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Poult Sci 2007. 86:2350-2357. doi:10.3382/ps.2007-00115
© 2007 Poultry Science Association
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METABOLISM AND NUTRITION

The Effect of Phytase and Glucanase on the Ileal Digestible Energy of Corn and Soybean Meal Fed to Broilers

M. A. Leslie*, E. T. Moran, Jr.*,1 and M. R. Bedford{dagger}

* Department of Poultry Science, Auburn University, Auburn, AL 36849; and {dagger} Syngenta Animal Nutrition, Chestnut House, Beckhampton, United Kingdom SN8 1QJ

1 Corresponding author: emoran{at}acesag.auburn.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The current research was designed to determine the effect of phytase and glucanase on the energy value of corn and soybean meal (SBM) separately for broilers at various ages. The treatments were arranged as a 2 x 2 x 2 factorial, with 0 or 500 phytase units/kg or with 0 or 500 units of glucanase/kg, supplemented to either corn or SBM, with each combination represented by 6 cages of 10 birds. Diets of pure corn and soybean meal were not supplemented with additional nutrients, and were fed for 3-d periods beginning at 7, 14, or 21 d of age, representing the immature, transitional, and mature digestive tract, respectively. Each experiment was performed on a different group of birds from the same hatch. At the end of each experimental period, the broilers were euthanized and the contents of the ileum, duodenum and jejunum (pooled), and pancreas were removed for analysis. The ileal samples were analyzed for acid-insoluble ash and gross energy to determine the ileal-digestible energy (IDE) of the feedstuffs. The pancreas and duodenal-jejunal samples were analyzed for proteolytic and amylase activity to determine the influence of practical levels of phytate on enzyme activity. Results showed that neither phytase nor glucanase influenced enzyme activity in the digesta or pancreas, suggesting that practical levels of phytate did not influence the activity of proteolytic enzymes or amylase. Phytase did not influence the IDE value of either corn or SBM, and improved DM digestibility of the feed only for corn fed at 21 to 23 d. Glucanase improved IDE in both the corn and SBM diets at all ages, and improved DM digestibility in corn diets at all ages and SBM diets fed at 14 to 16 d. The IDE and DM digestibility of corn and the digesta and pancreatic enzyme activities increased with age, whereas the IDE of SBM was similar among age groups. The relative effect of glucanase on IDE of both feedstuffs was similar among age groups.

Key Words: phytase • glucanase • corn • soybean meal


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Exogenous enzymes are added to poultry diets to manipulate conditions in the digestive tract and improve the nutrient value of feedstuffs (Classen, 1996; Meng et al., 2005). Numerous studies on the effects of phytase have shown that the enzyme increases phosphorus availability by hydrolyzing phytate and also increases mineral and protein solubility, thus improving protein digestibility (Sebastian et al., 1996; Igbasan et al., 2001; Kies et al., 2001; Shirley and Edwards, 2003; Onyango et al., 2005), whereas others have shown no effect (Augspurger and Baker, 2004; Oduguwa et al., 2007). In wheat and barley diets, phytate hydrolysis also increases AME values (Ravindran et al., 2000, 2001; Kies et al., 2001). Fibrolytic enzymes have been used extensively in wheat- and barley-based diets to reduce viscosity in the small intestine through the cleavage of soluble nonstarch polysaccharides. Additionally, these enzymes degrade cell walls and increase the digestibility and absorption of sugars from hemicellulose (Meng et al., 2005). In doing so, substrates (i.e., starch) within cell walls become available for degradation by endogenous enzymes (Classen, 1996). To date, research on these enzymes has not extensively examined their effect on corn or soybean meal (SBM) individually. Moreover, the potential for different responses based on the age and physiological development of the digestive tract is often ignored.

