J. Anim Sci. 2008. 86:632-639. doi:10.2527/jas.2007-0057
© 2008 American Society of Animal Science
Influence of processed grains on fecal pH, starch concentration, and shedding of Escherichia coli O157 in feedlot cattle1
B. E. Depenbusch*,
T. G. Nagaraja
,
J. M. Sargeant,2,
J. S. Drouillard*,3,
E. R. Loe* and
M. E. Corrigan*
* Department of Animal Sciences and Industry, and
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan 66505
 |
Abstract
|
|---|
Manipulation of cattle diets has been proposed as a possible preharvest control measure for Escherichia coli O157. Altering hindgut fermentation through diet changes may be a means to reduce fecal shedding of E. coli O157. In Exp. 1, the objective was to determine whether fecal shedding of E. coli O157 was related to fecal starch concentration. Beginning on d 20, and every week thereafter until d 61, steers in 54 pens (6 to 7 steers per pen) were sampled (n = 122) by fecal collection and rectoanal mucosal swabs (RAMS) for E. coli O157 and fecal starch concentration determinations. Escherichia coli O157 prevalence was 3.3% in fecal samples, 4.1% as measured by RAMS, and 4.9% by fecal or RAMS samples. Steers positive for E. coli O157 contained 21% more (P < 0.05) fecal starch than steers that were negative for E. coli O157. In Exp. 2, we attempted to alter the concentration of starch escaping rumen fermentation by feeding finishing diets based on steam-flaked corn (SFC) and dry-rolled corn (DRC) to 30 heifers prescreened for being culture positive for fecal E. coli O157. Beginning on d 13, heifers were sampled (feces and RAMS) weekly to monitor fecal pH and starch concentration, and prevalence of E. coli O157. Prevalence of E. coli O157 remained above 30% for the first 13 d, but declined (P < 0.05) over the entire 7-wk period. Based on RAMS, the prevalence of E. coli O157 tended to be greater (P = 0.08) for heifers fed SFC than for those fed the DRC diet. After d 20, heifers fed DRC had greater (P < 0.05) fecal starch and lower (P < 0.05) fecal pH than heifers fed SFC. Fecal pH was negatively correlated (r = – 0.34; P < 0.05; n = 143) with fecal starch concentration. Fecal starch concentration and pH were not different (P > 0.05) for heifers that were positive or negative for E. coli O157. Our data suggest that fecal shedding of E. coli O157 was not related to fecal pH or starch concentration in cattle fed grain-based diets.
Key Words: Escherichia coli O157 • grain processing • fecal starch • feedlot cattle
|
INTRODUCTION
|
|---|
The serotype O157:H7, one of nearly 250 Shiga toxin-producing Escherichia coli implicated worldwide (Johnson et al., 2006
), is considered the most prevalent sero-type in North America, Japan, and the United Kingdom (Bielaszewska and Karch, 2000). Cattle digestive tracts, particularly the hindgut (Grauke et al., 2002; Naylor et al., 2003; Van Baale et al., 2004), are believed to be the primary reservoir for E. coli O157:H7, a human foodborne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome. Manipulation of diets fed to feedlot cattle has been proposed as a means for reducing fecal shedding of E. coli O157:H7, but results have been inconsistent (Buchko et al., 2000; Berg et al., 2004; Van Baale et al., 2004). Berg et al. (2004) showed that cattle fed corn-based diets shed more generic E. coli than do cattle fed barley-based finishing diets. Berg et al. (2004) suggested that differences in the site of digestion (rumen vs. hindgut) may have impacted fecal shedding of E. coli O157. In the rumen, the starch fraction of corn grain is not digested as extensively as starch from barley, thus resulting in greater starch concentrations entering the hindgut (Orskov, 1986; Huntington, 1997). Increasing starch concentration in the lower gastrointestinal tract will result in a secondary fermentation and increased production of VFA and, hence, reduced pH in the large intestine. The more extensively cereal grains are processed, the more starch is digested in the rumen and the less that enters the lower digestive tract (Huntington, 1997). Buchko et al. (2000) and Berg et al. (2004) suggested that low pH and the associated VFA inhibited proliferation of E. coli O157 in the large intestine. Therefore, it was of interest to determine the relationship between hindgut fermentation to fecal prevalence of E. coli O157. Our objective was to evaluate fecal starch concentration and pH in relation to shedding of E. coli O157 in feedlot cattle.
|
MATERIALS AND METHODS
|
|---|
Care and handling of the animals used in these studies were conducted under the approval of the Kansas State University Institutional Animal Care and Use Committee.
