There are many factors that impact enzyme feed additive effectiveness and results, one of the most important of which is enzyme stability, meaning the ability of the enzyme to maintain its activity level during both feed processing and animal digestion.  Xylamax Ribbon Model

Intrinsic stability characteristics are encoded in the molecular structure of an enzyme by its amino acid sequence which determines the structure and biophysical makeup of the enzyme. The enzyme structure must be both flexible and rigid; flexibility is necessary for efficient substrate breakdown and rigidity ensures structural stability of the enzyme.

Enzyme Stability During Feed Processing

Feed processing exposes enzymes to extremely high temperatures which can cause denaturation (loss of activity). Selecting an enzyme that is intrinsically thermostable (meaning that it naturally can withstand high temperatures) is one of the best ways to ensure that the enzyme is at full activity level when it is fed to the animal.  For more information about enzyme thermostability please refer to our blog “Why Does Enzyme Thermostability Matter?”

Enzyme Stability During Digestion

Once a chicken has ingested feed containing an enzyme feed additive, the enzyme must be able to breakdown the target substrate in a short amount of time, withstand a broad range of pH, and survive proteolysis by endogenous enzymes.

The digestive tract of a chicken is a tough environment that limits an enzyme’s ability to catalyze substrates as quickly as it can in laboratory conditions. Usually, the activity levels of an enzyme quoted by manufacturers are based on in vitro conditions, however, conditions are quite different in vivo.  The chicken digestive track is short, taking approximately 4.5 hours from ingestion to elimination. Therefore, an enzyme must exert its effect within a short window of time.

Enzymes must also be able to withstand harsh gut conditions, including drastic changes in pH. Enzymes vary in the optimum pH range under which they can effectively breakdown substrate material. Depending on the feeding program, feed retention time in the crop and gizzard may be very short. Hence, an enzyme with a wide pH range has the potential to work in numerous sections of the digestive tract. Comparatively, an enzyme with a narrow pH range has limited sections of the digestive tract where activity can occur. For example, some enzymes will have a pH optimum range between 4 and 6, indicating it will not function in the gizzard and proventriculus. Enzymes that have a pH range between 3 and 7 can function within more areas of the digestive tract. Thus, enzyme efficacy is improved with an enzyme which can operate within a broad pH range.




Another challenge to enzyme stability is the presence of proteolytic digestive enzymes in the digestive tract of animals, such as pepsin and trypsin.  These endogenous digestive enzymes have the ability to inactivate exogenous enzymes, or to limit their activity, thus reducing the enzyme efficacy. Stable enzymes can withstand proteolytic destruction by endogenous digestive enzymes.


To optimize the nutritional and gut health benefits of enzyme feed additives, it is necessary to carefully research the stability of each product being considered.  This can be done by running in vitro tests on the enzyme to test its ability to survive pH challenges, proteolytic enzymes, and its duration of activity. Once an enzyme with desirable characteristics is identified, testing must be done in vivo to confirm that these desirable characteristics persist thus optimizing the nutritional and gut health benefits desired.

Basheer Nusairat, Ph.D.

Animal Nutritionist, BRI




Bedford, M. R. and G. G. Partridge. 2010. Enzymes in farm animal nutrition. (Eds.) 2nd edition. CAB International, UK.

Mascarell, J., and M. Ryan. Technical aspects of enzyme utilization: Dry vs liquid enzymes, In:  Morand-Fehr, P. (ed.). Feed manufacturing in southern Europe: new challenges. Zaragoza: CIHEAM, 1997. p. 161-174 (Cahiers Options Mediterraneennes; no. 26).

Gaurav Shah. 2015. Three Reasons pH Impacts Enzyme Selection. BRI blog.

Markert, Y., J. Köditz, J. Mansfeld, U. Arnold, and R. Ulbrich-Hofmann. 2001. Increased proteolytic resistance of ribonuclease A by protein engineering. Protein Eng. 14 (10): 791-796.

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