The effect of commercially available enzymes on the feeding value of major ingredients is often based on their effect in young chicks less than 2 wk of age (Murakami et al., 1994; 1995; Meng and Slominski, 2005) or prime-age roosters (Yaghobfar and Boldaji, 2002), with some more recent trials performed in growing birds (Cowieson et al., 2006; Yamazaki et al., 2007). In newly hatched chicks, the enterocyte is poorly developed, limiting the bird’s digestion and absorption abilities (Iji et al., 2001a,b,c). During this maturation period, the gut lacks the competency to fully digest feedstuffs and absorb smaller molecules because of a lack of brush-border enzymes, inadequate maintenance of absorptive mechanisms, and low surface area caused by immature villus height (Van Leeuwen et al., 2004). As the gastrointestinal tract develops, it is able to take advantage of the effects of fibrolytic enzymes. Before this, however, the pancreatic enzymes needed to initiate digestion in the intestinal lumen are limited in both volume and activity (Noy and Sklan, 1995). Thus, they may be unable to utilize substrates made available by a fibrolytic enzyme. In addition, phytate has been shown to reduce both amylase and trypsin activity in vitro (Deshpande and Cheryan, 1984; Thompson and Yoon, 1984; Knuckles and Betschart, 1987). In vivo studies have not yet been performed.

The objectives of this experiment were to determine the influence of phytase and glucanase on the energy digestibility of corn and SBM independently and to investigate the effect of age on the response to these enzymes. To minimize the influence of cecal microflora, ileal digestibility was used to quantify energy availability. As an indirect test of the effect of phytate on endogenous enzyme activity, digesta and pancreatic enzyme levels were also determined.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Experimental Design
All procedures were reviewed and approved by the Auburn University Institutional Animal Care and Use Committee. A population of 1-d-old male Ross x Ross 308 broiler chicks was obtained from a commercial hatchery (Wayne Farms Hatchery, Troy, AL). The chicks were housed in battery cages in 3 rooms (48 cages per room) and provided a standard corn-soybean meal diet and water for ad libitum consumption. Each room represented a different age at which the experiment would start, with chicks in one room fed the experimental rations from 7 to 9 d, another from 14 to 16 d, and the third from 21 to 23 d. All birds received a commercial-type complete starter diet (Table 1Go) until the initiation of the experiment.


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  		Table 1. Composition of the starter diet and corn and soybean meal treatments
 
The experimental treatments consisted of either pure corn or SBM plus 1% Celite (Fisher Scientific, Fair Lawn, NJ), an acid-insoluble ash marker (Table 1Go), supplemented with 0 or 500 of phytase units, and 0 or 500 units of glucanase/kg of treatment. The phytase (EC 3.1.3.2 [EC] 6) was derived from Escherichia coli and evolved by using gene site saturation mutagenesis (Palackal et al., 2004) to produce an enzyme with greater thermotolerance than the wild type. The enzyme was expressed in Pichia pastoris. The glucanase (EC 3.2.1.6) was derived from a sample of bovine manure and cloned into and expressed in E. coli. The sequencing that has been conducted suggests it is of Bacillus origin. Glucanase activity was determined as described by Miller (1959) and expressed in DNS units. Each feedstuff was mixed with Celite, pelleted, and crumbled. The activity of each enzyme preparation was determined prior to mixing the feed, and the appropriate amount of each preparation was measured to 2 decimal places (0.01 g) to achieve accurate enzyme levels. Measurement of activity in the complete feed was not performed because of potential interference of enzymes and compounds in the feedstuff and inaccuracies associated with assays at low concentration. Enzymes were mixed into the crumbled mixture of the test feedstuff and marker after heat processing to prevent loss of enzyme activity caused by pelleting.

The procedure performed was the same for each of the age ranges tested. Eight hours prior to the onset of each experimental period, birds were weighed and feed was withdrawn. Birds were then fed the experimental diets for 48 h, weighed, and euthanized via asphyxiation with CO2 gas. The pancreas and the contents of the duodenum and jejunum (pooled) and the ileum were removed and immediately frozen at – 20° C for subsequent analysis. The duodenum-jejunum was defined as the portion of the small intestine between the gizzard and the junction of the residual yolk sac, and the ileum was defined as the small intestine between the attachment of the residual yolk sac and the ileocecal junction. Duodenum-jejunum and pancreas samples were homogenized in phosphate buffer (0.1 M, containing 0.157 g of KH2PO4 and 1.575 g of Na2HPO4 · 2H2O diluted to 100 mL, pH 7.6) and centrifuged at 1,435 x g for enzymatic analysis. Ileal samples were freeze-dried, ground, and analyzed for acid-insoluble ash content (Scott and Hall, 1998) and gross energy content (Parr 6300 Calorimeter, Parr Instrument Company, Moline, IL).

