The enzyme activity level provided by the manufacturer is often one of the first factors considered when selecting a new enzyme feed additive. While this is a seemingly logical first step in the evaluation process, activity level alone is not a robust indicator of product performance in the animal. What many end users do not realize is that enzyme activity is determined in a laboratory setting and is highly dependent on the context in which measurements were taken. A more in-depth understanding of the origin of activity levels is warranted to make an informed decision about their role in the evaluation and selection of enzyme feed additives.
How Enzyme Activity is Determined
- Activity Units
Enzyme feed additives are classically characterized by activity units. The standard enzyme unit is defined as the amount of enzyme that converts 1 µmol of substrate per minute (µmol/min). An enzyme activity is generally given in units/gram (U/g) or units/kilogram (U/kg), representing the units of enzyme activity present in a gram of an enzyme product. Some products are listed in alternative units to give the appearance of higher activity. To get an accurate picture, it is important to compare enzyme activity values using the same unit of measurement.
- Physical Conditions of the Assay System: Temperature and pH
Higher enzyme activity is dependent on the conditions in which the activity is measured. Temperature and pH are drivers of reactions and thus critical to the assessment of any activity level. The conditions are enzyme specific and generally reported with activity. Activity values are reported under the conditions where activity is found to be maximal. It’s not uncommon to see a 20 to 50 percent change in activity when the pH changes by one unit or the temperature changes by 5 degrees. Of far more importance, the tested conditions are not necessarily the conditions under which we expect the enzyme to perform in the bird (typically pH 6.0 – 7.0 and 41°C). Thus, care should be taken when comparing enzyme activity values obtained under laboratory conditions.
- Substrate Selection
When considering enzyme activity as a metric for product selection, one should also consider the substrate. Normally, an isolated and defined substrate is used to measure activity in the laboratory. In nature, the enzyme substrate exists within the complex structure of a feed grain. Feed grains consist of a mix of components, such as starch, non-starch polysaccharides (e.g., cellulose, arabinoxylan, beta-glucan and mannan) and proteins. The accessibility of each component by an enzyme is dependent on the structure of the feed-grain cell wall. Laboratory-derived enzyme activity levels cannot accurately reflect real production conditions.
How to Evaluate Enzyme Activity
Enzyme activity should not be the primary decision factor in enzyme selection. The environment in which an enzyme works inside the animal is quite complex. The harsh, dynamic conditions inside a bird’s digestive tract play a crucial role in enzyme efficacy. Enzyme additives must survive brutally acidic conditions from the crop (pH 4.0 – 6.0) through the gizzard (pH 2.0 – 5.0) for up to 90 minutes and then must be able to function as intended at a neutral pH. This environment is difficult to replicate in laboratory conditions.
Recognizing such difficulty, enzyme manufacturers and academic research institutions invest considerable resources in conducting trials using various diets under production conditions to accurately evaluate enzyme performance. The animal research trial summaries or articles they generate contain a wealth of information on the effective use of enzymes in actual production conditions. To ensure a complete understanding of an enzyme’s efficacy, it is highly recommended that you read multiple trials that were conducted under conditions and diets similar to those used by the producer.
However, the single most effective approach for evaluating an enzyme is to perform a trial in your own production facilities. The environment of a broiler house (light, temperature, etc.) has significant impact on enzyme performance within a bird. In addition, dietary formulation, feed quality and farm management methodologies vary widely across production facilities. The only true and consistent method that considers all possible variables impacting performance is evaluation of the product in the producer’s own facilities.
In summary, activity level is only one consideration when evaluating the potential of an enzyme feed additive. A wide array of factors (the animal, feed and environment) contribute to actual in vivo enzyme activity. An enzyme product’s real impact on animal performance can only be accurately measured by testing the product in the actual production conditions.
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Campbell, G.L. and M. R. Bedford. 1992. Enzyme applications for monogastric feeds: A review. Canadian Journal of Animal Science, 72(3): 449-466.
Robinson, P.K. 2015. Enzymes: principles and biotechnological applications. Essays in Biochemistry, 59:1-41.