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Research Center, Agriculture and Agri-Food Canada; Lethbridge, AB, T1J 4B1, Canada,
and
* Isfahan University of Technology, Isfahan, Iran; and
and
Chr. Hansen BioSystems, Milwaukee, WI 53214
3 Correspondence:
Box 3000 (phone: 403-317-2235; fax: 403-382-3156; E-mail:
beauchemin{at}em.agr.ca).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Acidosis • Beef Cattle • Enterococcus • Microbial Flora • Probiotics • Propionibacterium
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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There has been some indication that certain bacterial DFM may also have beneficial effects in the rumen. In particular, bacterial DFM may help prevent ruminal acidosis, characterized by low ruminal pH and high ruminal concentrations of lactic acid, conditions that can lead to acute metabolic acidosis (Owens et al., 1998). Nocek et al. (2000) reported a reduced risk of acidosis in dairy cows fed a combination of lactate-producing bacteria, Lactobacillus and Enterococcus, presumably because the presence of these bacteria caused the rumen microflora to adapt to the presence of lactate within the rumen. Inoculation of an in vitro fermentation with the lactate-utilizing ruminal bacterium Megasphaera elsdenii prevented lactate accumulation when a highly fermentable substrate was used (Kung and Hession, 1995). Propionibacterium may have a similar effect because these bacteria convert lactate and glucose to acetate and propionate.
Supplementing cattle diets on a daily basis with lactate-utilizing bacteria and(or) lactate-producing bacteria has been shown to improve the feed efficiency and ADG of feedlot cattle (Swinney-Floyd et al., 1999; Galyean et al., 2000; Rust et al., 2000). However, mechanisms that explain the beneficial effects of bacterial DFM supplements are not clearly understood.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Six ruminally cannulated steers (mean BW 670 kg) were used in a replicated 3 x 3 Latin square design, balanced for residual effects, to investigate the effects of supplementing feedlot cattle diets with bacterial DFM. The ruminal cannulas measured 10 cm in diameter and were constructed of soft plastic (Bar Diamond, Parma, ID). Surgical preparation of steers was done several months before the start of the study, and during that time the steers received a diet containing 80% hay. Twenty-eight days before the experiment, the steers were adapted to the high-grain experimental diet.
In each period, steers received one of the following treatments: 1) control, 2) Propionibacterium P15 (P15), and 3) Propionibacterium P15 plus Enterococcus faecium EF212 (PE). Chr. Hansen BioSystems (Milwaukee, WI) prepared the bacteria specifically for this study. The viability of the preparation was checked prior to starting the experiment, and results were in agreement with the stated quantity of colony-forming units. The bacteria were blended with whey powder to supply 1 x 109 cfu/g of carrier. The blend, or whey powder alone for control, was top-dressed onto the diet of each steer once daily at the time of feeding (10 g/[steer/d]).
The experimental diet contained 87% steam-rolled barley, 9% whole crop barley silage, and 4% supplement (DM basis), as shown in Table 1
. The diet was prepared daily using a feed mixer. Feed was offered once daily at 0900 for ad libitum intake (at least 10% orts). Feed offered and refused was recorded daily.
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In order to minimize carry-over effects from period to period, on the last day of Periods 1 and 2, the rumen of each steer was emptied manually and the contents were placed into the rumen of the next steer within the square that was to receive that treatment. Thus, each steer started the period with rumen contents corresponding to the same treatment it was fed.
Samples of barley silage, concentrate, and diet were collected weekly. Dry matter was determined on a portion of each weekly sample, and the DM contents were used to adjust the silage-to-concentrate ratio of the diet when necessary. Weekly fresh samples of barley silage, concentrate, and diet were composited by period and retained for chemical analysis. Samples of orts were collected the last 7 d of the period and composited by animal. Samples were dried and DMI for each steer was calculated based on the feed DM offered and orts DM refused.
Ruminal pH was measured continuously for 6 d of each period (d 15 to 20) using indwelling electrodes. An electrode (model PHCN-37; Omega Engineering, Stamford, CT) was inserted into the rumen of each steer through the cannula. A weight was attached to the electrode to ensure that it remained in the ventral sac. In addition, a protective shield with large openings that allowed ruminal fluid to percolate freely was placed around the electrode to prevent it from coming in contact with the ruminal epithelium. The electrodes were removed from the rumen 1 h before feeding each day and calibrated with pH 4.0 and pH 7.0 standards. The pH was measured every 5 s, and an average of these readings was recorded every 15 min using a data logger. Ruminal pH data were summarized daily for each steer in each period as daily mean pH, maximum and minimum pH, amount of time in which pH was below 5.8 or below 5.5, and area between the curve and pH 5.8 or pH 5.5. The area was calculated by adding the absolute value of negative deviations in pH from pH 5.8 for each 15-min interval. The number was then expressed as pH units x hours. The duration that pH remained below the threshold indicates the duration of subclinical acidosis, whereas the area between the curve and the pH threshold indicates the severity of subclinical acidosis.
