Metabolic response of the gastrointestinal tract of turkeys to diets with different levels of mannan-oligosaccharide

Metabolic Response of the Gastrointestinal Tract of Turkeys to Diets with Different Levels of Mannan-Oligosaccharide Z. Zdunczyk,*,1 J. Juskiewicz,* J. Jankowski,† E. Biedrzycka,* and A. Koncicki‡ *Institute of Animal Reproduction and Food Research of Polish Academy of Sciences, Tuwima 10, 10-747 Olsztyn, Poland; †Department of Poultry Science, and ‡Department of Poultry Disease, Warmia and Mazury University, Oczapowskiego 5, 10-718 Olsztyn, Poland pH of ileal and cecal contents were unaffected by dietary treatments. The highest ammonia concentration in the cecal digesta was associated with a low dose of mannan in a diet, and the concentration was reduced to the control level when both higher doses of MOS were used. Bacterial enzyme activity remained unaffected by experimental treatments. The concentration of short-chain fatty acids in the ceca decreased with increasing amounts of MOS in a diet, especially in the case of acetate. Dietary MOS did not significantly affect the cecal populations of Bifidobacterium and Lactobacillus. The population of cecal Escherichia coli was decreased, especially by the medium and high experimental treatments.

ABSTRACT Different levels of dietary mannan-oligosaccharide (MOS) administered for 16 wk to commercial male turkeys were evaluated for their efficacy on performance and on microbial activity in the digestive tract. The following levels of MOS were used in a diet: low (0.1% during the entire study), medium (0.4 and 0.2% in the first and second 8-wk periods, respectively), and high (1.0 and 0.4% in the first and second 8-wk periods, respectively). After 16 wk of experimental feeding, the diet intake was similar in all groups examined, whereas the live BW was significantly higher in groups with medium and high levels of MOS compared with the control group and birds fed a diet containing a low level of mannan. The

(Key words: mannan-oligosaccharide, gastrointestinal tract, metabolism, bacteria, turkey) 2005 Poultry Science 84:903–909

the first period of their life (4 wk), their cecal metabolism changed with some positive as well as negative effects (Jus´kiewicz et al., 2003). Gastrointestinal tracts of animals host several hundred species of bacteria. In the composition of the lower gastrointestinal tract, obligatory anaerobes predominate, including Bacteroides, Prevotella, Porphyromonas, Bifidobacterium, Peptostreptococcus, Clostridium, and Eubacterium (Macfarlane et al., 1995; Yan and Gilbert, 2004). Common intestinal commensals include aerobes or facultative anaerobes such as Enterobacteriaceae, Streptococcus, Enterococcus, Staphylococcus, and Lactobacillus; however, their counts are usually low. Bacterial composition may be affected by diet composition, especially by specific saccharides. In considering the possibility of total antibiotic restrictions in the future and potential benefits of MOS in poultry feeding, the effects of MOS on the growth as well as health status of birds need to be further explored. The objectives of this research were to evaluate the influence of dietary MOS on performance of turkeys and their intestinal health traits. Turkey growth and feed efficiency were

INTRODUCTION The use of antibiotic growth promoters in feed for poultry is banned in many countries because of the issue of antibiotic resistance in certain bacteria (Patterson and Burkholder, 2003). A fraction of the Saccharomyces yeast outer cell wall, mannan-oligosaccharide (MOS), was introduced as a feed additive for poultry over 10 yr ago (Hooge, 2003). MOS is thought to act by binding and removing pathogens from the intestinal tract as well as stimulating the immune system (Newman, 1994; Spring et al., 2000). Other oligosaccharides that are used as prebiotics, such as fructooligosaccharide, oligofructose, and inulin, are thought to selectively enrich beneficial bacterial populations. The levels of dietary MOS varied by trial and by feed phase in different studies, but in most research on poultry dietary MOS was used in small doses (0.05 to 0.20%), probably for economical reasons (Hooge, 2003). Our previous study with young turkeys fed a diet with 0.1 to 0.4% MOS indicated that although there was no significant influence on the growth of birds during

2005 Poultry Science Association, Inc. Received for publication April 22, 2004. Accepted for publication January 12, 2005. 1 To whom correspondence should be addressed: [email protected].

