XYLANASE IMPROVES THE ILEAL ENERGY AND NITROGEN
DIGESTIBILITY OF HIGH WHEAT FINISHER DIETS IN SWINE

 

S.C. Wolford, P.H. Simmins[1], and T. van Kempen

 

Summary

The ileal digestibility of a high wheat/wheat shorts diet was improved with the addition of xylanase, and as a result, ileal indigestible energy and nitrogen were reduced by 1.2% for each unit of enzyme added to a gram of feed. Xylanase thus improves the utilization of feed while potentially reducing waste and odor.

 

Introduction

The use of enzymes in poultry diets is well established. Beta glucanases are commonly used in diets containing barley and rye, while xylanases are commonly used in diets containing wheat. These enzymes improve the energy and protein digestion of such diets, and can also improve gut health.

 

Although digestive physiology would dictate that the effects of enzymes should be similar in pigs, experiments have yielded rather controversial effects. In some cases, enzymes did not improve the nutritional value of cereal containing diets, while in others, a clear benefit was seen. Possible reasons for not seeing effects in some experiments may be that the experiments were not designed properly. For example, were enough animals used to detect differences in digestibility in line with expectations (1 to 3 percent improvements), or was the right response parameter measured (fecal digestibility is confounded by fermentation in the large intestines).

 

Growth performance experiments in pigs pose even greater challenges than those in poultry since intake is dictated by digestible energy content for the former, rather than by digestive capacity as is true for the latter. Thus, with pigs, enzymes can be expected to slightly reduce feed intake and slightly improve performance although to a degree that is difficult to demonstrate statistically. Growth performance is also much more variable in pigs and, typically, fewer animals are used than in poultry experiments.

The objective of this experiment was to evaluate the effect of xylanase on ileal digestibility using sufficient animals to detect digestibility differences of 2%. Ileal digestibility is the most appropriate parameter to monitor due to its sensitivity and due to the absence of confounding effects of lower bowel fermentation.

 

Materials and Methods

Animals and Diets. Eleven barrows were surgically fitted with canulas at the distal ileum. Following a recovery period, nine of the cannulated pigs were used in a 9 x8 Youden square designed experiment. Water was provided ad libitum, and feed allowance for each period was calculated at 45 g · kg^-0.75 BW · meal^-1, with meals provided at 12 h intervals.

 

Three wheat-based diets were formulated that contained 10, 20, or 30% wheat shorts (Table 1 and 2). To these diets, xylanase was added at 0, 4, or 7 units of xylanase per gram of feed. Chromic oxide (0.3%) was added as an indigestible marker and was used to calculate the digestibility values. Diets were formulated following guidelines from Prairie Swine Centre on an equal ileal digestible amino acid to net energy basis.

Table 1. Ingredient content of the experimental diets.

 

 

Table 2. Calculated composition of the experimental diets.

 

 

Each experimental 7-d period consisted of a 5-d adaptation and a 2-d collection period. Digesta collection was started immediately after the morning feeding and terminated at the beginning of the evening feeding. Ileal digesta were collected continuously from the cannula into an attached Nalgene bottle and transferred hourly to a freezer where they were pooled by pig within each period.

 

Chemical Analyses. The N, P, Cr, and amino acid analyses of freeze-dried samples were conducted by the Experimental Station Chemical Laboratories, University of Missouri, Columbia. Amino acid analysis (AOAC 1995) was only performed on samples obtained with the high and low wheat short levels. Energy was determined after oven drying at 60°C using an oxygen bomb calorimeter (IKA Model C5000, IKA, Wilmington, NC).

 

Calculation. Apparent digestibility coefficients were calculated using the following equation:

 

Apparent digestibility, % = 100- ((C_d · N_I )/(N_d · C_I )) · 100    where:

 

C_d = Chromium concentration in the diet (mg/kg)

N_I = Nutrient concentration in ileal digesta (%)

N_d = Nutrient concentration in the diet (%)

C_I = Chromium concentration in the ileal digesta (mg/kg)

 

Statistical Analyses. All data were analyzed using the GLM procedure of SPSS 10.0 (SPSS Inc., Chicago, IL). Wheat shorts level, enzyme level, and their interactions were first tested as discrete variables. This test revealed that the interaction was not statistically significant and that a linear response was observed for enzyme level. Therefore, the final model contained wheat short level as a discrete variable, enzyme level as a continuous variable, diet, animal, and period. Results listed obtained with this model are based on unconditional analyses.

 

Results and Discussion

Effect of wheat shorts level on the digestibility. Increasing wheat shorts from 10 to 20% resulted in a small, numerical decrease (1%) in energy digestibility (Table 3).  Increasing wheat shorts to 30% resulted in a significant decrease in energy digestibility as compared to 20% and 10% (3.2 and 4.2% decrease in energy digestibility, respectively).