Experiment 1
Three hundred sixty-eight crossbred-yearling steers (BW = 334 ± 17 kg) were obtained from a common source and were offered ad libitum access to chopped alfalfa hay and fresh water upon arrival. Steers were allowed ad libitum access to 4 step-up diets leading to the final finishing diet that contained 78% dry-rolled corn (DRC) and 8% alfalfa hay (Table 1). Steers were housed in 54 concrete-surfaced pens (6 to 7 steers per pen), and each pen (36 m2) included overhead shade (18 m2) covering half of the pen and feed bunk. Each pen contained an automatic water fountain and 3.2 m of a fence-line feed bunk. Neither total feed samples nor individual feed ingredients were analyzed for E. coli O157.
Samples and Sampling Schedule.
Beginning on d 20, and every week thereafter until d 61 (August through September), steers from 18 of the 54 pens were individually restrained in a hydraulic working chute and sampled for E. coli O157. For our sampling scheme, we sampled the first 18 pens in the first week, second 18 pens in the second week, and third 18 pens in the third week, and back to the first 18 pens in the fourth week, and so on until the sixth week.
To determine the prevalence of E. coli O157 in steers, rectoanal mucosal swab (RAMS) samples (Rice et al., 2003; Greenquist et al., 2005) and fecal grab samples via rectal palpation were obtained. The RAMS samples were obtained according to the procedure described by Rice et al. (2003) by using a sterile foam-tipped applicator (catalog 10812-022, VWR International, Buffalo Grove, IL) inserted approximately 2 to 5 cm into the anus of each steer, and the epithelial surface was sampled using a rapid in-and-out motion. The RAMS samples were then placed into culture tubes containing 3 mL of GN-CCV broth [Gram-negative (GN) broth (Becton Dickinson, Franklin Lakes, NJ) with cefixime (0.05 mg/L; catalog 740.01, Invitrogen Corporation, Carlsbad, CA), cefsulodin (10 mg/L; catalog C8145, Sigma-Aldrich, St. Louis, MO), and vancomycin (8 mg/L; V2002, Sigma-Aldrich)] as described by Greenquist et al., 2005. Immediately after the RAMS sampling, a fecal grab sample was acquired via rectal palpation. Cattle not producing an adequate fecal sample ( > 5 g) were rerun through the restraining chute approximately 10 min after the original sampling. Fecal samples were sealed in Whirl-Pak bags (14 x 20 cm, Nasco, Ft. Atkinson, WI), and fecal samples and RAMS tubes were kept on ice and transported to the Preharvest Food Safety Laboratory in the College of Veterinary Medicine at Kansas State University for E. coli O157 isolation.
Isolation of E. coli O157.
Whirl-Pak bags containing the fecal samples were kneaded by hand for 20 to 30 s, and an approximately 1-g subsample was placed into a culture tube containing 9 mL of GN-CCV broth by using a sterile transfer stick. Culture tubes containing both RAMS and fecal samples were vortexed for 1 min, incubated at 37 ° C for 6 h, subjected to immunomagnetic separation (Dynal Inc., New Hyde Park, NY), and spread-plated onto CT-SMAC [sorbitol MacConkey agar containing cefixime (50 ng/mL) and potassium tellurite (2.5 µg/mL; Sigma-Aldrich)]. Plates were then incubated overnight (16 to 18 h), and up to 6 sorbitol-negative colonies were streaked onto blood agar plates (Remel, Lenexa, KS) and incubated for 12 to 18 h at 37 ° C. Growth on blood agar plates was tested for indole production and for O157 antigen by latex agglutination (Oxoid Limited, Basingstoke, Hampshire, UK), and the species was confirmed by API 20E identification test (Biomerieux Inc., Hazelwood, MO; Van Baale et al., 2004).