Abbreviation Key: MOS = mannan-oligosaccharide; SCFA = shortchain fatty acid.

903

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ZDUNCZYK ET AL. TABLE 1. Composition (%) and nutritive value of basal diet Feeding period, wk Component Basal concentrate Wheat Corn Soybean meal Fish meal Meat meal Soybean oil Vitamin and mineral mix1 NaCl Limestone Monocalcium phosphate DL-Met (99%) L-Lys HCl (99%) L-Thr Calculated chemical composition ME, kcal/kg Crude protein, % Crude fiber, % Crude fat, % Lys, % Met + Cys, % Ca, % P available, % Na, % Cl, %

1–4

5–8

9–12

24.56 20.00 42.00 3.00 5.00 1.90 1.00 0.13 0.62 2.03 0.30 0.37 0.09

28.13 20.00 41.00 3.00 — 3.50 1.00 0.25 0.80 2.60 0.27 0.40 0.05

21.00 31.78 34.00 3.00 — 5.40 1.00 0.28 0.95 2.70 0.27 0.31 0.11

2,725 28.77 3.40 4.40 1.80 1.16 1.30 0.72 0.15 0.21

2,797 25.93 3.67 5.51 1.65 1.06 1.14 0.69 0.15 0.27

2,981 22.92 3.08 7.64 1.40 0.978 1.19 0.67 0.16 0.28

13–16 40.54 25.00 26.00 — — 4.50 1.00 0.25 1.10 1.90 0.12 0.39 0.02 3,004 18.78 3.00 6.56 1.20 0.73 1.01 0.50 0.14 0.23

1 For 1 to 4, 5 to 8, and 9 to 16 wk of feeding the vitamin and mineral premix supplied per kilogram of diet: vitamin A, 15,000, 13,000, and 12,000 IU; vitamin E, 40, 35, and 30 mg, respectively. For 1 to 16 wk of feeding the vitamin and mineral premix supplied per kilogram of diet: Se, 0.3 mg; Mn, 150 mg; Zn, 90 mg; Fe, 60 mg; Cu, 15 mg; I, 1 mg; Diclazuril, 1 mg; vitamin D3, 4,500 IU; vitamin K3, 2.5 mg; vitamin B1, 3.5 mg; vitamin B2, 10 mg; vitamin B6, 6 mg; vitamin B12, 0.03 mg; folic acid, 2 mg; biotin, 0.36 mg; niacin, 75 mg; panthotenic acid, 21 mg; choline, 600 mg.

examined after 16-wk administration of diets with different levels (0.1 to 1.0%) of MOS preparations. Cecal metabolism (activity of microbial enzymes, ammonia and shortchain fatty acid (SCFA) concentration, pH of digesta), and bacterial status in the ceca were analysed. To evaluate cecal microflora changes in our study, Bifidobacterium and Lactobacillus were chosen as markers of beneficial microflora and Escherichia coli as a marker of opportunistic bacteria.

MATERIALS AND METHODS Birds and Diets The experiment was conducted on 156 BUT-92 male poults that were 3 d old and were randomly assigned to 1 of 4 dietary treatments. Dietary treatments were made in triplicate, each with 13 birds. The birds were given free access to mash diets consisting of the basal diet and up to 1% of MOS given instead of corn (Table 1). An experimental diet contained a low (0.1% during the entire experiment), medium (0.4 and 0.2% in the first and the second 8-wk period, respectively), or high (1.0 and 0.4% in the first and the second 8-wk period, respectively) level of MOS preparation.3

Procedures The entire experiment lasted 16 wk; after that period the birds were weighed and killed according to the recommendations for euthanasia of experimental animals (Close et al., 1997). The selected parts of the digestive tract (gizzard, small intestine, ceca, colon, and liver) were removed and weighed.