Enzyme Analysis
Pancreatic samples and duodenal-jejunal contents were analyzed for amylase activity (Rick and Stegbauer, 1974), proteolytic activity (Rick, 1974), and protein content (Bradford, 1976). Briefly, to determine amylase activity, 3 µL of homogenate was combined in a test tube with phosphate buffer (pH 6.9) and a solution of potato starch (1% starch, wt/vol) and incubated at 35° C for 10 min. A solution containing 3,5-dinitrosalysilic acid was added to the test tube and incubated again at 100° C for 5 min to stop the reaction. After the samples cooled, the absorbance was read with a spectrophotometer (Model UV-1601 ultraviolet-visible spectrophotometer, Shimadzu Corp., Kyoto, Japan) at 246 nm and compared against a maltose standard curve.

Proteolytic activity was determined by using casein as a substrate (Rick, 1974). Three microliters of homogenate was incubated in a phosphate buffer (0.1 M, containing 0.157 g of KH2PO4 and 1.575 g of Na2HPO4 · 2H2O diluted to 100 mL, pH 7.6) with 1 mL of 0.5% casein at 35° C for 10 min. The reaction was stopped by adding 3 mL of 5% trichloroacetic acid to precipitate all protein in the solution. Samples were centrifuged for 10 min at 25,137 x g. The supernatant was removed and absorbance was read on a spectrophotometer at 540 nm. Samples were compared against a standard curve generated by using porcine trypsin of known activity.

The amount of protein in the homogenate was determined by using the Coomassie dye-binding procedure (Coomassie Bradford Protein Assay Kit, Pierce, Rockford IL). Briefly, 3 µL of homogenate was mixed with Coomassie dye, allowed to equilibrate, and read at an absorbance of 595 nm. The samples were compared against a known standard of bovine albumen. Amylase and proteolytic activities were then expressed as units of activity per milligram of protein in the sample.

Statistical Analysis
All measurements were taken by using the pen as the experimental unit. Data were analyzed as 2-way ANOVA by using the GLM procedure of SAS (SAS Institute, 2001), with phytase and glucanase levels as main effects, and with corn and SBM treatments analyzed separately. Tukey’s multiple range test was used to separate treatment means at P < 0.05.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Feedstuffs used in these experiments were not supplemented with calcium, phosphorus, microminerals or vitamins, and were not balanced for protein or energy. Therefore, interpretation of the live performance data was of limited value. The assumption was that the short timeline of the trial would prevent any symptoms of deficiency from interfering with the results (Sullivan et al., 1974; Ceccarelli et al., 1975; Barrett and Keely, 2000). Minerals essential to enzyme function (e.g., calcium and chloride for amylase activity) and the digestive tract (e.g., sodium for active transport) were believed to be of sufficient quantity, both in the feedstuffs and endogenously, to maintain normal enzyme and absorptive function (Sullivan et al., 1974; Ceccarelli et al., 1975; Barrett and Keely, 2000).

The digestible energy and DM digestibility of corn and SBM are presented in Tables 2Go and 3Go, respectively. From 7 to 9 and 14 to 16 d of age, neither feedstuff was influenced by phytase supplementation. These results agree with previous experiments showing that phytase does not affect AME in corn-SBM diets. Between 21 and 23 d of age, the DM digestibility of corn was 78.5%, and with phytase it increased to 79.3%. These results agree with those found in wheat-based, but not corn-based, diets. In wheat-based diets, phytate is thought to be integrated into the cell wall (Frolich, 1990), and as it is degraded, holes are left in that wall through which endogenous enzymes can enter (Classen, 1996). This results in degradation of encapsulated substrates, improving DM digestibility and AME. In corn, there is no evidence that phytate is incorporated into cell walls, and no similar effect would be expected.


