- Open Access
Effects of an enzyme complex on in vitro dry matter digestibility of feed ingredients for pigs
© Kong et al. 2015
- Received: 14 January 2015
- Accepted: 26 May 2015
- Published: 17 June 2015
Feed ingredients of plant origin are commonly used in swine diets. However, the major components of plant cell walls, non-starch polysaccharides (NSPs), reduce nutrient digestibility. To improve the efficiency of feed utilization, exogenous enzyme products that degrade NSPs have been widely used in commercial animal feeds. Nonetheless, the effects of exogenous enzyme addition to swine diets on nutrient digestibility have not been determined. To this end, in vitro approaches may be used. The objective of this study was to determine the effects of an enzyme complex (EC) containing xylanase, protease, and phytase on the in vitro dry matter (DM) digestibility of nine feed ingredients including cereal grain energy sources (corn, wheat, and barley) and protein sources (soybean meal, rapeseed meal, palm kernel meal, cottonseed meal, copra meal, and distillers dried grains with solubles). Both in vitro ileal and total tract digestibility (IVID and IVTTD, respectively) of DM were determined for the nine test ingredients, with or without EC addition. The EC addition increased the IVID of DM in copra meal (p = 0.047) and tended to increase the IVID of DM in corn, wheat, barley, palm kernel meal, cottonseed meal, and DDGS (p < 0.10). On the other hand, no significant effect was observed in soybean meal and rapeseed meal. The IVTTD of DM in the test ingredients was not affected by the addition of EC, except for cottonseed meal (52.1 vs. 50.6%, p = 0.053). In conclusion, the effects of EC addition on in vitro DM digestibility may vary, depending on the test ingredient and method used.
- In vitro dry matter digestibility
- Non-starch polysaccharide
Feedstuffs of plant origin are widely used in swine diets. However, the major components of plant cell walls, non-starch polysaccharides (NSPs), have anti-nutritive effects on nutrient digestibility. Arabinoxylan, a cell wall NSP consisting of arabinose and xylose (Saulnier et al. 2012), is the most common pentosan in cereal grains such as corn, wheat, and barley (Masey O’Neill et al. 2014). The use of exogenous enzymes in swine diets is a common strategy to ameliorate anti-nutritive effects of NSPs on nutrient utilization. Amongst these, xylanase and glucanase are dominant NSP-hydrolyzing enzymes in swine feeds and their effects have been extensively studied (Adeola and Cowieson 2011). Furthermore, because phytates are generally concentrated in fibrous cell wall in a practical swine diet, a cocktail of multi-carbohydrase and phytase was also proposed to improve nutrient digestibility of pigs (Kiarie et al. 2010).
In vitro digestibility methods that simulate the gastrointestinal condition of pigs have been used to predict the apparent ileal and total tract digestibility of nutrients in various feedstuffs (Boisen and Fernández 1995, 1997; Regmi et al. 2009; Park et al. 2012; Cervantes-Pahm et al. 2013), and to test the efficacy of mycotoxin sequestering agents (Kong et al. 2014). It is therefore possible that this approach can be similarly applied to determine the efficacy of exogenous enzyme addition to swine diets on nutrient digestibility. However, these methods have not been evaluated for estimating digestibility of nutrients in swine feed or ingredients containing exogenous enzymes. Therefore, the objective of the present study was to determine the efficacy of an enzyme complex (EC) containing xylanase, protease, and phytase, on in vitro ileal and total tract digestibility (IVID and IVTTD, respectively) of dry matter (DM) in ingredients for pigs.
Enzyme complex and test ingredients
The EC contained a combination of Aspergillus niger-derived xylanase, protease and phytase at 100, 700 and 300 units/g of complex, respectively. Nine feed ingredients were used for in vitro DM digestibility. These included corn, wheat, and barley as energy sources, and soybean meal, rapeseed meal, palm kernel meal, cottonseed meal, copra meal, and distillers dried grains with solubles (DDGS) as protein sources.
Before the analyses, ingredients were finely ground and each ingredient was divided into two groups. Each group was supplemented with either EC or wheat bran at 1.0%. After mixing, three ingredient samples from each group were weighed for in vitro DM digestibility analyses.