Bacterial Analysis Three groups of microflora (Bifidobacterium, Lactobacillus, and Escherichia coli) were determined in the cecal contents. All bacterial determinations were conducted immediately after sampling. Samples were collected, and Bifidobacterium and Lactobacillus were counted according to the procedure described by Biedrzycka et al. (2003), and E. coli were counted on McConkey Purple agar medium after 24 h of incubation at 37°C. The 1 L of medium (pH 7.4 ± 0.1) contained 20 g of peptone-tryptone, 10 g of lactose, 5 g of bacteriological bile, 5 g of sodium chloride, 0.07 g of bromocresol purple, and distilled water. The microbiological results were expressed as log colonyforming units per gram of cecal contents.

Measurement of Cecal Properties 2

Hatchery Grelavi Co., Ketrzyn, Poland. Biomos, Alltech, Inc., Nicholasville, Ky. Model 301, Hanna Instruments (www.hannainst.com/index.cfm).

3 4

Ileal and cecal pH were measured with a microelectrode and a pH/ION meter.4 Samples of ileal (from the

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METABOLIC RESPONSE OF THE GASTROINTESTINAL TRACT TABLE 2. Effect of dietary mannan-oligosaccharide (MOS) on diet intake and BW of turkeys Dietary intake, kg 1–4 wk 5–8 wk 9–16 wk BW, kg At 4 wk At 8 wk At 16 wk FCR,1 kg/kg 1–4 wk 5–8 wk 9–16 wk Weight of gastrointestinal tract, g/kg of BW Gizzard Liver Small intestine Ceca Colon

0%

0.1%

0.4/0.2%

1.0/0.4%

SEM

1.48 5.83 25.83

1.46 5.95 25.44

1.50 5.96 26.31

1.52 5.77 26.39

0.07 0.17 0.72

0.96 3.96 13.74b

0.95 4.09 13.80b

0.97 4.04 14.44a

0.96 3.90 14.21a

0.08 0.03 0.08

1.65 1.91 2.64

1.63 1.89 2.62

1.64 1.91 2.53

1.71 1.92 2.56

0.07 0.06 0.11

9.35 11.66 12.92 3.21 1.22a

9.88 12.36 12.89 2.88 0.97b

8.94 11.90 12.02 2.82 0.86b

9.11 12.66 13.36 2.99 1.02b

0.23 0.20 0.24 0.08 0.04

Values within each row with different superscripts are different at P ≤ 0.05. Feed conversion ratio.

a,b 1

middle part of ileum) and cecal contents were transferred to microfuge tubes, which were immediately stored at −70°C. The cecum wall was flushed clean with ice-cold saline, blotted on filter paper, and weighed (cecal wall weight). The same procedure was repeated for the small intestine and colonic tissue. Dry matter of cecal and ileal digesta was determined at 105°C. The ammonia extracted and trapped in a solution of boric acid was determined by direct titration with sulfuric acid (according to the standard Conway’s method).

SCFA and Activity of Microbial Enzymes Analysis Cecal (or ileal) digesta were also measured for SCFA concentration by gas chromatography.5 The samples of digesta (of about 0.2 g) were weighed, mixed with 0.2 mL of formic acid, diluted with deionised water, and centrifuged at 10,000 × g for 5 min. Supernatant was loaded onto the chromatography glass column 2.5 m × 2.6 mm, containing commercial packing: 10% SP-1200/ 1% H3PO4 on 80/100 Chromosorb W AW.6 The chromatograph was coupled to a flame ionization detector, and we used a column temperature of 110°C, detector temperature of 180°C, and injector temperature of 195°C. Cecal SCFA pool size was calculated as the sum of SCFA concentration in digesta and cecal digesta mass. The microbial enzyme activity in the cecal (ileal) digesta was measured by the rate of p- or o-nitrophenol release from their nitrophenylglucosides according to the modified method of Djouzi and Andrieux described by Jus´kiewicz et al. (2002). The following substrates7 were used: for β-glucuronidase, p-nitrophenyl-β-D-glucuronide; for α-galactosidase, p-nitrophenyl-α-D-galactopyranoside;

5

Shimadzu GC 14A, Shimadzu Co., Kyoto, Japan. Supelco Co., Bellefonte, PA. Sigma Chemical Co., St. Louis, MO.