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  		Table 2. Ileal digestible energy (IDE) and DM digestibility of corn supplemented with phytase and glucanase
 

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  		Table 3. Ileal digestible energy (IDE) and DM digestibility values of soybean meal supplemented with phytase and glucanase
 
Glucanase increased both the digestibility of corn and the ileal digestible energy (IDE) of both corn and SBM at all 3 ages tested (Tables 2Go and 3Go). The degree of improvement in IDE caused by glucanase supplementation was similar across all age groups and was similar between feedstuffs. An increase in the IDE value of corn with increasing age was also seen, whereas no comparable increase was noted for SBM. The immature gastrointestinal tract of young chickens is characterized by a small and unstable microbial population and low endogenous enzyme activity (Iji et al., 2001a). As the digestive tract develops, endogenous enzyme activity increases (Noy and Sklan, 1995). However, fiber digestion remains insubstantial because a stable microflora is yet to be established (Josefiak et al., 2004). Because the chicken is unable to digest and utilize many of the complex carbohydrates found in SBM, its ability to utilize energy from the feed-stuff may increase with a stable microflora, whereas enzyme activities have little influence. Because the measurements discussed here were taken in the ileum, the largest portion of the microfloral influence was omitted. However, microbial populations in the crop and small intestine may contribute to fiber digestion in older birds. The main source of energy in corn is from starch, so increases in amylase activity are likely responsible for the increase in IDE over time.

The effect of glucanase on the IDE value of corn was likely due to an increase in amylase access to starch granules within the cells of the endosperm. Fibrolytic enzymes are thought to degrade portions of the cell wall, allowing endogenous enzymes to have access to the cell contents. The mode of action of glucanase on SBM is less obvious because of differences in the fiber structure and starch content of the feedstuff. The glucanase used in this experiment has a low substrate specificity, and may contribute to the degradation of hemicelluloses other than glucans.

Results for corn diets showed that phytase had no effect on the activity of either proteases or amylase in the digesta or pancreas (Tables 4Go and 5Go), suggesting that any effect phytate may have on amylase or proteolytic enzymes is indirect, through interference with the substrate. In SBM diets, phytase supplementation increased the activity of pancreatic proteases at 7 to 9 and 14 to 16 d (Table 6Go) and the activity of digesta amylase at 21 to 23 d (Table 7Go). The data also showed that the activity of those enzymes was highly variable, because the SEM values were as high as 20% of the mean. Pancreatic enzyme activity was particularly variable. Comparisons in activity between corn and SBM diets were not made because the activities were expressed on a unit protein basis.


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  		Table 4. Amount of {alpha}-amylase1 in the duodenal-jejunal contents (digesta) and pancreas of broilers fed corn supplemented with phytase and glucanase
 

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  		Table 5. The amount of protease activity1 in the duodenal-jejunal contents (digesta) and pancreas of broilers fed corn supplemented with phytase and glucanase
 

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  		Table 6. Amount of protease activity1 in the duodenal-jejunal contents (digesta) and pancreas of broilers fed soybean meal supplemented with phytase and glucanase
 

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  		Table 7. The amount of {alpha}-amylase1 in the duodenal-jejunal contents (digesta) and pancreas of broilers fed soybean meal supplemented with phytase and glucanase
 
In the current study, if the presence of phytate in the intestinal lumen reduced amylase or trypsin activity, the hypothesized result was decreased activity in the digesta, coinciding with increased pancreatic activity to compensate (Nitsan and Madar, 1978; Simoes-Nunes and Corring, 1979). The supplementation of phytase would be expected to alleviate these responses. Because the activity of both enzymes was measured in vitro by using a substrate that was not exposed to phytate in the digestive tract, this experiment would only detect differences if the phytate molecule interfered directly with the enzyme.

In vitro studies have shown that the presence of phytate reduces the activity of both amylase and proteases, notably trypsin (Singh and Krikorian, 1982; Deshpande and Cheryan, 1984; Thompson and Yoon, 1984; Knuckles and Betschart, 1987). One potential mechanism of this interference is thought to be precipitation of a complex made up of calcium, phytate, and the enzyme (Deshpande and Cheryan, 1984; Knuckles and Betschart, 1987), thus removing the enzyme from potential interaction with its substrate. The results of this experiment suggest that precipitation of this complex does not occur at a rate high enough to affect enzyme activity in the lumen.

The aim of this study was to determine the effects of phytase and glucanase individually on energy utilization and amylase and protease activities in corn and SBM. Although there was no effect of phytase on digestible energy, glucanase improved the energy value of both corn and SBM at all ages. The response of corn to glucanase supplementation was highest between 14 and 16 d of age, whereas the greatest response with SBM was seen at 21 to 23 d of age. These data suggest that the age-related competency of the digestive tract must be taken into account when assessing the energy value of fibrolytic enzymes in poultry feed.

Received for publication March 15, 2007. Accepted for publication July 31, 2007.


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 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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