Fecal Starch Analysis.
After bacteriological sampling, the balance of the fecal material was frozen for subsequent determination of fecal starch concentration. Fecal samples from steers positive for E. coli O157 by either sampling method (fecal or RAMS; n = 41) and 239 randomly selected samples from E. coli O157-negative steers were analyzed for starch concentration. Before analysis, samples were thawed, dried in a 55 ° C forced-air convection oven, and ground through a 1-mm diam. screen by using a Thomas-Wiley laboratory mill (model 4, Thomas Scientific, Swedesboro, NJ). Dry matter of each sample was determined by drying the sample for 16 h at 105 ° C. Starch concentration in feces was determined according to the procedures described by Herrera-Saldana and Huber (1989).
Statistical Analysis
Fecal starch concentrations were analyzed using the MIXED procedure (SAS Inst. Inc., Cary, NC). The model statement included the effect of the presence or absence of E. coli O157 for each of the sampling techniques. Individual animal numbers were used as a random effect.
Experiment 2
Pretrial Phase.
Ninety-two crossbred yearling heifers (BW = 400 ± 5 kg) were begun on a common receiving diet and transitioned (step-up diets 1 to 6) to a finishing diet (step up diet 6; Table 2) containing predominantly DRC. Dry-rolled corn was processed to a mean geometric particle size of 4,072 µm (n = 23; Baker and Herrman, 2002) by using a single stack roller mill. Heifers were offered ad libitum amounts of water and feed and were fed once daily at 0800. Neither total feed samples nor individual feed ingredients were analyzed for E. coli O157. After 14 d on the DRC diet, heifers were restrained in a hydraulic working chute, and a RAMS and fecal sample were obtained from each heifer, as described in Exp. 1. On the day before sampling, heifer diets were switched from step 4 to step 5 (Table 2). Heifers that failed to yield adequate amounts of feces ( > 5 g) were separated and resampled approximately 10 min after the original sampling. Fecal samples sealed in Whirl-Pak bags, and RAMS tubes were kept cool on ice and transported to the PreHarvest Food Safety Laboratory for E. coli O157 isolation by using procedures described for Exp. 1.
View this table:
[in this window]
[in a new window]
|
Table 2. Ingredient composition and formulated nutrient values of diets fed to yearling heifers during pretrial phase of Exp. 2
|
|
Trial Phase.
Of the 92 heifers, 30 (33%) were identified as being positive for E. coli O157 based on the initial sampling of feces or RAMS. The heifers that were positive for E. coli O157 were used in an experiment with a randomized complete block design to compare the impact of grain processing methods on E. coli O157 prevalence (Fox et al., 2007). One week after sampling, heifers were stratified by BW and randomly assigned, within strata, to a finishing diet based on either steam-flaked corn (SFC; n = 15) or DRC (n = 15). Heifers assigned to the DRC diet remained on the same diet throughout the experiment. Heifers assigned to the SFC diet were transitioned over a 10-d period from the DRC diet to the SFC diet by using 3 transition diets in which SFC gradually replaced DRC as the grain source (DRC:SFC of 75:25, 50:50, and 25:75, respectively). Diets were formulated to contain 14% CP, 0.7% Ca, 0.35% P, 0.7% K, 30 mg/kg of monensin, and 9 mg/kg of tylosin (Elanco Animal Health, Greenfield, IN). The SFC was processed to a flake density of 360 g/L and had a mean geometric particle size of 5,724 µm (n = 159; Baker and Herrman, 2002).
The heifers were housed in individual pens (1.5 x 7 m) with a fence-line feed bunk (1.5 m). Half of the pen and the feed bunk were covered by an overhead roof. Dividers between pens consisted of steel pipe, and thus did not prevent contact between heifers in adjacent pens. In addition, water fountains were located such that each fountain served 2 adjacent pens. Fecal material buildup was removed from the concrete pen surfaces via scraping every 2 to 4 d. Cattle were fed once daily at 0800 and were offered ad libitum amounts of their respective diets. Total feed samples and individual feed ingredients were not analyzed for E. coli O157.
