Effects of Xylanase in high-co-product diets on nutrient Effects of Xylanase in high-co-product diets on nutrient digestibility in finishing pigs digestibility in finishing pigs

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Effects of Xylanase in High-Co-Product Diets on Nutrient Digestibility in Finishing Pigs1 Introduction Feed ingredients such as wheat midds and DDGS are often used as alternatives to corn and soybean meal in swine diets.The majority of the starch is removed from the kernel of DDGS and midds during the fermentation and milling process of corn and wheat, respectively.The remaining components of the kernel, such as fiber, increase in concentration, which causes most grain co-products to be low in dietary energy.Both DDGS and midds have higher crude fiber content than corn and contain more arabinoxylans.Arabinoxylans are hydrophilic non-starch polysaccharides (NSP) found in grain as minor constituents in the cell wall that act as anti-nutritional factors.Swine do not digest NSP efficiently due to their lack of fiber-specific digestive enzymes; consequently, enzymes like xylanase are viable solutions to increase nutrient availability.
Xylanase is a carbohydrase that is able to break some insoluble bonds that monogastric animals are otherwise unable to digest (Sugimoto and Van Buren, 1970 3 ).Xylanase also has been successful in increasing nutrient digestibility of swine diets (Nortey et  al., 2008 4 ); however, corn is more digestible and lower in fiber than wheat, which is one factor believed to contribute to xylanase's inconsistency in improving growth performance when used in corn-soy-based diets (Jacela et al., 2009 5 ).Xylanase may be more beneficial in corn-soybean meal-based diets when the diets contain high levels of higher-fiber ingredients such as DDGS and midds; therefore, the objective of this study was to evaluate the effect of xylanase in corn-soybean meal-based diets with high co-product inclusion (15% wheat midds and 30, 42.5, or 50% DDGS) on dietary nutrient digestibility.

Procedures
The Institutional Animal Care and Use Committees at Kansas State University and Danisco Animal Nutrition approved the protocol used in this experiment.The study was conducted at the K-State Swine Teaching and Research Farm.Pigs were housed in an environmentally controlled finishing building with pens over a totally slatted floor that provided approximately 10 ft 2 /pig.Each pen was equipped with a dry self-feeder and a nipple waterer to provide ad libitum access to feed and water.The facility was a mechanically ventilated room with a pull-plug manure storage pit.
A total of 18 barrows and 18 gilts (337 × 1050, PIC, Hendersonville, TN; initially 185 lb BW) were individually penned and used in a 14-d experiment.Prior to being assigned to treatment diets, all pigs were fed a corn-soybean meal-based diet with 30% DDGS and 10% midds.All pigs were then assigned to a pen, and treatments were balanced by gender and initial BW and randomly allotted to 1 of 6 dietary treatments with 3 replications per gender (6 replications per treatment).The 6 treatments consisted of corn-soybean meal-based diets with 15% added midds and were arranged in a 2 × 3 factorial with the main effects of xylanase (0 or 4,000 units xylanase per kilogram of diet; Porzyme 93020) and DDGS (Homeland Energy, Lawler, IA; 35%, 42.5%, or 50%).All diets were fed in meal form and manufactured at United Farmers Cooperative (Klossner, MN).In addition, all diets were formulated to contain 1,000 phytase units (FTU)/kg phytase (Table 1).Pigs were allowed ad libitum access to food and water.Diets were formulated to meet all requirements recommended by NRC (1998 6 ).
Feces samples were collected on the morning and night of d 14 via rectal massage from all pigs.All diets contained 0.4% titanium dioxide (TiO 2 ) as the digestibility marker.Samples of feces were stored in a freezer (-4°F) until they were thawed and homogenized for each pig.Fecal samples were dried at 122°F in a forced-air oven, then ground for analysis of bomb calorimetry and TiO 2 concentration.
Gross energy of diets and ground fecal samples were determined with an adiabatic bomb calorimeter (Parr Instruments, Moline, IL).Diets and ground fecal samples were also analyzed for TiO 2 concentration with an atomic absorption spectrometer.
Diet samples were collected from the tops of each feeder and combined for a single composite sample by treatment to measure moisture, CP, crude fat, GE, ADF, NDF, Ca, and P at Eurofins US (Des Moines, IA).Fecal samples were also analyzed for CP, crude fat, GE, ADF, NDF, Ca, and P.
Xylanase activity was analyzed at Eurofins US (Des Moines, IA) in which 1 unit of xylanase activity (XU) is defined as the amount of xylanase that will liberate 0.5 µmol of reducing sugars (expressed as xylose equivalents) from a cross-linked oat spelt xylan substrate (at pH 5.3 and 122°F in 1 min).
Data were analyzed as a 2 × 3 factorial using the PROC MIXED procedure in SAS (SAS Institute, Inc., Cary, NC) with pig as the experimental unit.Linear and quadratic polynomial contrasts were conducted to determine effects of increasing dietary DDGS.Results were considered significant at P ≤ 0.05 and trends at P ≤ 0.10.

Chemical Analysis
Nutrient analyses of the treatment diets were found to be generally similar to formulation (Table 2).The only exception was the Ca level, which was much lower than anticipated in the low-DDGS with xylanase diet.We speculated that limestone was omitted from this diet during manufacturing.The other minor differences were not expected to influence the results of the experiment.
Treatment diets containing xylanase were formulated to contain 4,000 units of xylanase activity per kilogram of diet.Chemical analysis showed some variation in diet xylanase concentrations, but on average, the treatments with the enzyme had significantly higher levels of xylanase activity than those without xylanase, which indicates that xylanase was included in the correct diets.

Nutrient Digestibility
Enzyme × DDGS interactions (P < 0.05) were observed for all nutrient digestibility criteria tested (Table 3).The majority of these interactions were a result of differences in response to increasing DDGS with and without xylanase.In diets with xylanase, apparent digestibility generally decreased as DDGS increased.In diets without xylanase, apparent digestibility decreased as DDGS increased from 35 to 42.5% but increased in diets containing 50% DDGS.Apparent digestibility of NDF decreased (P < 0.01), but digestibility of Ca increased (P < 0.001) with the addition of dietary xylanase; however, Ca digestibility could have been artificially high due to the low level of Ca present in the treatment diet, making pigs more efficient in their utilization of Ca.
Pigs fed diets with increasing DDGS in combination with added xylanase demonstrated reduced (linear, P < 0.02) digestibility of DM, CP, GE, Ca, P, and fat as well as reduced (quadratic, P < 0.01) ADF, NDF, and Zn digestibility; however, when dietary DDGS increased without added xylanase, we observed increased (quadratic, P < 0.05) digestibility of DM, CP, GE, ADF, NDF, and ADF but reduced (quadratic, P < 0.05) apparent fecal digestibility of Ca, P, and Zn (Table 4).This result was driven mainly by the unexplained increase in digestibility when pigs were fed 50% DDGS without the enzyme.
Increasing DDGS regardless of added xylanase also decreased (quadratic, P < 0.01) apparent fecal digestibility of DM, GE, ADF, NDF, and Zn and decreased (linear, P < 0.02) fecal digestibility of fat, Ca, and P (Table 5).In this study, adding dietary xylanase was unsuccessful at improving digestibility in corn-soybean meal-based diets containing fibrous co-products for finishing pigs.

Table 3 .
Effect of dietary xylanase and dried distillers grains with solubles (DDGS) on finishing pig apparent total tract digestibility 1

Table 5 .
Effects of dietary xylanase and DDGS on finishing pig apparent total tract digestibility 1