In vitro digestibility procedures
In vitro procedures were modified from a two-step IVID (Boisen and Fernández 1995) or three-step IVTTD (Boisen and Fernández 1997) procedures. In the first step of the IVID procedure, 1 g of ground ingredient sample was transferred into 100-mL conical flasks and 25 mL of sodium phosphate buffer solution (0.1 M, pH 6.0), and 10 mL of HCl (0.2 M, pH 0.7) were added. To simulate digestion conditions in the stomach, 1 M HCl or NaOH was used to adjust the pH to 2.0, and 1 mL of freshly prepared pepsin solution (10 mg/mL; ≥250 units/mg solid, P7000, Pepsin from porcine gastric mucosa, Sigma-Aldrich, St. Louis, MO, USA) was added to the samples. To avoid bacterial contamination, 0.5 mL of chloramphenicol (C0378, Chloramphenicol, Sigma-Aldrich, St. Louis, MO, USA) solution (5 g/L ethanol) was also added. Test flasks were closed with a silicon stopper and incubated in a shaking incubator at 39°C for 6 h.
After incubation, the second step of the procedure simulated the digestion in the small intestine. Firstly, 10 mL of sodium phosphate buffer solution (0.2 M, pH 6.8) and 5 mL of NaOH (0.6 M, pH 13.8) were added to the samples. Then, pH was adjusted to 6.8 using 1 M HCl or NaOH. Thereafter, 1 mL of freshly prepared pancreatin solution (50 mg/mL; 4 × USP, P1750, Pancreatin from porcine pancreas, Sigma-Aldrich, St. Louis, MO, USA) was added. After incubation in a shaking incubator at 39°C for 18 h, 5 mL of 20% sulfosalicylic acid solution was added and samples were left for 30 min at room temperature to precipitate the indigestible protein. The samples were then filtered through pre-dried and -weighed glass filter crucibles (Filter Crucibles CFE Por. 2, Robu, Hattert, Germany) containing 400 mg of Celite using the Fibertec System (Fibertec System 1021 Cold Extractor, Tecator, Hӧganӓs, Sweden). Test flasks were rinsed twice with 1% sulfosalicylic acid solution, and 10 mL of 95% ethanol and 99.5% acetone were added twice to the glass filter crucibles. Glass filter crucibles with undigested residues were dried at 130°C for 6 h.
The procedure for IVTTD consisted of three-steps. The first and second steps were similar to the IVID procedure, except for the weight of the samples, concentration of the enzymes, and incubation time. For IVTTD, 0.5 g of ingredient sample was used, and the concentrations of pepsin and pancreatin solutions were increased to 25 and 100 mg/mL, while the incubation times were reduced to 2 and 4 h, respectively. In the third step of the IVTTD procedure, 10 mL of 0.2 M EDTA solution was added to the samples. The pH was then adjusted to 4.8 by adding acetic acid 30% or 1 M NaOH. Samples were supplemented with 0.5 mL of multi-enzyme (V2010, Viscozyme® L, Sigma-Aldrich, St. Louis, MO, USA) as a substitute for microbial enzymes, and incubated in a shaking incubator for 18 h at 39°C. After incubation, the undigested residues were collected and dried as previously described in the IVID procedure.
Calculations and statistical analyses
Data were analyzed by MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, USA). The model included EC addition as a fixed variable. Differences between least squares means were determined by the PDIFF option with the Tukey’s adjustment. The significance and tendency of treatment effects were declared at p < 0.05 and 0.05 ≤ p < 0.10, respectively.
In vitro ileal digestibility of dry matter in test ingredients, with or without the addition of an enzyme complex
Ileal digestibility, %
Enzyme complex additiona
Palm kernel meal
In vitro total tract digestibility of dry matter in test ingredients, with or without the addition of an enzyme complex
Total tract digestibility, %
Enzyme complex additiona
Palm kernel meal
In conclusion, the effects of EC addition on the IVID or IVTTD of DM may vary, depending on the test ingredient and method used.
CK: Wrote most of the manuscript and contributed to the calculation and analysis of the data. CSP: Designed and performed experiments. BGK: Supervised the experimental work and manuscript preparation. All authors read and approved the final manuscript.
The present manuscript is based on research supported in part by the Rural Development Administration (Republic of Korea; PJ009340). This paper was supported by the KU Research Professor Program of Konkuk University.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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