The RAMS and fecal samples were obtained from each heifer on d 20, as described in Exp. 1. A 10 x 140-mm nonsterile wooden stick (Catalog 14 410, Fisher Scientific, Pittsburgh, PA) was used to add approximately 1 g of feces to test tubes containing 15 mL of deionized water, and vortexed (Vortex-Genie 2, Vortexer Scientific Industries, Bohemia, NY). Fecal pH was then determined with a calibrated pH meter (Thermo Orion model 230Aplus, Orion Research Inc., Beverly, MA). Cattle not producing an adequate volume of fecal material after the first and second time through the restraining chute were monitored in their respective pens until a visually fresh fecal pat could be collected for pH and starch analysis. The balance of the fecal material after bacteriological sampling was frozen for starch analysis, as described in Exp. 1.
Statistical Analysis
Escherichia coli O157 prevalence (positive or negative), fecal pH, and fecal starch concentration data were analyzed using the repeated measures analysis of the MIXED procedure of SAS. The model statement included the effects of grain processing method (DRC vs. SFC) and sampling day. Body weight block served as the random variable.
|
RESULTS AND DISCUSSION
|
|---|
Experiment 1
Prevalence data for E. coli O157 are shown in Figure 1. Prevalence of E. coli O157 was 4.1% (36 of 872) as measured from RAMS samples and 3.3% (29 of 872) from fecal samples. Escherichia coli O157 was detected in 44 of 872 (4.9%) steers by either sampling technique or only 11 of 872 (1.3%) steers tested positive by both sampling techniques (Figure 1). Naylor et al. (2003) suggested that E. coli O157 specifically colonizes the lymphoid, follicle-dense mucosal epithelium at the terminal rectum. Rice et al. (2003) and Greenquist et al. (2005) concluded that sampling the terminal rectum, approximately 2 to 5 cm proximal to the rectoanal junction, was more sensitive than a fecal culture.
View larger version (12K):
[in this window]
[in a new window]
|
Figure 1. Prevalence of Escherichia coli O157 by rectoanal mucosal swab (RAMS) and fecal samples (Feces) in yearling steers (Exp. 1).
|
|
Fecal DM and starch concentrations are summarized in Table 3. Fecal starch averaged 23% among all steers ranging from a minimum of 1.2% up to a maximum of 59.6%, with a standard deviation of 11% or greater. Zinn et al. (2007) compiled fecal starch concentration data from 32 metabolism studies and showed a mean value of 5.9% with a wide range (0 to 44%) in fecal starch. Fecal DM was not correlated (P > 0.05) with E. coli O157 prevalence. Barajas and Zinn (1998) reported similar values for fecal starch concentrations in yearling heifers fed DRC-based diets (25 and 19% fecal starch when fed diets containing either 11.3 or 15.0% CP, respectively). Steers positive for E. coli O157 as determined by prevalence in fecal samples had a greater (P < 0.05) fecal starch concentration than did steers negative for E. coli O157. Likewise, fecal starch was greater (P < 0.05) for steers that tested positive by either method. But, fecal starch concentration was not different when prevalence was determined by RAMS method (P > 0.05).
View this table:
[in this window]
[in a new window]
|
Table 3. Fecal DM and starch concentration (% of DM) in yearling steers sampled for Escherichia coli O157 by rectoanal mucosal swab (RAMS) and fecal samples (Exp. 1)
|
|
Experiment 2
Pretrial Phase.
Prevalence of E. coli O157 was 16.3% (15 of 92) using RAMS samples and 23.9% (22 of 92) for fecal samples. Presence of E. coli O157 was detected by either in 30 of 92 (32.6%) heifers, whereas only 7 of 92 (7.6%) heifers tested positive by both sampling techniques. Interestingly, fecal samples were more sensitive than RAMS samples in detecting E. coli O157, which is in contrast to other published studies (Rice et al., 2003; Greenquist et al., 2005). However, Rice et al. (2003) observed that fecal samples were more sensitive than RAMS samples for the first 2 wk after experimental exposure to E. coli O157. Greenquist et al. (2005) suggested that recently exposed cattle could have less colonization of the rectoanal junction, thereby leading to reduced sensitivity of the RAMS method. Prevalence data from our study suggest that fewer animals were colonized compared with the number of animals that were shedding E. coli O157.