6 7

for β-galactosidase, o-nitrophenyl-β--galactopyranoside; for α-glucosidase, p-nitrophenyl-α-D-glucopyranoside; and for β-glucosidase, p-nitrophenyl-β-D-glucopyranoside. The reaction mixture contained 0.3 mL of substrate solution (5 mM) and 0.2 mL of a 1:10 (vol/vol) dilution of the cecal sample in 100 mM phosphate buffer (pH 7.0) after centrifugation at 10,000 × g for 15 min. Incubation was carried out at 37°C, and p-nitrophenol was quantified at 400 nm and o-nitrophenol at 420 nm after addition of 2.5 mL of 0.25 M cold sodium carbonate. The enzymatic activity was expressed as micromoles of product formed per min (IU) per gram of digesta in the cecal (ileal) sample. The protein content in the supernatant was determined by the Lowry’s method (1951) using BSA as the standard.

Data Analysis The results of the experiment were analyzed using the one-way ANOVA test, and significant differences between groups were determined by the Duncan’s multiple range test. Differences were considered significant at P ≤ 0.05. Coefficients of linear correlation and regression were calculated for the cecal parameters of cecal content and dry matter percentage, SCFA concentration, and microflora.

RESULTS During 16 wk of feeding, dietary intake was similar for all groups (Table 2). There were no differences in the live BW of experimental birds at the age of 4 and 8 wk; however, addition of MOS preparation to a diet had a significant influence on the final BW (16 wk). The turkeys fed a diet containing the medium (MOS-0.4/0.2% group) or high level of MOS (MOS-1.0/0.4% group) gained significantly more weight than the birds in the control and MOS-0.1% groups. Feed conversion ratio index was unaffected by mannan addition to a diet. Diversified supplementation of a diet with MOS had no influence on the

906

ZDUNCZYK ET AL. TABLE 3. Effect of dietary mannan-oligosaccharide (MOS) on ileal and cecal digesta parameters Item Ileal digesta pH Dry matter, % Cecal digesta Content, g/kg of BW pH Dry matter, % Dry matter, g/kg of BW Ammonia, mg/g Ammonia, mg/kg of BW Protein,1 mg/g Protein,1 mg/kg of BW Enzyme activity, U/g of fresh cecal digesta α-Glucosidase β-Glucosidase α-Galactosidase β-Galactosidase β-Glucuronidase

0%

0.1%

0.4/0.2%

1.0/0.4%

SEM

6.30 17.6

6.29 17.9

6.51 18.0

6.53 17.3

0.05 0.43

1.70 6.88 19.1a 0.321 0.91b 1.48b 0.560 0.916

2.11 6.87 16.5b 0.348 1.18a 2.42a 0.560 1.166

2.23 6.80 18.1ab 0.399 1.09ab 2.42a 0.593 1.335

2.22 6.92 18.4a 0.407 0.98ab 2.21a 0.578 1.276

0.15 0.05 0.32 0.03 0.04 0.17 0.01 0.07

8.87 2.32 30.3 50.9 26.1

7.35 2.42 32.7 44.8 26.1

9.17 2.68 36.7 48.0 30.3

8.79 2.67 35.7 52.5 31.6

0.55 0.18 2.34 3.87 2.08

Values within each row with different superscripts are different at P ≤ 0.05. According to the method of Lowry et al. (1951).

