| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Animal Science, Michigan State University, East Lansing 48824
Corresponding author:
M. S. Allen; e-mail:
allenm{at}pilot.msu.edu.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Key Words: conservation method of corn • starch digestibility • digestion kinetics
Abbreviation key: DG = dry ground corn, EE = ether extract, HM = high moisture corn, PDNDF = potentially digestible NDF, TRDOM = true ruminally degraded OM
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Starch digestibility could also be affected by enzyme activity of ruminal fluid. The growth rate of amylolytic bacteria was affected by type of carbohydrate in vitro, and their growth rate was faster for a medium containing starch than for a medium containing glucose (Cotta, 1988). Therefore, dietary starch concentration should affect the population of amylolytic and proteolytic microbes in the rumen and enzyme activity of ruminal fluid, which could affect rate of starch digestion. Ruminal starch digestibility is also affected by rate of starch passage from the rumen, which can be affected by conservation method and dietary starch concentration. Ying and Allen (1998) reported that the passage rate of starch for dry ground corn (DG) was much greater than for ground high-moisture corn (HM) in experiments with pregnant heifers before calving and with the same animals after calving. The objective of our experiment was to evaluate effects of conservation method of corn grain on ruminal digestion kinetics for cows fed diets varying in starch concentration.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Treatments and Cows
Eight multiparous Holstein cows (55 ± 15.9 DIM; mean ± SD) from the Michigan State University Dairy Cattle Teaching and Research Center were randomly assigned to a treatment sequence within a duplicated 4 x 4 Latin square balanced for carryover effects with a 2 x 2 factorial arrangement of treatments. Factors evaluated were dietary starch concentration (21 vs. 32%) and conservation method of corn grain (HM vs. DG). Treatment periods were 21 d, with the final 10 d used to collect samples and data. Cows were cannulated ruminally and duodenally before calving. Duodenal cannulas were a soft gutter type made of Tygon and vinyl tubing (Crocker et al., 1998). The duodenum was fistulated between the pylorus and the pancreatic duct, and cannulas were placed between 10th and 11th ribs, as described by Robinson et al. (1985). Surgeries were performed at the Department of Large Animal Clinical Science, College of Veterinary Medicine, Michigan State University. At the beginning of the experiment, empty BW (ruminal digesta removed) of cows were 565.5 ± 58.5 kg (mean ± SD).
One corn hybrid (Pioneer 3730; Pioneer Hi-bred International, Inc., Johnston, IA) was grown in 1998, and half of the field was harvested as HM at a DM concentration of 63.2%. The HM was ground to mean particle size of 1863 µm and ensiled in a 2.4- x 9.0-m silage bag (Ag Bagger; Ag Bag Corp., Blair, NE). The remaining half of the field was harvested as dry corn at 89.7% DM. Dry corn was finely ground to a mean particle size of 885 µm. Nutrient composition for corn grain treatments is shown in Table 1
. Experimental diets contained either HM or DG, corn silage (50% of forage DM), alfalfa silage (50% of forage DM), a premix of protein supplements (soybean meal, distiller’s grains, and blood meal), and a premix of minerals and vitamins (Table 2). All diets were formulated for 18% dietary CP concentration and fed as a TMR.
|
|
Chromic oxide was used as a marker to estimate nutrient digestibility in the rumen and in the total tract. Gelatin capsules (1.5 oz. Tropac Inc., Airfield, NJ) containing 5 g of chromic oxide and ground spelt hulls (Wiley mill, 2 mm screen; Arthur H. Thomas, Philadelphia, PA) were dosed through the rumen cannula at 0600, 1400, and 2200 h (total of 15 g of Cr2O3 /d) from 7 to 14 d with the priming dose of 3x on d 7. Duodenal samples (1000 g) and fecal samples (500 g) were collected every 9 h from 12 to 14 d so that eight samples were taken for each cow each period, representing every 3 h of a 24-hour period to account for diurnal variation. Samples were immediately frozen at -20°C.