Trial Phase.
Prevalence data for SFC and DRC over the 50-d sampling period are summarized in Figure 2. During the 50-d sampling period, RAMS method was more sensitive than the fecal samples for 6 of the 7 sampling periods (data not shown). Prevalence of E. coli O157 in heifers as measured by fecal samples (P = 0.66, data not shown), RAMS (P = 0.08, data not shown), or either method (P = 0.10, Figure 2) remained greater than 30% for the first 14 d and then declined (P < 0.05) over time. No treatment x day interactions (P > 0.05) were observed, regardless of the sampling method.
Fox et al. (2007) showed that E. coli O157 prevalence for heifers fed finishing diets based on steam-flaked grains was greater than that observed in heifers fed dry-rolled grains, and that it remained above 30% for the first 30 d, which is in agreement with our data. In addition to dietary treatments, normal shedding patterns of E. coli O157 could have affected our prevalence data over time. Fecal shedding period can be quite variable and may range from a few days to 1 yr (Magnuson et al., 2000). Sanderson et al. (1999) and Magnuson et al. (2000) have suggested an average shedding period of 30 d. Cray and Moon (1995) indicated that fecal shedding peaked about 1 wk after inoculation of calves and decreased continually for 48 to 189 d thereafter. The use of the prescreening model to select positive animals for E. coli O157 does not take into account temporal shedding pattern of an animal. Therefore, some animals may be at the end and others at the start of their shedding patterns. However, in order to detect significant differences when analyzing binomial data such as absence or presence of E. coli O157, a high prevalence of E. coli O157 is needed. The prescreening model will likely yield prevalence levels near 50%, making this model useful in testing preharvest intervention strategies such as grain processing (Fox et al., 2007). Naylor et al. (2003) proposed that in any given population of E. coli O157-positive animals, a subset of these animals called supershedders will be shedding high numbers of E. coli O157; thereby, enhancing horizontal transmission between herd mates sharing the common water fountain was possible.
Type and level of cereal grain fed, as well as degree of grain processing, can affect the site and extent of starch digestion (Huntington, 1997). Ruminal starch fermentation is greater for finishing diets based on SFC when compared with DRC (Huntington, 1997; Barajas and Zinn, 1998). A decreased ruminal pH and ruminal acetate:propionate ratio have been reported (Zinn et al., 1995; Barajas and Zinn, 1998; Corona et al., 2006) for steers fed finishing diets based on SFC rather than DRC, which suggest a greater ruminal fermentation of starch. Fecal starch concentration was similar (P > 0.05) for SFC and DRC on d 0. After d 20, heifers fed DRC had greater (P < 0.05) fecal starch and decreased (P < 0.05) fecal pH than did heifers fed SFC (Figure 3). The correlation between fecal starch and pH was – 0.34 (P < 0.05, n = 143; Figure 4) and was lower than that previously described (Russell et al., 1980; Ledoux et al., 1985; Xiong et al., 1991; Barajas and Zinn, 1998). Possibly, an improved predictor of fecal pH may be the measurement of starch concentration exiting the small intestine rather than the large intestine. Regardless of the correlation, feeding DRC increased starch entering the lower gastrointestinal tract and increased starch in the feces, compared with feeding SFC. Figure 5 illustrates fecal starch concentration and fecal pH over time for E. coli O157-positive and -negative samples. Regardless of the sampling method used, fecal starch and pH were not different (P > 0.05) for E. coli O157-positive and -negative samples.