a,b 1

relative weight of the gizzard, small intestine, ceca, or liver tissue, whereas the relative colonic tissue weight of turkeys fed a diet without MOS was significantly higher than that in the groups fed with MOS. The pH value and dry matter concentration of ileal digesta were unaffected by the experimental treatments. The SCFA were not identified in the ileal digesta, and the microbial enzyme activity was found low. The pH of cecal digesta was not influenced by supplementation with MOS (Table 3). The cecal dry matter concentration was the lowest in the MOS-0.1% group and enhanced in the turkeys consuming medium and high doses of MOS. The lowest hydration of cecal digesta occurred in the control group. A positive correlation was observed between MOS content in the diet and cecal content as well as dry matter content in the cecal digesta. Relatively low correlation coefficients (0.22 to 0.24) were not insignificant. A decreasing tendency was observed in the cecal ammonia concentration along with an increasing level of MOS supplementation. The lowest ammonia concentration (mg/g of digesta) and content (mg/kg of BW) were observed in birds fed the control diet (without MOS). The protein concentration and activity of particular bacterial enzymes (α-, β-glucosidase; α-, β-galactosidase; and β-glucuronidase) in the cecal digesta were not influenced by dietary treatments. A negative correlation was observed (r = −0.381, P ≤ 0.05) between the concentration of SCFA in the cecal digesta (y) and MOS content in the diet (x) (Table 4). The SCFA concentration in the cecal digesta could be described by the formula y = 37.32 − 17.61x. The greatest concentration of total SCFA was in the control group, whereas lower concentrations were mannan. That reduction effect was observed especially in the case of acetate. The concentrations of propionate and butyrate were similar in all groups. The production of SCFA in the ceca (expressed as µmol/kg of BW) did not differ among groups, but a lower total content of SCFA was observed

with a higher dose of MOS. If the C2:C3:C4 profile is considered, the MOS supplementation (all levels) decreased acetate and increased propionate as well as butyrate proportions in the profile compared with the control treatment. In the cecal digesta, the Bifidobacterium and Lactobacillus counts were determined as genera entirely positive for host’s health, and E. coli was a typical representative of opportunistic bacteria (Table 5). In the control group of turkeys, the populations of Bifidobacterium and Lactobacillus had the highest counts. The E. coli count was lower by 2 log units than those of Bifidobacterium and Lactobacillus. In the groups of turkeys fed diets containing the increasing doses of MOS, Bifidobacterium and Lactobacillus counts were not different from the controls. The E. coli counts were significantly lower in the MOS-0.4/0.2% and MOS-1.0/0.4% groups than in the control. A negative correlation was observed (r = −0.551, P ≤ 0.01) between E. coli count in the cecal digesta and MOS content in the diet. The E. coli count in the cecal digesta was described by the formula: y = 6.60 − 1.31x, where y = log colonyforming units per gram, and x = percentage of MOS in the diet.

DISCUSSION The BW of turkeys at the age of 16 wk were significantly influenced by MOS addition to the diets. The heaviest turkeys were those fed a medium level of dietary MOS (0.4 and 0.2% in the first and second 8-wk periods, respectively). The highest level of dietary MOS (1.0 and 0.4% in the first and second 8-wk periods, respectively) also significantly improved the BW gain of turkeys compared with the groups without or with a low dose of MOS. The BW of turkeys from the control group and those from the low MOS group (0.1% during the entire experiment) were similar. The same tendency for growth was noted in our previous study (Jus´kiewicz et al., 2003), in which

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METABOLIC RESPONSE OF THE GASTROINTESTINAL TRACT TABLE 4. Effect of dietary mannan-oligosaccharide on short-chain fatty acid (SCFA) concentration and content in cecal digesta

Concentration, µmol/g Total SCFA Acetate Propionate Isobutyrate Butyrate Isovalerate Valerate Content, µmol/kg of BW Total SCFA pool Acetate pool Propionate pool Isobutyrate pool Butyrate pool Isovalerate pool Valerate pool

