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Xylanase and ß-glucanase supplementation improve conjugated bile acid fraction in intestinal contents and increase villus size of small intestine wall in broiler chickens fed a rye-based diet¹

N. Mathlouthi^*,2, J. P. Lallès, P. Lepercq, C. Juste and M. Larbier^*

^* INRA, Station de Recherches Avicoles, 37380 Nouzilly, France; and INRA, Unité Mixte de Recherche sur le Veau et le Porc, 35042 Rennes, France; and INRA, Unité d’Ecologie et Physiologie du Système Digestif,78352 Jouy-en-Josas Cedex, France

² Correspondence:
phone: 0033.2.47.42.78.51; fax: 0033.2.47.42.77.78; E-mail:
nmathlouthi{at}hotmail.com.

	Abstract

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This study was performed with growing chickens (4 to 22 d of age) to evaluate the effects of feeding a rye-based diet supplemented with commercial enzyme preparation containing xylanase and ß-glucanase (Quatrazyme HP, Nutri-Tomen, France) on small intestine wall morphology, bile acid composition, nutrient digestibility, and bird performance compared with unsupplemented rye- or corn-based diets. The rye-based diet decreased (P 0.05) weight gain, feed intake, and feed efficiency and increased water intake compared with the corn-based diet. Moreover, rye consumption reduced crude fat and protein digestibility as well as apparent metabolizable energy (P 0.05). The small intestine wall showed that villus length, width, and surface were decreased in broiler chickens fed the rye-based diet compared with those fed the corn-based diet. However, crypt morphometry parameters were not affected by diet type. The concentration of conjugated bile acids in the small intestine contents of broiler chickens fed the rye-based diet was decreased (P 0.05) compared with those fed the corn-based diet. These findings suggest that feeding a rye-based diet reduces villus capacity for nutrient absorption and bile acid capacity for fat solubilization and emulsification, resulting in decreased bird performance. The addition of xylanase and ß-glucanase to the rye-based diet improved (P 0.05) weight gain, feed intake, and feed efficiency, and decreased water intake. The digestibility of nutrients and apparent metabolizable energy were also increased (P 0.05). Addition of xylanase and ß-glucanase increased (P 0.05) villus size and the villus height-to-crypt depth ratio, as well as the concentration of conjugated bile acids (P 0.05) in the small intestine contents. Exogenous enzymes improved nutrient digestibility and broiler chicken performance, probably by improving the absorption capacity of the small intestine through increased villus surface and intestinal concentration of conjugated bile acids.

Key Words: Bile Acids • Broilers • ß-glucanase • Rye • Villi • Xylan 1,4-ß-xylosidase

	Introduction

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The arabinoxylans and ß-glucans present in the endosperm cell walls of rye have been identified as a major cause of poor growth rate and low nutrient digestibility (Ward and Marquardt, 1987) in broiler chicken. These antinutritive effects of nonstarch polysaccharides are attributed to an increase in intestinal digesta viscosity (Choct and Annison, 1992b). Indigestible polysaccharides, which are known to be viscous, can act directly by increasing bile acid excretion (Garcia-Diez et al., 1996), or indirectly through the intestinal microflora, which affect the morphology of the small intestine wall (Southon et al., 1987). Therefore, the addition of exogenous enzymes is necessary to reduce the antinutritive effects of viscous nonstarch polysaccharides (Choct and Annison, 1992a). The nonstarch polysaccharide-degrading enzymes markedly increase the nutritive value of wheat (Choct et al., 1995) and rye (Bedford and Classen, 1993) in broiler chicken. This improved performance of birds fed nonstarch polysaccharide-rich cereal diets by xylanase and ß-glucanase supplementation is not due to release of simple sugars, but rather to the ability of the enzymes to prevent the formation of viscous digesta (Choct and Annison, 1992a). As reported by Yasar and Forbes (2000), the decrease in digesta viscosity after exogenous enzyme addition is most likely associated with an improvement in small intestine wall morphology.

The present study was undertaken to elucidate whether the addition of xylanase and ß-glucanase was associated with an effect on the unconjugated and conjugated bile acid concentrations and/or with a change in the gut morphology of broiler chickens fed a rye-based diet supplemented with animal fat. We used this experimental model to ensure the greatest beneficial effects of exogenous enzymes. As reported by Dänicke et al. (1999), the enzyme effect was more pronounced in nonstarch polysaccharide diets supplemented with tallow than soybean oil.