Theurer (1986) estimated that large amounts (up to 600 g/kg) of starch can escape ruminal fermentation and be presented for digestion in the small intestine. Increasing the amount of starch entering the small intestine above that which can be digested and absorbed will result in a secondary fermentation in the large intestine (Siciliano-Jones and Murphy, 1989; Harmon and McLeod, 2001). As hindgut fermentation increases, so will the production of VFA, hence reducing pH in the large intestine. Van Kessel et al. (2002) demonstrated a reduction in cecal and fecal pH with abomasal infusion of starch and glucose. Russell et al. (2000) speculated that a lower pH ( < 5.5) in the large intestine is a more favorable environment for survival and growth of acid-resistant E. coli. However, Buchko et al. (2000) suggested that a lower fecal pH ( < 6.3) and the associated VFA inhibited proliferation of E. coli O157:H7 in the large intestine. Other studies have demonstrated an inhibitory effect of VFA, in particular propionic acid, on E. coli O157:H7 (Rasmussen et al., 1993; Horii et al., 1998). Results from Berg et al. (2004) showed that fecal pH and prevalence of E. coli O157 were lower for cattle fed corn compared with cattle fed barley-based diets. Corn is less digestible in the rumen than barley (Huntington, 1997), thereby presenting more undigested starch to the large intestine, which would favor increased hindgut fermentation (Orskov, 1986; Duncan et al., 1991; Berg et al., 2004). Studies with cattle (Hovde et al., 1999) and sheep (Kudva et al., 1997) showed that a hay-based diet resulted in greater colonization of E. coli O157:H7 compared with a grain-based diet. Berg et al. (2004) suggested that their results agreed with those of Kudva et al. (1997) and Hovde et al. (1999) in that the forage-fed animals, which had the greatest colonization of E. coli O157:H7, would likely have a higher colonic pH. In addition, Bach et al. (2005) showed that E. coli O157:H7 persisted longer in the feces from cattle fed barley than in the feces of cattle fed corn diets. The authors speculated that this may be partly due to the lower fecal pH from cattle fed corn, compared with those fed barley. In our study (Figure 2
), we observed a decreased prevalence (P 
0.10) of E. coli O157 for cattle fed DRC compared SFC. A review by Huntington (1997) showed that starch from SFC is 11% more ruminally digested than the starch from DRC. Therefore, cattle fed DRC-based diets would have more starch presented to the large intestine for increased fermentation and VFA production. Our results seem to be in agreement with Berg et al. (2004), Buchko et al. (2000), and Horii et al. (1998).
Van Kessel et al. (2002) abomasally infused 778 g/d of starch hydrolysate or 888 g/d of glucose and found lower (P < 0.01) fecal pH compared with that of steers abomasally infused with water. Total aerobic bacterial concentrations in the feces were also greater (P < 0.01) with starch hydrolysate and glucose infusions, but total coliforms, E. coli, and acid-resistant E. coli concentrations were not different (P > 0.05) with carbohydrate infusions. They concluded that the amount of starch entering the large intestine affects cecal fermentation and microbial populations, but did not affect acid-resistant E. coli. Results from this study suggest that fecal shedding of E. coli O157 is not correlated to fecal starch concentration or fecal pH.
|
Footnotes
|
|---|
1 This is contribution No. 06-48-J from the Kansas Agricultural Experiment Station, Manhattan, Kansas. 
2 Current address: Centre for Public Health and Zoonoses, and Department of Population Medicine, University of Guelph.
3 Corresponding author: jdrouill{at}ksu.edu
Received for publication January 22, 2007.
Accepted for publication November 18, 2007.
|
LITERATURE CITED
|
|---|
Bach, S. J., K. Stanford, and T. A. McAllister. 2005. Survival of Escherichia coli O157:H7 in feces from corn- and barley-fed steers. FEMS Microbiol. Lett. 252:25–33.[CrossRef][Medline]
Baker, S., and T. Herrman. 2002. Evaluating particle size. MF-2051. Kansas State Univ., Manhattan.