Sample and Statistical Analysis
All samples were composited to one sample per cow per period before drying. Duodenal samples were composited and separated into primarily solid and liquid phases using four layers of cheesecloth. Both phases were weighed, ratio of each phase was determined, and subsamples were taken from both phases according to the ratio determined for each sample to minimize sampling errors due to the segregation of samples into solid and liquid phases. Diet ingredients, orts, and feces were dried in a 55°C forced-air oven for 72 h and analyzed for DM concentration. Ruminal digesta and duodenal samples were lyophilized (Tri-Philizer MP; FTS Systems, Stone Ridge, NY). All samples were ground with a Wiley mill (1-mm screen; Arthur H. Thomas, Philadelphia, PA). Samples were analyzed for ash, NDF, ADF, lignin, indigestible NDF, CP, and starch. Ash concentration was determined after 5 h of oxidation at 500°C in a muffle furnace. Concentration of NDF and ADF were determined (method A for NDF [VanSoest et al., 1991]). Crude protein was analyzed according to Hach et al. (1987). Starch was measured by an enzymatic method (Karkalas, 1985) after samples were gelatinized with sodium hydroxide, glucose concentration was measured with glucose oxidase (Glucose kit #510; Sigma Chemical Co., St. Louis, MO), and absorbance was determined with a micro-plate reader (SpectraMax 190; Molecular Devices Corp., Sunnyvale, CA). Indigestible NDF was estimated as NDF residue after 120-h in vitro fermentation (Goering and VanSoest, 1970). Ruminal fluid for the in vitro incubations was collected from a nonpregnant dry cow fed alfalfa hay only. Concentrations of all nutrients except for DM were expressed as percentages of DM determined by drying at 105°C for more than 8 h in a forced-air oven. Corn grain was dry-sieved (Sieve apertures: 4750, 2360, 1180, 600, 300, 150, 75 µm and bottom pan) with a sieve shaker (model RX-86; W. S. Tyler Inc., Gastonia, NC) for approximately 20 min until the bottom pan weight was constant, and mean particle size of corn grain was calculated (ASAE, 1968).
Duodenal digesta and fecal samples were analyzed for concentrations of chromium. Samples were digested with phosphoric acid (Williams et al., 1962), and chromium was quantified by flame atomic absorption spectrometry (SpectraAA 220; Varian, Victoria, Australia) according to manufacturer’s recommendation. Duodenal flow of microbial OM was determined as described in a companion paper (Oba and Allen, 2003b), and true ruminally degraded OM (TRDOM) was calculated by subtracting duodenal flow of nonmicrobial OM from OM intake. Ruminal pool sizes (kg) of DM, OM, NDF, indigestible NDF, and starch were determined by multiplying the concentration of each component by the ruminal digesta DM weight (kg) except for DM. Turnover rate in the rumen, passage rate from the rumen, and ruminal digestion rate of each component (%/h) were calculated by the following equations:
 |
 |
 |
All data were analyzed using the fit model procedure of JMP (version 4, SAS Institute, Cary, NC) according to the following model:
 |
where
µ = overall mean,
Ci = random effect of cow (i = 1 to 8),
Pj = fixed effect of period (j = 1 to 4),
Tk = fixed effect of treatment (k = 1 to 4), and
eijkl = residual, assumed to be normally distributed.
Period x treatment interaction was originally evaluated, but it was removed from the statistical model because the interaction was not significant. Orthogonal contrasts were made for the effects of dietary starch concentration and conservation method of corn grain, and the interaction of dietary starch concentration and conservation method. Treatment effects and their interaction were declared significant at P < 0.05 and P < 0.10, respectively, and tendency for treatment effects and their interaction were declared at P < 0.10 and P < 0.15, respectively. When interactions of main effects were significant, treatment means were compared using Student’s t-test, and differences were declared significant at P < 0.05.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
) and for HM treatment than for DG treatment (P < 0.05). TRDOM varied from 11.3 kg/d for cows fed HM corn in high-starch diets to 7.7 kg/d for cows fed DG corn in low-starch diets. The TRDOM (% of intake) was greater for high-starch diets than for low-starch diets (P < 0.02) and for HM treatment than for DG treatment (P < 0.01), which is in agreement with previous observations (Ying et al., 1998). Although apparent digestibility of OM in the total tract was greater for HM than for DG treatment (P < 0.05), the difference in total-tract OM digestibility between HM and DG treatments was small compared with the treatment effect on true OM digestibility in the rumen. When cows were fed high-starch diets, HM treatment increased TRDOM by 20% compared with DG treatment (60.8 vs. 50.7%) but increased total-tract OM digestibility by only 6% (74.6 vs. 70.7%) because of compensatory digestion in the intestines. Previous experiments also reported that compensatory digestion in the intestines occurred when cows were fed less fermentable grains (Knowlton et al., 1998; Callison et al., 2001; Ying et al., 1998).