	Materials and Methods

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Animals and Diets.
Sixty 1-d-old male broiler chickens (Ross, SICAMEN, France) were housed in suspended wire cages (size: 29 x 28.5 x 36.5 cm) and received a corn-based diet. At 3 d of age, all the chickens were fasted and weighed the following day. A total of 30 chickens were distributed into three homogenous experimental groups and housed in individual cages. A plastic tray was slipped under each cage in order to collect excreta during digestive balance experiments. The room temperature was gradually decreased from 32°C at d 1 to 24°C at d 22. The light was continuous during the first 3 d, and then the lighting regimen was 23 h/d. Two diets based on either corn (610 g/kg) or rye (581 g/kg) were formulated according to the nutritional requirements for chickens (Larbier and Leclercq, 1992), and calculated using PORFAL software version 2.0 (ITP-INRA, France). Both basal diets (Table 1) were isocaloric (11.82 MJ of apparent ME/kg) and isonitrogenous (200 g of CP/kg). All diets were fed in mash form and contained no growth factors, coccidiostats, or antibiotics. The exogenous enzyme used in this trial was the commercial powdered preparation Quatrazyme HP (Nutri-Tomen, France) with xylanase and ß-glucanase activities of 28,000 and 140,000 IU per gram of product, respectively. The enzyme preparation was added to the rye-based diet at the level of 20 mg/kg of diet (560 and 2,800 IU of xylanase and ß-glucanase, respectively). Feed and water were supplied ad libitum throughout the entire experiment. Thus, the three dietary treatments were corn, rye, and rye plus enzyme preparation. The diets were given to broiler chickens from 4 to 22 d of age. Body weights were determined at 4, 18, 21, and 22 d of age. Feed and water intake was recorded individually during the entire experiment.

At the end of the experiment (22 d of age), all birds were killed by intracardiac injection with 1.5 mL of 6% sodium pentobarbital solution (Sanofi Santé, Nutrition Animale, La Ballastière, France) per kilogram of chicken live weight. The digestive tract between the gizzard and Meckel’s diverticulum was removed to obtain the duodenum plus jejunum. Intestinal contents of the duodenum plus jejunum were collected by gently finger-stripping the intestinal segments. After collection, the fresh samples of duodenal plus jejunal contents were stored at -20°C for analysis of bile acids. The ileum was isolated as the intestine between Meckel’s diverticulum and the ileocecal junction. The ileum was cut open longitudinally at the mesenteric attachment and 0.5-cm-long samples were taken from the intestinal wall, 1 cm distal to Meckel’s diverticulum for morphology measurements.

Analyses and Measurements.
For viscosity measurements, the corn- and rye-based diets and the three feedstuffs (corn, soybean meal, and rye) were milled through a 0.5-mm sieve, then an aliquot (3.5 g) was homogenized with 30 mL of acetate buffer solution (0.2 mol/L sodium acetate, pH = 4.5) and incubated for 1 h at room temperature (20°C). The diet and feedstuff suspensions were centrifuged at 1,000 x g for 15 min and the supernatant was isolated. The viscosity of the supernates was then measured as previously described (Carré et al., 1994). Viscosity was expressed as real applied viscosity (real applied viscosity = ln(_r)/g^-1•mL, where _r represents the relative viscosity calculated as the ratio of the viscosity of the sample to the viscosity of buffer).

Water, ash, crude fat, and protein for the three feedstuffs were determined according to Official European Methods (AFNOR, 1985), and starch was determined according to Carré et al. (1991). Water-insoluble cell wall content (cellulose, water-insoluble hemicellulose, water-insoluble pectic matter, lignin, and proteins) was determined according to AFNOR (1989). Soluble sugars (arabinose and xylose) were measured as previously described (Harris et al., 1988). Arabinoxylans were calculated as arabinose plus xylose. Soluble ß-glucan contents in rye, corn, and soybean meal were analyzed according to the methods of McCleary and Codd (1991).

Total fat contents of food and excreta were determined by extraction of samples with petroleum ether after boiling samples in 3 mol/L HCl for 20 min. The determination of nitrogen in food and excreta was performed with the Kjeldahl method. Fecal nitrogen in the excreta was calculated as total nitrogen minus nitrogen in the uric acid. Uric acid was analyzed by the method of Terpstra and De Hart (1974). The apparent metabolizable energy of each diet was calculated from the gross energy values of the diet and freeze-dried excreta. Gross energy values were measured using an isoperibol oxygen bomb calorimeter (Kalorimeter C7000 prozesso, IKA Laboratechnik Janke & Kunkel-STR 79219, Staufen, Germany). Apparent metabolizable energy values were corrected to zero nitrogen balance as described by Hill and Anderson (1958).