Barajas, R., and R. A. Zinn. 1998. The feeding value of dry-rolled and steam-flaked corn in finishing diets for feedlot cattle: Influence of protein supplementation. J. Anim. Sci. 76:1744–1752.[Abstract/Free Full Text]
Berg, J., T. McAllister, S. Bach, R. Stilborn, D. Hancock, and J. LeJeune. 2004. Escherichia coli O157:H7 excretion by commercial feedlot cattle fed either barley- or corn-based finishing diets. J. Food Prot. 67:666–671.[Medline]
Bielaszewska, M., and H. Karch. 2000. Non-O157:H7 Shiga toxin (verocytotoxin)-producing Escherichia coli strains: Epidemiological significance and microbiological diagnosis. World J. Microbiol. Biotechnol. 16:711–718.[CrossRef]
Buchko, S. J., R. A. Holley, W. O. Olson, V. P. J. Gannon, and D. M. Veira. 2000. The effect of different grain diets on fecal shedding of Escherichia coli O157:H7 by steers. J. Food Prot. 63:1467–1474.[Medline]
Corona, L., F. N. Owens, and R. A. Zinn. 2006. Impact of corn vitreousness and processing on site and extent of digestion by feedlot cattle. J. Anim. Sci. 84:3020–3031.[Abstract/Free Full Text]
Cray, W. C., Jr., and H. W. Moon. 1995. Experimental infection of calves and adult cattle with Escherichia coli O157:H7. Appl. Environ. Microbiol. 61:1586–1590.[Abstract]
Duncan, R. W., J. R. Males, M. L. Nelson, and E. L. Martin. 1991. Corn and barley mixtures in finishing diets containing potato process residue. Prod. Agric. 4:426–432.
Fox, J. T., B. E. Depenbusch, J. S. Drouillard, and T. G. Nagaraja. 2007. Dry-rolled or steam-flaked grain-based diets and fecal shedding of Escherichia coli O157 in feedlot cattle. J. Anim. Sci. 85:1207–1212.[Abstract/Free Full Text]
Grauke, L. J., I. T. Kudva, J. Won Yoon, C. W. Hunt, C. J. Williams, and C. J. Hovde. 2002. Gastrointestinal tract location of Escherichia coli O157:H7 in ruminants. Appl. Environ. Microbiol. 68:2269–2277.[Abstract/Free Full Text]
Greenquist, M. A., J. S. Drouillard, J. M. Sargeant, B. E. Depenbusch, S. Shi, K. F. Lechtenberg, and T. G. Nagaraja. 2005. Comparison of rectoanal mucosal swab cultures and fecal cultures for determining prevalence of Escherichia coli O157:H7 in feedlot cattle. Appl. Environ. Microbiol. 71:6431–6433.[Abstract/Free Full Text]
Harmon, D. L., and K. R. McLeod. 2001. Glucose uptake and regulation by intestinal tissues: Implications and whole-body energetics. J. Anim. Sci. 79(Suppl. E):E59–E72.[Abstract/Free Full Text]
Herrera-Saldana, R., and J. T. Huber. 1989. Influence of varying protein and starch degradabilities on performance of lactating cows. J. Dairy Sci. 72:1477–1483.[Abstract/Free Full Text]
Horii, T., S. Barua, T. Kimura, S. Kasugai, K. Sato, K. Shibayama, S. Ichiyama, and M. Ohta. 1998. Heterogeneity of phenotypic and genotypic traits including organic-acid resistance in Escherichia coli O157 isolates. Microbiol. Immunol. 42:871–874.[Medline]
Hovde, C. J., P. R. Austin, K. A. Cloud, C. J. Williams, and C. W. Hunt. 1999. Effect of cattle diet on Escherichia coli O157:H7 acid resistance. Appl. Environ. Microbiol. 65:3233–3235.[Abstract/Free Full Text]
Huntington, G. B. 1997. Starch utilization by ruminants: From basics to the bunk. J. Anim. Sci. 75:852–867.[Abstract/Free Full Text]
Johnson, K. A., C. M. Thorpe, and C. L. Sears. 2006. The emerging clinical importance of non-O157 Shiga toxin producing Escherichia coli. Clin. Infect. Dis. 43:1587–1595.[CrossRef][Medline]
Kudva, I. T., C. W. Hunt, C. J. Williams, U. M. Nance, and C. J. Hovde. 1997. Evaluation of dietary influences on Escherichia coli O157:H7 shedding by sheep. Appl. Environ. Microbiol. 63:3878–3886.[Abstract]