To evaluate the potential effects of DFM on ruminal digestion, samples of concentrate, barley silage, alfalfa hay, and wheat straw were incubated in sacco for 24 h from 0900 on d 14 to 0900 on d 15. The silage, hay, and straw were dried at 55°C for 48 h and ground through a 4.5-mm screen. Following grinding, these feeds were sieved to remove particles > 1 cm in length. The concentrate, which consisted of steam-rolled barley and supplement, was not ground. Five grams of DM was then weighed into small bags (10 x 20 cm) made of monofilament Pecap polyester (pore size, 51 ± 2 µm; B. & S. H. Thompson, Ville Mont-Royal, QC, Canada) and heat-sealed. Four replications of each sample were incubated in each animal for each period. Individual bags were soaked in warm water for 10 min, and quadruplicate bags were added to mesh retaining sacks that allowed ruminal fluid to percolate among the bags. All bags were removed at the end of the incubation period and machine washed in cold water until the effluent was clear. Bags were dried at 60°C for 48 h and weighed to determine DM disappearance.
At 0, 6, and 12 h after feeding on d 14 and d 20, rumen contents were obtained from four sites within the rumen (reticulum, dorsal and ventral sacs, and the mat), composited, and strained through a polyester monofilament fabric (Pecap 7-1180/59, mesh opening 1,180 µm, Tetko Inc., Scarborough, ON, Canada). Five milliliters of filtrate was preserved by adding 1 mL of 25% (wt/vol) HPO3 to determine VFA and lactate, and 5 mL of filtrate was preserved by adding 1 mL of 1% (wt/vol) H2SO4 to determine NH3. The samples were subsequently stored frozen at -20°C until analyses. An additional 5 mL of filtrate was preserved using 5 mL of methyl green formalin-saline solution for protozoa enumeration (Ogimoto and Imai, 1981). These protozoal samples were stored at room temperature and protected from light until counting. Protozoa were counted with the aid of a hemocytometer chamber. Duplicate preparations of each sample were counted, and if either value differed from the average by more than 10%, the counts were repeated.
Samples for ruminal bacterial enumeration were taken at 6 h after feeding on d 14. Rumen contents were sampled from four sites in the rumen, composited, blended anaerobically under oxygen-free CO2, strained through a polyester monofilament fabric (Pecap 7-1180/59, mesh opening 1,180 µm, Tetko Inc, Scarborough, ON, Canada), and serially diluted in 0.1% (wt/vol) buffered peptone. Diluted samples were inoculated (0.2 mL/tube) into selective carbohydrate agar by the roll tube technique for enumeration of amylolytic and lactate-utilizing bacteria. The selective carbohydrate agar was based on Medium 10 of Caldwell and Bryant (1966) containing 0.1% (wt/vol) soluble starch or 50 mM lactic acid as the main energy source for amylolytic and lactate-utilizing bacteria, respectively. Streptococcus bovis-like bacteria were counted using membrane-Bovis media described by Oragui and Mara (1984). Lactobacillus sp. bacteria were enumerated using DeMan Rogosa Sharpe agar (DeMan et al., 1960). The plates were incubated in an anaerobic cabinet under an O2-free atmosphere of CO2:H2 (90%:10%) following a 1-h aerobic preincubation at room temperature. This aerobic preincubation eliminates O2-sensitive ruminal bacteria that don’t produce lactic acid (Yanke and Cheng, 1998). Reinforced clostridial medium (Becton Dickinson Microbiology Systems, Sparks, MD) was used to detect P15, although this medium is not specific. Bacterial colonies were detected at the 10-5 level in ruminal and fecal samples after 5 d of incubation; however, none of these were distinct colonies produced from P15, and therefore the results were not reported. All other cultures were incubated at 39°C for 48 h prior to enumeration, and numbers were reported as colony-forming units.
Fecal samples were obtained on d 15 for enumeration of bacteria associated with the DFM treatments. Samples were taken just before feeding directly from the rectum of each steer using a plastic bag. Fecal samples were serially diluted in 0.1% buffered peptone, and diluted samples were inoculated (0.1 mL/plate) into DeMan Rogosa Sharpe agar and reinforced clostridial medium agar.