 

Wheat shorts inclusion had no clear effect on nitrogen digestibility. The effects on amino acid digestibility were only evaluated for the 10% and 30% wheat shorts level. In line with the results for nitrogen, there was no significant effect of wheat shorts level on amino acid digestibility for most of the amino acids, although small numerical decreases were observed. The exceptions were lysine and threonine, for which decreases in digestibility of 1.13±0.56% (p=0.05) and 2.03±0.90% (p<0.05) were observed, respectively.

 

Pigs fed diets containing 20% or 30% wheat shorts had a significantly lower phosphorus digestibility than the diet containing 10% wheat shorts.

 

Table 3. Digestibility of nitrogen, energy, and phosphorus as affected by wheat shorts level.

 

 

Effect of xylanase level on the digestibility of energy, nitrogen, phosphorus, and amino acids. The effect of xylanase on digestibility was evaluated for energy, nitrogen, and phosphorus in all three levels of wheat shorts, and for amino acids in only the low and high level of wheat shorts. Based on all three levels of wheat shorts, xylanase improved digestibility of energy by 0.37±0.09% (p<0.05), nitrogen by 0.22±0.08 (p<0.05), and phosphorus by 0.23±0.22% (ns), all per unit of enzyme added per gram of feed. Thus, for the 4 IU enzyme/g feed dose, energy digestibility improved 1.49±0.37%, and for the 7 IU enzyme /g feed dose, 2.61±0.64%.

 

The effects of enzyme on the high and low wheat shorts level is shown in Figure 1. For energy (0.48±0.15%) and nitrogen (0.26±0.11%) digestibility, the increase in digestibility observed was similar to that observed using all three levels of wheat shorts, while for phosphorus a larger, significant improvement in digestibility was observed (0.62±0.29%). This improvement, however, was not different from that observed with all three levels of wheat shorts.

 

For amino acids, digestibility improved for all essential amino acids except arginine, cysteine, and tryptophan (Figure 1). The improvement averaged 0.28% per unit of enzyme/g feed, thus similar to the improvement observed for nitrogen.

 

The response for the different parameters was quite variable (excluding phosphorus), with the largest improvement being 3.7 times larger (energy) than the smallest (arginine). Expressing the enzyme effect as a decrease in indigestibility (improvement/(100-digestibility of control)*100, Figure 1) resulted in a much more homogeneous response, with the largest increase (histidine) being only 1.8 times the smallest (nitrogen).

 

 

Figure 1. Improvement in digestibility and decrease in indigestibility (per unit of enzyme added per gram of feed) for energy (E), nitrogen (N), phosphorus (P), and all the essential amino acids.

 

Wheat shorts are a high fiber byproduct from the wheat processing industry. Increasing the level of wheat shorts in the diet from 10 to 30% resulted in a decrease in energy digestibility. From 10 to 20%, this decrease was only numerical (1%), but from 20 to 30% this decrease was significant (3.2%).

 

Xylanase improved the digestibility of energy and nitrogen independent of the level of wheat shorts in the diet. This improvement was linear for the three levels of enzyme tested (0, 4, and 7 IU/g feed), with an improvement in digestibility of 0.37±0.09% for energy and 0.22±0.08% for energy per unit of enzyme per gram of feed. Thus, when using 7 IU of enzyme per gram of feed improvements in digestibility of 2.61% for energy and 1.56% for nitrogen can be expected.

Amino acid digestibility was only evaluated in the low and high wheat shorts diets, and in those two groups, xylanase improved nitrogen digestibility by 0.26±0.11% per unit enzyme per gram feed. The response for individual essential amino acids was similar: lysine digestibility improved 0.29±0.10%, methionine digestibility improved 0.24±0.11%, and threonine digestibility improved 0.41±0.16%. This last improvement was the largest observed within the essential amino acids. In contrast, no significant increase in arginine digestibility was observed (0.13±0.11%), even though the standard error was in line with that for other amino acids (no significant responses for cysteine and tryptophan were observed either, but the data suggest that this is due to excessive variation, probably as a result of assay problems for those amino acids). Interestingly, arginine was the most digestible amino acid overall, while threonine was the least digestible (based on apparent digestibility), suggesting that the response observed was more closely related to the decrease in indigestibility than the increase in digestibility. Indeed, when expressing the enzyme response as a decrease in indigestibility, a response was observed that was statistically the same for all parameters and much more uniform numerically (see Figure 1).

Reducing indigestibility with enzymes is intuitively more appropriate than improving digestibility, but it may be a reason why others have failed to show effects of enzymes. In diets that already have a low indigestible fraction (like arginine in this experiment), it is more difficult to show an enzyme response as a smaller response can be expected (less room for improvement). Diets with a poor digestibility (like threonine in this experiment) are more likely to show an enzyme response.

 

Implications

Xylanase is effective at improving digestibility and thus, reducing the excretion of nutrients in swine manure.