Intestine morphology measurements were determined according to the method of Goodlad et al. (1991). Villus and crypt length, width, and surface were measured using image analysis software (Optimas version 6.5, Media Cybernetics, L.P., Silver Spring, MD).

For bile acid measurements, lyophilized intestine contents (750 mg) were rehydrated in a minimal volume of distilled water. After the addition of 1 mg of HCl under sonication as internal recovery marker, fats were extracted with 100 mL of ethanol for 48 h in a Soxhlet apparatus. Free and total bile acid fractions were then each prepared from 4 mL of this ethanol extract previously adjusted to 100 mL. For free bile acids, ethanol was evaporated, the dried extract was resuspended in 20 mL of distilled water by sonication, and the pH was adjusted to 3 to 4 with HCl. The suspension was then passed through a small Lipidex 1000 column (Packard Instruments, Pharmacia, Peapack, NJ), the effluent discarded, and the bile acids eluted with 20 mL of 68% methanol (Setchell et al., 1983). For total bile acids, the Soxhlet ethanol extract (4 mL) was added with 1 mL of 10 N NaOH, and saponification and hydrolysis were carried out at 120°C for 3 h. The reaction mixture was then cooled on ice, the pH was adjusted to neutral with concentrated HCl, and the ethanol was evaporated. The extract was resuspended in 20 mL of distilled water, the pH was adjusted to 3 to 4 with HCl, and total bile acids in their free form were extracted on Lipidex 1000 as described above. Finally, free and total bile acid extracts were evaporated to dryness, redissolved in a small volume of methanol, and transferred to a small vial to be derivatized and analyzed in gas chromatography.

Statistical Analyses.
Data were statistically analyzed for treatment effect by the GLM procedures of StatView software for Windows (SAS Inst. Inc., Cary, NC). Values are given as means ± SEM, and the homogeneity of variance was checked. Mean differences were determined using Fisher’s test of least significance. The level of statistical significance was preset at P 0.05.

	Results

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Nutritional Characteristics of Feedstuffs.
Table 2 indicates that corn contained the least number of water-insoluble cell walls. In contrast, soybean meal showed the lowest content of starch and the highest content of water-insoluble cell walls. Rye contained more arabinose, xylose, and ß-glucans compared with corn or soybean meal (Table 2). Rye, characterized by the highest total of soluble arabinoxylans and ß-glucans (22 g/kg of dry matter (DM)), had the highest viscosity level. By contrast, corn had the lowest viscosity and contained the lowest total arabinoxylans and ß-glucans (0.8 g/kg of DM).

	Discussion

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The results of the present study show that the inclusion of rye instead of corn in the diet markedly depressed (P < 0.05) growth performance. Fengler and Marquardt (1988) obtained similar results when broiler chickens were fed rye water-soluble pentosans. Animal fat was added to the rye-based diet to amplify the antinutritional effects of nonstarch polysaccharides. Nevertheless, rye is the most viscous cereal, and fat digestibility depression by nonstarch polysaccharides is more pronounced in the presence of animal fat than vegetable oil (Dänicke et al., 1999). The reduced performance in the rye-fed birds was at least due to the reduction in nutrient digestibility (Sharma et al., 1997). Moreover, the rye-based diet raised water intake and the water-to-feed intake ratio. The latter finding could be partly explained by the capacity of nonstarch polysaccharides to bind water (Langhout and Schutte, 1996). The increase in digesta viscosity is thus the primary mechanism by which water-soluble nonstarch polysaccharides exert antinutritive properties (Bedford and Classen, 1993). However, this mechanism has not been fully established. One possible hypothesis is increased microbial activity in the broiler chicken small intestine. This interaction between diet and microflora in the intestinal lumen (Sharma et al., 1997) probably interferes with digestive and absorptive processes.