|
), and a tendency for interaction of main effects (P < 0.13) indicated greater difference between HM and DG treatments in high-starch diets (71.1 vs. 46.9%) than in low-starch diets (58.5 vs. 45.9%). A significant interaction of treatments was also observed for duodenal starch flow (P < 0.01), indicating greater duodenal starch flow for DG than for HM treatment when cows were fed high-starch diets (4.2 vs. 2.2 kg/d) instead of low-starch diets (2.4 vs. 1.9 kg/d). As starch passing to the duodenum increased, the amount of starch digested in the intestines increased linearly (r2 = 0.99; P < 0.0001; Figure 1). In addition, it is noteworthy that intestinal starch digestibility (% of duodenal flow) increased quadratically as duodenal starch flow increased (r2 = 0.49; P < 0.05; Figure 2). If enzyme activity limits maximum intestinal starch digestion, starch digestibility in the intestines would decrease as starch passing to the duodenum increased. However, lower intestinal starch digestibility associated with lower duodenal flow of starch in this experiment suggests that intestinal starch digestion was not limited by enzyme activity but instead by physical or chemical characteristics of dietary starch escaping digestion in the rumen.
|
|
|
Intestinal starch digestibility (% of intake) was greater for DG than for HM treatment, and total-tract starch digestibility was not affected by corn grain treatment in this experiment. The DG treatment resulted in a greater amount of starch digestion in the intestines than in the rumen, whereas the reverse was true for HM treatment. Greater DMI for cows fed DG compared with HM in high-starch diets, along with compensatory intestinal starch digestion, increased the amount of starch digested in the total tract (P < 0.01) and enhanced productivity (Oba and Allen, 2003a).
Starch Digestion Kinetics
Rate of starch passage tended to be greater for DG than for HM treatment (P = 0.07; Table 5), which is consistent with observations of Ying and Allen (1998). This may be because of greater DMI for DG than for HM treatment in high-starch diets (22.5 vs. 20.8 kg/d) or because of differences in physical characteristics between HM and DG. A significant interaction of dietary starch concentration and conservation method of corn grain was observed for rate of starch digestion (P < 0.01). Rate of starch digestion was 93% greater for HM than for DG treatment for cows fed high-starch diets (28.2 vs. 14.6%/h), but 38% greater for HM than for DG treatment for cows fed low-starch diets (16.8 vs. 12.2%/h). Corn grain treatments supplied approximately 70 and 35% of dietary starch for high- and low-starch diets, respectively. Therefore, greater effects of corn grain treatment on rate of starch digestion for high-starch diets compared with low-starch diets were at least partially because of the different proportion of dietary starch derived from corn grain for diets varying in starch concentration. However, greater dietary allocation of treatment corn grain in high-starch diets cannot totally account for the greater difference in digestion rate between HM and DG treatments for high-starch diets. Digestion rate of starch differed by 4.6 units between HM and DG treatments in low-starch diets, and high-starch diets contained approximately twice as much dietary starch from treatment corn grains compared with low-starch diets. Thus, digestion rates are expected to differ by 9.2 units between HM and DG treatments in high-starch diets, but observed digestion rate of starch differed by 13.6 units in this experiment.
|
The pool and flux method used for calculating rate of starch digestion in this experiment assumes first-order kinetics and no lag phase (Ying and Allen, 1998). However, increased rate of starch digestion for HM relative to DG treatment in high-starch diets may be because ruminal starch digestion follows second-order kinetics, and high-starch diets increased microbial amylolytic activity compared with low-starch diets. Type of carbohydrate affected growth rate of amylolytic bacteria, such as Streptococcus bovis, Ruminobacter amylophilus, Butyrivibrio fibrisolvens, and Bacteroides ruminicola (Cotta, 1988). Although substrate availability was potentially increased for HM compared with DG, regardless of dietary starch concentration, maximum rate of starch digestion might have been limited to a greater extent by enzyme activity of ruminal fluid when cows were fed low-starch diets. Simultaneous equations were developed to identify effects of dietary starch concentration on relative difference in enzyme activity for starch digestion. These equations assume that rate of starch digestion is a function of enzyme activity and potential rate of digestion is determined by substrate availability:
 |
where
a = enzyme activity for high-starch diets,
b = enzyme activity for low-starch diets,
kdHM = rate of digestion for HM corn starch,
kdDG = rate of digestion for DG corn starch,
kdX = rate of digestion for other dietary starch in high-starch diets, and
kdY = rate of digestion for other dietary starch in low starch diets.
