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Today, there are many commercialenzyme products in the market,each with a seemingly ambiguoussystem of units and dosing rec-ommendations. The plethora ofmeasuring unit systems is be-cause the analytical method ofquantifying each enzyme activityis specific to this unique prod-uct. Each unit system is often de-veloped by the enzyme producerand the overriding purpose is to control and document enzyme activity in the enzyme productand finished feed or premix. Inaddition, as each enzyme productis derived from a distinct manu-facturing process (enzyme source,activity strength, and formulation)that determines its efficacy, differ-ent products can have differentrecommended dosages. Obvi-ously, this situation makes it extremely difficult to compare theefficacy of two enzyme products,and as such, enzyme units are nota suitable tool for this purpose.

In the case of phytases, the majormanufacturers have worked to-gether in standardizing the ana-lytical procedure for measuringthe activity in enzyme productsand feed samples. This was doneunder the auspices of FEFANA (EU association of feed additivesand premixture operators). Thestandard method was evaluatedin an inter-laboratory study in co-operation with the European Commission's Community Refer-ence Laboratory (CRL). Finally, themethod became an ISO (Interna-tional Organization for Standardi-zation) standard. In brief, onephytase unit (U) is the amount ofenzyme that releases 1 micromoleof inorganic phosphate perminute under specified laboratoryconditions: ie. from a 5 milli-molar solution of purified sodiumphytate at pH 5.5 and 37 °C.

Here it should be noted that activ-ity and concentration are two dif-ferent things. As such, unitsdescribing activity (such as thoseprovided for labeling purposes)have absolutely no value in com-paring two different products.Moreover, it is important to stressthat enzyme activity refers to the ability to perform a certain ac-tion under the specific assay con-ditions. And, as the assay condi-

tions are quite different from theconditions inside the animals, itis clear that the ability to performunder assay conditions is not theideal way to predict which of twodifferent phytase products will be most efficient in the animals.

So, what is the best way of comparing two phytase products?

First of all, products should becompared based on the cost ofapplication or saving potential (or ‘cost of treatment’) and not onthe cost per unit of phytase orcost per kg of product. The onlyvaluable method to compare en-zyme products is the performanceof the recommended dosage incarefully planned and conductedefficacy trials with the relevantanimal species. The real value ofa given enzyme product is there-fore the value obtained in the ani-mals (better performance orreduced feed costs) relative to theapplication cost. Naturally, otherquality parameters such as stabil-ity under storage and processing,mixability and safety should alsoto be taken into consideration.

In conclusion, two phytase prod-ucts can be compared only ontheir in-vivo efficacy, net feedcosts savings and other benefits.The units must be reserved for analytical purposes such as quality control and product documentation.

Phytase Unit Myth!

Maria Visiel VasquezRegional Category Manager

Feed EnzymesAsia Pacific, DSM

Maria-Visiel.Vasquez@dsm.com

Dr. Vibe GlitsoeScience Manager, Novozymes

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