On the last day of each period, blood samples were taken at 0, 6, and 12 h after feeding from the jugular vein of each steer, alternating sides at each collection. The blood was collected in a 10-mL Vacutainer tube (Na heparin), and blood pH and CO2 were analyzed within 1 to 2 h. Packed cell volume was determined by collecting a sample in a microhematocrit capillary tube, sealing the end, centrifuging for 6 min with a hematocrit centrifuge, and reading with a microcapillary reader (model MH, International Equipment Company, Boston, MA). A subsample (1mL) of the plasma was centrifuged at 16,000 x g for 2 min (Eppendorf 5415, Hamburg, Germany) to remove fibrinogen, and the supernate was used to analyze glucose and lactate dehydrogenase (LDH) using a VetTest analyzer (model 8008, IDEXX Lab, Westbrook, ME).
Feed DM was determined by oven drying at 55°C for 48 h. Analytical DM content of the samples was determined by drying at 135°C for 3 h (AOAC, 1990). The OM content was calculated as the difference between DM and ash contents (AOAC, 1990). The concentration of CP was determined by flash combustion (Carlo Erba Instruments, Milan, Italy). The NDF and ADF contents were determined by the methods described by Van Soest et al. (1991) with amylase and sodium sulfite used in the NDF procedure. The processing index of the barley grain was calculated by measuring the volume weight of the barley after processing, expressed as a percentage of its volume weight before processing on a DM basis, to quantify the degree of processing of the barley grain (Yang et al., 2000). The effective fiber content of barley silage was measured as the sum of the proportion of the sample retained on the top and bottom sieves of the Penn State Particle Separator.
Ruminal VFA were separated and quantified by gas chromatography (Hewlett-Packard 5890; Agilent Technologies, Mississauga, ON) with a 30-m (0.32 mm i.d. x 1.0 µm film thickness) fused-silica capillary column (Nukol, Supelco/Sigma-Aldrich Canada Ltd., Oakville, ON) and a flame ionization detector. Ammonia content of ruminal samples was determined by the method described by Weatherburn (1967) modified to use a plate reader. Lactic acid was determined by gas chromatography after derivatization with boron trifluoride-methanol (Supelco/Sigma-Aldrich).
For each period, means for individual steers were calculated for all variables. Data for bacterial counts were converted prior to analysis using a log transformation. Data were analyzed with the mixed model procedure of SAS (SAS Inst. Inc., Cary, NC) to account for effects of square, steer within square, period within square, and treatment. Square, steer, and period were considered as random effects, and the restricted maximum likelihood method was used to estimate the variance components. Differences among means were tested using single degree-of-freedom contrasts. A split plot in time model was used for variables measured over time, including DMI, ruminal pH measurements, blood measurements, VFA, lactate, NH3, and protozoa. In that case, the model accounted for effects of square, steer within square, period within square, treatment, square x steer x period x treatment, time, and time x treatment. Effects of square, steer within square, period within square, and treatment were tested using square x steer x period x treatment as the error term, whereas, time and time x treatment were tested against the residual error. Treatment effects were declared significant at P < 0.05 and trends were discussed at P < 0.10, unless otherwise noted.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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The chemical composition of the diet is presented in Table 1
. The diet composition was typical of diets fed commercially to feedlot cattle in southern Alberta, Canada. Daily DMI measured during the last 7 d of the period averaged 9.29 kg/d and was not affected by treatment (Table 2). Others have also reported no effect on DMI of growing cattle fed bacterial DFM (Lactobacillus and Propionibacterium) (Galyean et al., 2000; Rust et al., 2000). Evaluation of daily DMI over the period did not reveal a treatment x day interaction, indicating that the intake of cattle fed the different treatments responded in the same manner throughout the period. Occasionally, steers reduced their intake presumably due to ruminal acidosis. However, the drop in intake, in most cases, lasted only a single day, recovering thereafter.
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). Furthermore, no differences among the treatments were observed for the other ruminal pH variables measured, including minimum and maximum pH, time pH < 5.8, area under pH 5.8, time pH < 5.5, and area under pH 5.5, which averaged 5.17, 6.43, 12.44 h/d, 6.63 units • h, 9.07 h/d, and 3.4 units • h, respectively. The pH values reported in this study are lower than previously reported for feedlot cattle fed high-grain diets based on barley grain. Krause et al. (1998) reported a mean ruminal pH of 6.16 for cattle with ad libitum access to diets containing 95% concentrate containing mainly barley (DM basis). Beauchemin et al. (2001) reported for feedlot cattle fed high-grain diets containing barley that mean pH values ranged between pH 5.79 and 6.06 and that minimum pH values ranged from 5.21 to 5.56, depending on the extent to which the grain was processed.
