Questions

Enzymes are proteins and subject to the rigours of a digestive system designed to break down feed proteins, hence are themselves digested. Prior to loss of activity, they must accomplish the degradation of the target substrate. A critical component is pH, enzymes do not function outside their preferred pH range, and will lose activity progressively outside this range. Food entering the anterior digestive tract (crop, proventriculus, ventriculus in chickens, stomach in pigs) will initially be mildly acidic and near optimum for fungal enzymes (5.0-5.5). The pH declines as the ingested feed is acidified with gastric secretion (HCl) with activity declining, ultimately reaching a point where activity is irreversibly lost. Only a fraction of the enzyme will survive passage to the small intestine. GNC enzyme activities are determined at pH 4.0 to simulate this process.

All GNC products are based on traditional fungal systems. GNC Bioferm achieves high activity levels without relying on GMO technology. The advantage conferred by GMO technology is the capacity to achieve very high levels of specific enzymes, for example, genetically engineered phytase has been instrumental in its adaptation for feed applications. In the case of complex NSP degradations, as a single enzyme GMO products lack the ancillary enzymes and co-factors to effectively function across feed ingredients. A further disadvantage is that GMO products are typically a single isozyme which only function within a narrow band of the pH spectrum, unlike natural products which will function over a broader range of conditions. As natural products, GNC products are compatible with organic feed production.

Matrix values are routinely assigned to ingredients in an attempt to value NSP enzyme products.  Of course the stipulated matrix value is a major determinant of the perceived value of the enzyme, hence providers are encouraged to be aggressive in their stipulation.  There are several problems with this approach which nutritionists should bear in mind:

1. The enzyme response is not uniform among samples of an ingredient.  Wheat or barley energy availability may be affected by environment, variety, resting time after harvest, etc.  The enzyme response is greater in poorer quality grain samples than higher quality.  Moreover poor samples will be improved but generally not “all the way”. If the improvement due to enzyme response in a poor quality sample is applied to a high grade sample it will be overestimated. 

2. Enzymes violate the additivity assumption inherent in diet formulation.  i.e. One ingredient does not affect the digestibility of another.  (This is of course often not true, and historically controlled by specifying ingredient limits, for example.)  A major effect of viscous fiber is fat digestibility, and the removal of viscosity improves fat digestion, sometimes remarkably.  Calculation of energy availability of an ingredient also requires the additivity assumption (in a mixed diet), hence the improvement in energy from fat (in this example) is incorrectly attributed to the grain.

3. The enzyme response is not uniform across age.  Younger animals give a greater response than older animals.  If a matrix value is determined with young animals it will overestimate the enzyme improvement when applied to older animals. 

4. The matrix value “with added enzyme” also has the implicit assumption that the associated cost (enzyme level) is proportional to the level of ingredient in the diet when it is normally added as a constant.

5. In addition to adversely affecting nutrient balance, the stipulation of too high an energy value for an ingredient overvalues it.  The ingredient will be artificially retained in the formulation when real economics dictate it should have been reduced or deleted. 

So the question then is how to best handle the effects of NSP enzymes in the diet formulation system.  An alternative, manipulating the diet density, is theoretically more correct but in actual practice generally yields a similar diet.  The important point is that matrix values are approximations based on an imperfect system, and risk of errors increases with the aggressiveness with which they are applied.  While nutrition is a science, formulation is also an exercise in risk management.   The ingredient value/cost far outweighs the enzyme (per tonne feed) cost, and is the primary decision parameter.

 A newer version of matrix application applies an energy value to the enzyme itself, which has found widespread acceptance particularly where corn/soy diets predominate.  We still have the basic problem whereby the additivity assumption is violated.  The enzyme only has energy through its effects on other ingredients.  The assumption with the matrix value, is that thus applied all diets are assumed to give the same enzyme response.   GNC products exhibit activity on all plant-based ingredients, of course that is not the same as a biological response.  The biological response declines from corn/soy<wheat<barley, and different enzymes are involved (hence the preference for multi-enzyme systems).  The concern remains that declared matrix values would be the major determinant of cost/benefit, with strong pressures to claim high.  It will not be constant, and there is no easy way to determine experimentally.  It does offer the advantage of simplicity, which is important of course.