0%

0.1%

0.4/0.2%

1.0/0.4%

SEM

41.1a 29.2a 3.47 0.71 5.00 0.99 1.68a

34.0ab 22.2ab 3.11 0.62 5.60 1.05 1.45ab

27.7b 16.2b 3.37 0.53 5.36 0.96 1.35ab

27.0b 15.9b 3.72 0.57 4.85 0.93 1.09b

2.23 2.00 0.16 0.03 0.23 0.04 0.09

70.4 50.9 5.95 1.22 8.78 1.74 2.67

72.9 45.6 6.92 1.44 12.8 2.44 3.28

63.2 37.4 7.99 1.24 12.9 2.28 3.07

59.6 35.3 8.27 1.29 10.9 2.02 2.38

6.64 5.18 0.68 0.13 1.26 0.20 0.38

Values within each row with different superscripts are different at P ≤ 0.05.

a,b

turkey poults were fed for 4 wk with starter diets containing 0.1, 0.2, and 0.4% MOS. Although there was no significant influence of MOS on BW gains, the turkeys fed 0.2%-MOS and 0.4%-MOS gained 4.93 and 3.20% more, respectively, and the turkeys fed a diet containing 0.1%MOS gained 1.07% less than the control birds. This nonsignificant trend was consistent with the reports that a low MOS in a diet (0.1%) can improve the performance of turkeys (Savage and Zakrzewska, 1997; Fairchild et al., 2001). Although MOS is not used as a substrate in microbial fermentation, it can modify microflora fermentation to favor nutrient availability to the host (Ferket et al., 2002). In a study with turkeys, Ferket (2002) observed that dietary supplementation of MOS preparation reduces total SCFA content of the jejunum digesta by about 40%. Most of that effect is attributed to a reduction in propionic acid. Another benefit from dietary inclusion of MOS is a decrease in jejunum digesta pH and ammonia concentration (Ferket, 2002). In the present study, SCFA were not detected in the ileal digesta, bacterial enzyme activity was low, and pH was not affected by an inclusion of MOS. The site of bacterial fermentation in birds is mainly the ceca (Annison et al., 1968). In our experiments, after 16 wk of feeding none of the dietary treatments had any significant effect on pH status or bacterial enzyme activity in the ceca. The concentration of ammonia in the cecal digesta increased after low-level MOS supplementation (0.1%), but in the MOS-1.0/0.4% group (high-dose) ammonia was reduced to the level observed in control turkeys fed a diet without mannan. In our previous study on

young turkeys (Jus´kiewicz et al., 2003), the cecal ammonia concentration was significantly reduced, but the pH of cecal digesta was higher in turkeys consuming 0.1, 0.2, or 0.4% of MOS in a diet for 4 wk compared with the controls. The production of ammonia is closely related to bacterial activity and is associated with certain toxic events in the gastrointestinal tract, hence ammonia is considered to be a potential tumor promoter in the hindgut (Salminen et al., 1998). The SCFA, mainly acetate, propionate, and butyrate, are the major end products of bacterial fermentative reactions in the hindgut. Some researches have suggested that different amounts or different fermentability of oligosaccharides added to a diet correlate better with the cecal pool (expressed as µmol/kg of BW) than with the cecal concentration of SCFA (Remesy et al., 1992; Campbell et al., 1997). In a study (Jus´kiewicz et al., 2003) on young turkeys, the higher the amounts of MOS added to a diet the smaller the cecal SCFA pool is; however, the cecal SCFA concentrations are not changed by mannan treatments. In the present study, after 16 wk of feeding, the total SCFA pool was not affected by the experimental treatments, but SCFA concentration was lower after MOS addition, especially with medium and high levels. Mannan-oligosaccharides are primarily added to poultry diets to prevent colonization by Salmonella (Oyofo et al., 1989; Spring et al., 2000). In different studies with poultry, the levels of dietary MOS supplementation varied by trial and feed phase, ranging from 0.05 to 0.40%. In the present study, the supplementation of a diet with low (0.1%), medium (0.4 and 0.2% in the first and second

TABLE 5. Cecal microflora of turkeys (log cfu/g of cecal content)

Bifidobacterium Lactobacillus Escherichia coli

0%

0.1%

0.4/0.2%

1.0/0.4%

SEM

8.80 8.85 6.86a

8.53 8.54 6.33ab

8.90 8.49 5.95b

8.56 8.56 5.81b

0.09 0.08 0.11

Values within each row with different superscripts are different at P ≤ 0.05.

a,b

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ZDUNCZYK ET AL.