This set of equations cannot be solved for specific values for coefficients a and b, but it can be solved for the relative relationship between coefficients a and b, which is 1.00:0.68, indicating that the enzyme activity for low-starch diets was 68% of that for high-starch diets. This calculation result should not be interpreted to mean that rate of starch digestion is maximized for the high-starch diets, but rather that enzyme activity can differ significantly for high- and low-starch diets. This finding has implications for models of rumen function. The CNCPS model (Sniffen et al., 1992) assumes first-order kinetics for digestion of nutrients and used constant digestion rate for the B1 fraction of carbohydrate (starch) to calculate ruminal starch digestibility regardless of dietary starch concentration. One interpretation of our data is that rate of starch digestion in the rumen follows second-order kinetics depending on both substrate availability and enzyme activity in the rumen.
NDF Digestion Kinetics
Digestion rate for potentially digestible NDF (PDNDF) decreased by 22% for high-starch diets compared with low-starch diets (2.58 vs. 3.30%/h; P < 0.01) and by 15% for HM compared to DG treatments (2.70 vs. 3.18%/h; P < 0.05). Despite significant treatment effects on digestion rate for PDNDF, treatment effects on ruminal NDF digestibility and total-tract NDF digestibility were not observed, possibly because of differences in passage rate for NDF. Grant and Mertens (1992) showed that rate of NDF digestion in vitro is adversely affected by low pH and presence of starch. Slower rate of PDNDF digestion for high-starch diets compared with low-starch diets in this experiment can be attributed to lower ruminal pH (Oba and Allen, 2003b). A positive relationship was observed for daily mean ruminal pH and digestion rate for PDNDF (Figure 3; P < 0.001; r2 = 0.34). However, response variables related to ruminal pH (daily mean, variance, daily minimum, time under pH 6.0, and area under pH 6.0) were not affected by corn grain treatment (Oba and Allen, 2003b). Moreover, the relationship between digestion rate for PDNDF and amount of ruminally degraded starch was not significant (P > 0.15; r2 = 0.07).
|
). Apparent NDF digestibility in the rumen was low for all treatments—averaging 18% of intake—which is less than 50% of apparent NDF digestibility in the total tract. Although low ruminal NDF digestibility can be attributed to low ruminal pH or presence of starch for high-starch diets (Grant and Mertens, 1992), reasons for similar ruminal NDF digestibility for low-starch diets are not known. Although we used higher-yielding cows, averaging more than 36 kg/d of milk yield in this experiment (Oba and Allen, 2003a), compared with some other experiments using duodenal cannulated cows reported in the literature, DMI and passage rate of NDF were not distinguishably high for this experiment. Therefore, duodenal flow of NDF might be overestimated for this experiment, resulting in relatively lower ruminal NDF digestibility as compared with other studies in the literature.