Ledoux, D. R., J. E. Williams, T. E. Stroud, G. B. Garner, and J. A. Paterson. 1985. Influence of forage level on passage rate, digestibility and performance of cattle. J. Anim. Sci. 61:1559–1566.[Abstract/Free Full Text]
Magnuson, B. A., M. Davis, S. Hubele, P. R. Austin, I. T. Kudva, C. J. Williams, C. W. Hunt, and C. J. Hovde. 2000. Ruminant gastrointestinal cell proliferation and clearance of Escherichia coli 0157:H7. Infect. Immun. 68:3808–3814.[Abstract/Free Full Text]
Naylor, S. W., C. Low, T. E. Besser, A. Mahajan, G. J. Gunn, M. C. Pearce, I. J. McKendrick, D. G. E. Smith, and D. L. Gally. 2003. Lymphoid follicle-dense mucosa at the terminal rectum is the principal site of colonization of enterohemorrhagic Escherichia coli O157:H7 in the bovine host. Infect. Immun. 71:1505–1512.[Abstract/Free Full Text]
Orskov, E. R. 1986. Starch digestion and utilization in ruminants. J. Anim. Sci. 63:1624–1633.[Abstract/Free Full Text]
Rasmussen, M. A., W. C. Cray, Jr., T. A. Casey, and S. C. Whipp. 1993. Rumen contents as a reservoir of enterohemorrhagic Escherichia coli. FEMS Microbiol. Lett. 114:79–84.[CrossRef][Medline]
Rice, D. H., H. Q. Sheng, S. A. Wynia, and C. J. Hovde. 2003. Rectonal mucosal swab culture is more sensitive than fecal culture and distinguishes Escherichia coli O157:H7-colonized cattle and those transiently shedding the same organism. J. Clin. Microbiol. 41:4924–4929.[Abstract/Free Full Text]
Russell, J. B., F. Diez-Gonzalez, and G. N. Jarvis. 2000. Potential effect of cattle diets on the transmission of pathogenic Escherichia coli to humans. Microb. Infect. 2:45–53.[CrossRef][Medline]
Russell, J. R., A. W. Young, and N. A. Jorgensen. 1980. Effect of sodium bicarbonate and limestone additions to high grain diets on feedlot performance and ruminal and fecal parameters in finishing steers. J. Anim. Sci. 51:996–1002.[Abstract/Free Full Text]
Sanderson, M. W., T. E. Besser, J. M. Gay, C. C. Gay, and D. D. Hancock. 1999. Fecal Escherichia coli O157:H7 shedding patterns of orally inoculated calves. Vet. Microbiol. 69:199–205.[CrossRef][Medline]
Siciliano-Jones, J., and M. R. Murphy. 1989. Nutrient digestion in the large intestine as influenced by forage to concentrate ratio and forage physical form. J. Dairy Sci. 72:471–484.[Abstract/Free Full Text]
Theurer, C. B. 1986. Grain processing effects on starch utilization by ruminants. J. Anim. Sci. 63:1649–1662.[Abstract/Free Full Text]
Van Baale, M. J., J. M. Sargeant, D. P. Gnad, B. M. DeBey, K. F. Lechtenberg, and T. G. Nagaraja. 2004. Effect of forage or grain diets with or without monensin on ruminal persistence and fecal Escherichia coli O157:H7 in cattle. Appl. Environ. Microbiol. 70:5336–5342.[Abstract/Free Full Text]
Van Kessel, J. S., P. C. Nedoluha, A. Williams-Cambell, R. L. Baldwin, VI, and K. R. McLeod. 2002. Effects of ruminal and postruminal infusion of starch hydrolysate or glucose on the microbial ecology of the gastrointestinal tract in growing steers. J. Anim. Sci. 80:3027–3034.[Abstract/Free Full Text]
Xiong, Y., S. J. Bartle, and R. L. Preston. 1991. Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers. J. Anim. Sci. 69:1707–1718.[Abstract]
Zinn, R. A., C. F. Adam, and M. S. Tamayo. 1995. Interaction of feed intake level on comparative ruminal and total tract digestion of dry-rolled and steam-flaked corn. J. Anim. Sci. 73:1239.[Abstract]
Zinn, R. A., A. Barreras, L. Corona, F. N. Owens, and R. A. Ware. 2007. Starch digestion by feedlot cattle: Predictions from analysis of feed and fecal starch and nitrogen. J. Anim. Sci. 85:1727–1730.[Abstract/Free Full Text]
Top
Abstract
INTRODUCTION
) or dry-rolled corn (
) over a 7-wk period (Exp. 2).