The pattern of diurnal fluctuation of ruminal pH was similar among treatments; there was no interaction between treatment and time (Figure 1). The highest pH values were observed just before the morning feeding, and the lowest pH values occurred 11 to 13 h after feeding. Ruminal pH was high before the morning feeding because the cattle tended to ruminate at night and eat during the daytime. After feeding, the pH dropped as expected, due to the highly fermentable carbohydrate content of this diet. There was also a significant effect of day for all pH variables, which indicates the importance of measuring pH for several days. These day-to-day variations in ruminal pH did not correspond directly to changes in DMI from day to day.
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Low ruminal pH in steers was due primarily to an accumulation of VFA rather than lactate. In the present study, ruminal concentrations of lactate were extremely low and below the level of detection (< 1 mM). Harmon et al. (1985) found L-lactate in the rumen to average 2.07 mM in cattle fed a diet containing 70% concentrate (DM basis). Similarly, Hristov et al. (2001) reported that L-lactate concentrations in ruminal fluid from cattle fed diets containing 62 or 95% (DM basis) barley remained below 1.4 mM throughout the study. During acute acidosis in cattle characterized by ruminal pH between 3.9 and 4.5 (Dunlop, 1972), ruminal lactate concentration exceeds 50 mM (Dunlop, 1972; Nagaraja et al., 1985). However, only a slight increase in lactate concentration has been noted during subclinical acidosis, with concentrations less than 10 mM (Harmon et al., 1985; Burrin and Britton, 1986). Brown et al. (2000) reported a ruminal lactate concentration of 48 mM on d 0 of feeding, but lactate remained below 1 mM afterward for steers fed to induce acute acidosis.
Neither DFM influenced the total VFA, concentrations of propionate, isobutyrate, and isovalerate, or the acetate-to-propionate ratio (Table 2). However, the concentration of acetate in ruminal fluid was greater (P < 0.05), and the concentration of valerate tended to be lower (P < 0.1), for steers receiving PE compared to steers receiving P15 or the control diet. These results are in contrast with a study by Kim et al. (2000), in which concentrations of propionate increased at the expense of acetate with supplementation of lactate-producing and -utilizing bacteria (L. plantarum and P. acidipropionici). Steers fed P15 had higher concentrations of butyrate (P < 0.05) compared to control steers. Others reported accumulations of butyrate when M. elsdenii, an active lactate utilizer, was grown in pure culture (Marounek et al., 1989; Slyter et al., 1992; Kung and Hession, 1995). Satter and Esdale (1968) proposed that, although acetate and propionate are important precursors of lactate in the rumen, acetate is usually only an intermediate and is used in the synthesis of butyrate, which may account for the higher butyrate concentrations, in steers fed P15. The consequence of higher levels of butyrate in the rumen of feedlot cattle is not clear. Aeillo and Armentano (1987) reported that high levels of butyrate reduced the in vitro gluconeogenic capacity of caprine liver. However, in an in vivo study conducted by Reynolds et al. (1992), infusion of butyrate had no effect on the gluconeogenic capacity of the liver in steers.
Ruminal NH3 concentration tended to be higher for steers fed P15 than for steers fed PE or control (P < 0.10); Table 2). The concentration of NH3 was affected by sampling time (P < 0.1); concentrations of NH3 at 0 h were higher than concentrations at 6 h, and concentrations at 6 h were higher than those at 12 h.
Microorganisms
A significant finding from this experiment is the effects of DFM, particularly P15, on the protozoa population (Table 3). The total protozoa count for steers fed P15 was significantly higher than those fed PE (P < 0.05) or control (P < 0.003). Most of the protozoal populations were identified as Entodinium. Higher protozoal numbers for steers fed P15 likely increased ruminal recycling of bacterial N accounting for the higher ruminal NH3 concentration observed for these steers (Veira et al., 1983; Williams and Withers, 1993; Jouany, 1996). Higher protozoal numbers may also have contributed to the higher butyrate levels observed for steers fed P15, as Entodinium tend to increase molar proportions of butyrate (Howard 1963). Protozoal number was also affected by sampling time (P < 0.10), and at 6 h, protozoa numbers were higher compared to numbers at 0 or 12 h.