|
NRC (2001) suggested that diets with high digestibility at maintenance exhibit a greater depression in digestibility as DMI increases, compared with diets with low digestibility fed at maintenance, based on data from experiments in the literature. However, the experiments on which the regression equation is based used different cows to represent several DMI levels. Therefore, the DMI effect on nutrient digestibility is confounded by cow effect, which makes interpretation of the data more difficult. The calculation method for energy concentration of feeds in NRC (2001) uses the same discount coefficient for all nutrient components in a diet, and the discount coefficients are greater for high TDN diets regardless of nutrient components of feeds. Our data in this experiment support the idea that greater coefficients for high-TDN diets should not be used for discounting starch digestibility.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
|
ACKNOWLEDGEMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
|
FOOTNOTES |
|---|
Received for publication March 18, 2002. Accepted for publication June 11, 2002.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  M. B. Hall and G. B. Huntington Nutrient synchrony: Sound in theory, elusive in practice J Anim Sci, April 1, 2008; 86(14_suppl): E287 - E292. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. Voelker Linton and M. S. Allen Nutrient Demand Affects Ruminal Digestion Responses to a Change in Dietary Forage Concentration J Dairy Sci, October 1, 2007; 90(10): 4770 - 4779. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. J. Bradford and M. S. Allen Depression in Feed Intake by a Highly Fermentable Diet Is Related to Plasma Insulin Concentration and Insulin Response to Glucose Infusion J Dairy Sci, August 1, 2007; 90(8): 3838 - 3845. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. B. Hall and P. J. Weimer Sucrose concentration alters fermentation kinetics, products, and carbon fates during in vitro fermentation with mixed ruminal microbes J Anim Sci, June 1, 2007; 85(6): 1467 - 1478. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. L. Raeth-Knight, J. G. Linn, and H. G. Jung Effect of Direct-Fed Microbials on Performance, Diet Digestibility, and Rumen Characteristics of Holstein Dairy Cows J Dairy Sci, April 1, 2007; 90(4): 1802 - 1809. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. L. Archibeque, D. N. Miller, H. C. Freetly, and C. L. Ferrell Feeding high-moisture corn instead of dry-rolled corn reduces odorous compound production in manure of finishing beef cattle without decreasing performance J Anim Sci, July 1, 2006; 84(7): 1767 - 1777. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. L. Mentink, P. C. Hoffman, and L. M. Bauman Utility of near-infrared reflectance spectroscopy to predict nutrient composition and in vitro digestibility of total mixed rations. J Dairy Sci, June 1, 2006; 89(6): 2320 - 2326. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. B. Huntington, D. L. Harmon, and C. J. Richards Sites, rates, and limits of starch digestion and glucose metabolism in growing cattle J Anim Sci, April 1, 2006; 84(13_suppl): E14 - E. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. J. Harvatine and M. S. Allen Effects of Fatty Acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows. J Dairy Sci, March 1, 2006; 89(3): 1092 - 1103. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. Reynal and G. A. Broderick Effect of Dietary Level of Rumen-Degraded Protein on Production and Nitrogen Metabolism in Lactating Dairy Cows J Dairy Sci, November 1, 2005; 88(11): 4045 - 4064. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. R. Ipharraguerre, J. H. Clark, and D. E. Freeman Varying Protein and Starch in the Diet of Dairy Cows. I. Effects on Ruminal Fermentation and Intestinal Supply of Nutrients J Dairy Sci, July 1, 2005; 88(7): 2537 - 2555. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. C. Taylor and M. S. Allen Corn Grain Endosperm Type and Brown Midrib 3 Corn Silage: Site of Digestion and Ruminal Digestion Kinetics in Lactating Cows J Dairy Sci, April 1, 2005; 88(4): 1413 - 1424. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. C. Taylor and M. S. Allen Corn Grain Endosperm Type and Brown Midrib 3 Corn Silage: Ruminal Fermentation and N Partitioning in Lactating Cows J Dairy Sci, April 1, 2005; 88(4): 1434 - 1442. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. J. Bradford and M. S. Allen Milk Fat Responses to a Change in Diet Fermentability Vary by Production Level in Dairy Cattle J Dairy Sci, November 1, 2004; 87(11): 3800 - 3807. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Remond, J. I. Cabrera-Estrada, M. Champion, B. Chauveau, R. Coudure, and C. Poncet Effect of Corn Particle Size on Site and Extent of Starch Digestion in Lactating Dairy Cows J Dairy Sci, May 1, 2004; 87(5): 1389 - 1399. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Voelker and M. S. Allen Pelleted Beet Pulp Substituted for High-Moisture Corn: 2. Effects on Digestion and Ruminal Digestion Kinetics in Lactating Dairy Cows J Dairy Sci, November 1, 2003; 86(11): 3553 - 3561. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Oba and M. S. Allen Effects of Corn Grain Conservation Method on Feeding Behavior and Productivity of Lactating Dairy Cows at Two Dietary Starch Concentrations J Dairy Sci, January 1, 2003; 86(1): 174 - 183. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Oba and M. S. Allen Effects of Diet Fermentability on Efficiency of Microbial Nitrogen Production in Lactating Dairy Cows J Dairy Sci, January 1, 2003; 86(1): 195 - 207. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE |
