Does supplemental dietary microbial phytase improve amino acid utilization? A perspective that it does not

ABSTRACT Environmental concerns regarding the excretion of large quantities of P in effluents from intensive animal production operations have led to the current routine use of microbial phytase. Following extensive investigations, microbial phytase supplementation of plant-based diets has been shown to consistently improve the utilization of plant phytin-bound P, and a plethora of data is available in the literature to support this. The release of P from plant phytin during the digestion process is theorized to release other nutrients that may be bound in the phytin complex. Furthermore, hydrolysis of phytin is hypothesized to attenuate the inhibitory effect of phytin on digestive enzymes and consequently to ameliorate the depression of nutrient absorption. Although a limited pool of data exists on small increases in apparent amino acid digestibility in swine and poultry literature, these increases have seldom translated into improved growth performance when the effect of enhanced phytin P utilization is factored out. Conversely, there are also data on a lack of response in amino acid utilization (both pre- and postabsorptive) to microbial phytase supplementation. Several factors might play important roles in amino acid utilization response to dietary microbial phytase supplementation. Identification of such factors and quantification of their effects on the magnitude of response to phytase would be important in ascribing a meaningful “amino acid response factor” (or amino acid equivalency value) to supplemental microbial phytase in plant-based diets and in moving the swine and poultry nutrition industry ahead.

Implications

The cost effectiveness of microbial phytase addition to swine and poultry diets would be considerably improved if it were established that the enzyme consistently improved protein and amino acid utilization. A lack of consistency in amino acid utilization response to phytase supplementation calls for caution in the use of any overly simplistic guidelines that ascribe an “amino acid response factor” to microbial phytase supplementation. Clearly, interactions among phytin, minerals, proteins, phytase, and protein-hydrolyzing enzymes and their effects on protein and amino acid utilization by the animal are a multifaceted subject affected by several factors that merit further research. The opportunity exists to identify these factors, quantify the magnitude of impact of the factors, measure actual response for specific feed ingredients and diets, and use the information generated for a more accurate diet formulation that matches animal amino acid needs with dietary supply.

Key Words: Amino Acids, Digestibility, Phytase, Phytin, Pigs, Poultry

© 2003, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2003. 81(E. Suppl. 2):E78-E85