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Over the course of the experiment, none of the steers were free of protozoa. The steer that experienced bloat had the lowest protozoa population (1.50 x 106/mL). Earlier reports indicated that grain-fed feedlot cattle are virtually free (Eadie et al., 1970; Lyle et al., 1981), or have dramatically reduced protozoal populations (Slyter et al., 1970; Vancer et al., 1972). Few studies have investigated the effects on ruminal protozoa of high-grain diets based on barley grain. Eadie et al. (1970) reported complete defaunation of the rumen of cattle offered barley grain for ad libitum intake. Slyter et al. (1970) observed low protozoal numbers in an experiment with four steers fed barley diets with intake restricted to 1.5% BW. However, Hristov et al. (2001) demonstrated that a large population of Entodinium persists in the rumen of cattle fed high-grain diets based on barley.
The effect of treatments on viable anaerobic bacterial counts both in the rumen and feces is shown in Table 3. The number of amylolytic bacteria in steers receiving P15 was lower (P < 0.05) than for the other steers. This decrease in the population of starch-utilizing bacteria is consistent with the increase in the protozoal population. Protozoa demonstrate predatory activity against rumen bacteria. Also, protozoa engulf starch particles along with their associated bacterial population, which would limit the substrate for the starch-utilizing bacteria and the numbers of amylolytic bacteria in the ruminal contents.
The number of Streptococcus bovis in ruminal fluid of steers fed PE was considerably lower than for steers receiving either the control or P15 treatments (Table 3). However, differences among treatments were not statistically significant. Although no attempt was made to isolate bacteriocins from the preparations used in this study, they have previously been isolated from species of the Propionibacterium (Barefoot et al., 1993) and Enterococcus (Arihara et al., 1993) genera, although the spectrum of activity and degree of growth inhibition can be variable. Bacteriocins might have played a role in the inhibition of Streptococcus bovis by the treatment containing Enterococcus.
Mean counts of Lactobacillus bacteria in rumen contents and feces were not affected by DFM treatments (Table 3). However, it should be noted that numbers of lactate-utilizing bacteria in the feces were numerically higher in steers fed DFM compared to control.
Blood Variables
Blood pH was not affected by DFM supplementation (Table 4), which is consistent with the lack of effect of DFM supplements on ruminal pH (Table 2). However, blood pH is very resistant to fluctuations because the acid-base balance is highly regulated and blood is saturated with bicarbonate (Owens et al., 1998).
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Bacterial DFM treatments had no effect on blood packed cell volume compared with control. However, blood LDH concentrations of steers fed P15 were higher (P < 0.05), and concentrations of steers fed PE were lower, compared with cattle fed the control diet. Changes in blood LDH concentration reflect the need to metabolize lactate, and LDH concentrations tend to increase during acidosis (Owens et al., 1998). It appears that providing lactate-producing bacteria together with lactate-utilizing bacteria decreased the need to metabolize blood lactate. Lower LDH concentration of steers fed PE is also consistent with lower blood CO2. Bacterial DFM treatments had no effect on blood glucose.
DM Disappearance
Supplementation with DFM had no direct effect on digestibility measured as in situ disappearance of DM at 24 h (Table 5).
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Both species of bacteria used in this study are ubiquitous in the rumen environment. Although they may not be able to compete with the rumen microflora or maintain a stable population in the rumen, it is clear that they are metabolically active and can exert effects on rumen fermentation.
There is recent evidence that supplementing cattle diets on a daily basis with some lactate-utilizing bacteria and(or) lactate-producing bacteria can improve the feed efficiency and ADG of cattle fed high-concentrate diets (Swinney-Floyd et al., 1999; Galyean et al., 2000; Rust et al., 2000). However, there is very limited published information on the mechanisms by which bacterial DFM improve animal performance, particularly for cattle adapted to high-grain diets. Although this study does not present a clear mechanism of action for bacterial DFM based on Propionibacterium or a combination of Propionibacterium and Enterococcus, the evidence suggests that bacterial DFM modify ruminal fermentation and blood variables in feedlot cattle fed highly fermentable diets. Further research is needed to clearly define the mode of action.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 The authors thank Bev Farr, Alastair Furtado, Tom Thiessen, Rena Wuerfel, and Marina Maekawa for their assistance in conducting the experiment and performing laboratory analyses and the staff of the Lethbridge Research Centre metabolism unit for care of the cattle.
Received for publication September 12, 2001. Accepted for publication January 8, 2002.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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