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Enzyme Practical

Enzymes in wheat-based diets

For diets based on either wheat or barley, improvements in energy digestibility, growth performance or voluntary feed intake have been achieved often but not consistently using supplemental enzymes. As indicated in Figure 1, more opportunities exist with wheat and barley to improve digestibility of crude fiber and therefore energy digestibility using supplemental enzymes or other feed processing technologies such as particle size reduction.

Arabinoxylans or xylans are the main NSP in wheat that limit energy digestibility in swine (Zijlstra et al. 1999). Logically, xylanase is an enzyme used for wheat diets to improve energy digestibility. Energy digestibility might also be improved using particle size reduction; by grinding the wheat more finely, the relative surface area of the ground particles increases and nutrient digestibility might be improved. The combination of xylanase supplementation and particle size reduction was studied in wheat-based diets (Tortora,2002,35). Particle size reduction improved feed efficiency linearly, but xylanase supplementation did not affect feed efficiency or dry matter digestibility. In a accompanying study with finisher pigs, xylanase supplementation tended to improve nutrient digestibility and reduced feed intake while growth performance was maintained.

Wheat samples can have a wide range in total xylan content, and this wide range is inversely related to energy digestibility . The wheat sample that is included is the diet can thus affect the chance of observing a beneficial effect of xylanase supplementation. Indeed, in recent experiments in our laboratory, the beneficial effect of xylanase supplementation and particle size reduction depended on the wheat sample that was included in the test diet, similar to previous experiments conducted with barley differing in NSP profile (Tortora,2002,35). The latter indicates that feed evaluation and processing decision should be integrated to maximize the beneficial effects of enzyme supplementation or particle size reduction.

Practical application

Two diet formulation methods exists to apply enzyme treatments in practice: (1) formulate diets to a regular nutrient content and supplement with an enzyme, while hoping for an improvement in feed efficiency, or (2) formulate diets to a reduced nutrient content and count on an uplift by the enzyme to a regular nutrient content, while reducing feed costs. In most experiments including the experiment discussed in the proceedings, enzymes are included in the diet as a top dress: diets are formulated to meet the nutrient requirement. A second approach is to include enzymes in the diet to deal with the expected variation in ingredient quality. Hopefully in the future, rapid screening of ingredient samples will allow to match the substrate with the enzyme and allow the enzyme dose to be adjusted depending on the substrate content in the ingredient or complete diet.(Wilmore,2008)

Conclusion

Feed ingredients have a range in content of energy-providing macronutrients. Especially digestibility of the crude fiber fraction has a large range in nutrient digestibility among feed ingredients. The range in fiber digestibility is directly related and inversely related to a range in digestibility of energy, the most expensive nutrient contained in swine ...