As reported by others (Wang et al., 1992), the results of the present study show that the digestibility of added fat is highly affected. This is partly due to the low bile acid concentration in the digesta of young birds (Polin et al., 1980; Iñarrea et al., 1989). In fact, according to the present study, it appears that the primary bile acid, chenodeoxycholic acid, was specifically decreased by rye feeding, leading to a dramatic fall in the concentration of total bile acids in the intestinal contents. This strongly suggests partial interference with the enterohepatic circulation of bile acids by rye, which might act as a bile acid sequestering agent in the intestinal lumen. As inferred from the intestinal concentration of total bile acids, which remained low in the group receiving rye plus xylanase and ß-glucanase, this physicochemical effect of rye could not be prevented by enzyme supplementation. A second effect of rye feeding was strong stimulation of the early deconjugation of taurochenodeoxycholic and taurocholic acids, which are the predominant bile acids in chicken bile (Elkin et al., 1990), but this was counteracted by enzyme supplementation. This strongly suggests the presence of some species of bacteria in the small intestine of rye-fed chickens that can deconjugate bile acids (Hylemond, 1985) and make them more readily adsorbed by dietary fiber (Kay et al., 1979), but not in those supplemented with exogenous enzymes. This coincides with our morphological results, demonstrating that intestinal mucosa was modified in chickens receiving rye alone, but not in those receiving rye plus enzymes. This damage to the small intestinal mucosa may be caused indirectly by the viscous characteristics of nonstarch polysaccharides (Stanogias and Pearce, 1985). Sakata (1987) demonstrated that an increase in bacterial activity in the gastrointestinal tract was associated with a change in the morphology of the gut wall. This reinforces the idea that exogenous enzymes might exert their beneficial action by influencing the intestinal microflora (Bedford, 2000). As a result, a decrease in total bile acid concentration—aggravated by early bacterial deconjugation, which made fat emulsification less effective (Coates et al., 1981)—and the decrease in the absorptive capacity of the intestinal mucosa might together contribute to lower fat digestibility in rye-fed broiler chickens. Furthermore, the present study indicates that feeding a rye-based diet not only reduces fat digestibility, but also reduces protein digestibility. This could be explained by bacteria overgrowth in the small intestine, which increases the loss of endogenous nitrogen (Smits et al., 1997) by incorporating amino acids into microbial proteins (Salter and Coates, 1974) and thus reduces apparent protein digestibility (Angkanaporn et al., 1994). Second, the increase in digesta viscosity might reduce the diffusion rate of digestive enzymes such as proteases (Larsen et al., 1993). Third, gut morphology is affected in a viscous environment and thus impairs the absorption process of nutrients such as amino acids (Sakata, 1987). The addition of xylanase and ß-glucanase to the rye-based diet improved nutrient digestibility and broiler chicken performance. This beneficial effect of exogenous enzymes has previously been reported in numerous studies (Choct et al., 1995; Scott et al., 1998). Moreover, water intake was reduced when broiler chickens were fed the rye-based diet supplemented with xylanase and ß-glucanase. This is in agreement with the result obtained by Yasar and Forbes (2000), and could be explained by hydrolysis of nonstarch polysaccharides in the rye-based diet by xylanase and ß-glucanase, which diminish their water-holding capacity. Moreover, enzyme supplementation restored the absorptive capacity of the intestinal mucosa by increasing intestinal villi size, and it suppressed early bile acid deconjugation. This is probably due to a decrease in bacteria that hydrolyze conjugated bile acids (Smits and Annison, 1996). In fact, Bedford (2000) reported that the positive effect of adding exogenous enzymes is thought to be related to changes in microflora activity rather than to the direct effect of the enzyme on diet digestibility per se. The relationship between improvement in fat digestibility, decrease in unconjugated bile acids, and addition of xylanase and ß-glucanase has not to our knowledge previously been demonstrated. Despite this beneficial action, fat digestibility was not completely restored to the level observed with the corn-based diet, probably because total bile acid concentrations in intestinal contents remained low. By contrast, protein digestibility was identical to the level observed with the corn-based diet in chickens fed rye supplemented with exogenous enzymes.

	Implications

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The inclusion of rye instead of corn in a broiler chicken diet decreased zootechnical performance and lowered the apparent digestibility of protein and fat. This could be partly due to increased bile acid deconjugation and to partial atrophy of the small intestine wall. The addition of xylanase and ß-glucanase counteracted these effects, reducing the degree of bile acid deconjugation, and increasing villi size. Thus, addition of xylanase and ß-glucanase will lead to an improvement in broiler chicken performance.

	Footnotes

 
¹ The authors wish to thank M. Lessire (INRA, 37380 Nouzilly, France) for diet formulation; G. Kléber (INRA, 37380 Nouzilly, France) for animal care; S. Mallet and M. Leconte (INRA, 37380 Nouzilly, France) for assistance with intestinal content sampling; and C. Gibard and A.-M. Gueugneau (INRA, 78352 Jouy-en-Josas Cedex, France) for their contribution to bile acid analysis.

Received for publication March 6, 2002. Accepted for publication June 26, 2002.

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