 0.20.
3 n = 5 for all nonstructural carbohydrate (NSC) data except digestibilities in the rumenand small intestine, in which n = 4 MGC and SC.
4 NANBN = nonammonia nonbacterial N.
5 OM = organic matter and SE = standard error.

As particle size decreased, nonammonia N and nonammonia-nonbacterial N (mostly undegraded feed but some endogenous N) flows to the duodenum decreased linearly. Reducing particle size apparently disrupted the protein matrix surrounding starch, explaining the increased protein degradability in the rumen; as documented in other studies, disrupting the protein matrix helps improve starch accessibility to microbes. Higher starch degradability then probably reduced NDF digestibility in the rumen and shifted it to the large intestine, but this may have been due to a "carbohydrate effect" other than pH (Table 4) (Piwonka and Firkins, 1996). The alfalfa in the diet may have acted as a cation exchanger to reduce H+ concentration, preventing a large pH depression often noted with increased digestibility. The lack of change in VFA concentration or acetate:propionate supports the lack of pH effect seen in this trial, although VFA absorption probably increased with increased starch digestibility. There were no effects on lactation performance in this short-term study (14-day period with four days of milk measurements; see Table 5). Although corn processing had minor effects on NEL intake, an increase in NEL intake by 1.0 Mcal/day could increase milk up to 3 lb/day in a commercial setting.

Table 4. Least Square Means for Ruminal Characteristics in Cows Fed Corn Processed in Different Ways.
  Contrast2
  Diets1   Particle Size Steam-Rolled
Item CGC MGC FGC SRC SC SE3 L Q L Q
Ruminal NH3N, mg/dl 11.8 9.9 10.8 9.9 11.7 0.6 NS 0.02 0.01 0.19
Ruminal pH 5.89 6.03 5.95 5.95 5.93 0.08 NS 0.03 NS NS
Total VFA3, mM 133.8 133.5 141.1 137.9 143.8 6.3 NS NS NS NS
Acetate:propionate 2.73 2.87 2.85 2.59 2.82 0.27 NS NS NS NS
Alfalfa haylage NDF digestion in situ:                    
Potentially digestible fraction, % 50.4 53.5 52.2 54.5 53.4 1.6 NS NS 0.09 NS
Rate of digestion, /hour 0.067 0.081 0.074 0.094 0.097 0.012 NS NS 0.15 NS
Lag time, hour 1.6 1.9 1.9 3.2 2.2 0.5 NS NS 0.05 NS
Residue, % 45.9 43.5 44.0 42.7 44.0 1.3 NS NS 0.12 NS
Degestion kinetics of NSC3 from corn in situ:                    
Potentially digestible fraction, % 94.5 90.2 78.3 80.1 85.2 2.5 0.01 NS 0.01 NS
Rate of digestion, /hour 0.020 0.051 0.104 0.037 0.031 0.003 0.01 NS 0.01 NS
Lag time, hour 0.4 1.7 0.6 3.9 4.4 0.7 NS 0.20 0.01 0.03
1 CGC = coarse-ground corn; MGC = medium-ground corn; FGC = fine-ground corn; SRC = steam-rolled corn; SC = steam-rolled and coarse-ground corn (50/50).
2 Linear (L) or quadratic (Q) effects of particle size or replacement of SRC for CGC.
3 VFA = volatile fatty acids, NSC = nonstructural carbohydrates, and SE = standard error.

Table 5. Least Square Means for Lactation Performance by Cows Fed Corn Processed in Different Ways.
  Contrast2
  Diets1   Particle Size Steam-Rolled
Item CGC MGC FGC SRC SC SE3 L Q L Q
BW, lb 1159 1153 1144 1135 1109 13 NS NS NS 0.07
DMI, % of BW 3.57 3.58 3.55 3.50 3.56 0.09 NS NS NS NS
Milk, lb/day 55.0 55.9 55.0 55.4 54.1 1.3 NS NS NS NS
Milk protein, % 3.18 3.17 3.20 3.21 3.00 0.09 NS NS NS 0.09
Milk fat, % 3.50 3.58 3.57 3.39 3.24 0.11 NS NS NS 0.18
NEL Intake, Mcal/day 30.8 31.0 31.8 30.5 28.6 0.8 NS NS NS 0.07
1 CGC = coarse-ground corn; MGC = medium-ground corn; FGC = fine-ground corn; SRC = steam-rolled corn; SC = steam-rolled and coarse-ground corn (50/50).
2 Linear (L) or quadratic (Q) effects of particle size or replacement of SRC for CGC. NS = P > 0.20
3 BW = body weight, DMI = dry matter intake, and SE = standard error.

Conclusions

Our study showed that processing of corn grain greatly increased ruminal starch digestibility but only moderately increased digestibility in the total tract. Production trials are needed to verify if the changes in site of digestion of corn starch will increase milk production or if the increased ruminal starch availability would promote ruminal acidosis. However, fine grinding was a more effective processing procedure than steam rolling at 41 lb/bu.

References

Piwonka, E. J. and J. L. Firkins. 1996. Effect of glucose fermentation on fiber digestion by ruminal microorganisms in vitro. J. Dairy Sci. 79:2196-2206.

Weiss, W. P. 1993. Predicting energy value of feeds. J. Dairy Sci. 76:1802-1811.

Younker, R. S., S. D. Winland, J. L. Firkins, and B. L. Hull. 1998. Effects of replacing forage fiber or nonfiber carbohydrates with dried brewers grains. J Dairy Sci. 81:2645-2656.

1 For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210; (614) 688-3089, Fax (614) 292-1515; email:firkins.1@osu.edu

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