8-wk periods, respectively), and high (1.0 and 0.4% in the first and second 8-wk periods, respectively) dietary MOS did not affect the numbers of Bifidobacterium and Lactobacillus cecal populations, whereas the 2 higher doses of MOS significantly reduced E. coli counts by 1 log unit. The trend for MOS to decrease beneficial bacteria is not a desirable response, because healthy populations of these bacteria play important roles in maturation and development of a strong immune system and as a barrier against intestinal pathogens. MOS is hydrolyzed by different lactobacilli and some bifidobacteria; however, they seem to be less fermentable by intestinal microflora than fructooligosaccharides (Zentek et al., 2002). Perhaps, dietary supplementation with MOS requires the addition of another bifidogenic factor. The species and strains of Bifidobacterium and Lactobacillus characteristic for poultry ceca (Mead, 1997) should be taken into consideration in preliminary studies. MOS rarely influence the intestinal microflora, except for pathogens. MOS, given to 3-d-old chicks in the amount of 0.4% had no effect on cecal concentrations of lactobacilli, enterococci, or anaerobic bacteria and did not significantly reduce the concentrations of cecal coliforms although they were numerically lower (Spring et al., 2000). When brewers dried yeast, providing 0.16% dietary MOS, was fed to pigs, the total coliforms, E. coli, and Clostridium perfringens in feces were not affected by the diet, but Bifidobacterium counts were lower and Lactobacillus counts were higher (White et al., 2002). In studies on dogs, MOS were able to decrease the count of total aerobes and tended to increase Lactobacillus populations (Swanson et al., 2002), or they did not affect ileal microflora, including C. perfringens, Bifidobacterium, Lactobacillus, aerotolerant anaerobes, E. coli, and coliforms, and tended to lower fecal populations of C. perfringens only (Strickling et al., 2000). Hooge (2003) explained the mode of MOS action by which broiler or turkey performance could be improved. The adsorption of pathogenic bacteria containing type 1 fimbrae via a receptor analog mechanism (strongly binding to, and decoying pathogens away from, the sugarcoated intestinal lining) or via agglutination of MOS by different bacterial strains (Oyofo et al., 1989; Spring et al., 2000) could improve intestinal function or gut health (e.g., increased villi height, uniformity, and integrity; Loddi et al., 2002). Immune modulation could also be improved by stimulating gut-associated and systemic immunity as a nonpathogenic microbial antigen, providing an adjuvantlike effect (Ferket et al., 2002). We found that although a limited amount of MOS (0.1%) had no impact, elevated (medium and high) levels of dietary MOS significantly increased live BW after feeding for 16 wk. The cecal metabolism was affected by dietary MOS to some extent. Although MOS did not change the cecal pH or the bacterial enzyme activity, when applied at medium and higher doses it decreased ammonia as well as SCFA concentration (mainly acetate) in the cecal digesta. Dietary MOS had no significant effect on the cecal populations of Bifidobacterium and Lactobacillus, whereas the populations of cecal E. coli were de-

creased, especially by the medium and high experimental concentrations. A decreasing tendency observed in the populations of Bifidobacterium and Lactobacillus at all experimental doses might indicate that MOS are not easily used by bacteria in the digestive tract of poultry and that the diet requires cosupplementation.

ACKNOWLEDGMENTS This study was supported by the State Committee for Scientific Research, Grant 3P06Z02124.

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