Phytase studies in pigs and poultry: effect on protein digestion and energy utilization

Phytase is applied for improving digestibility of phosphorus in pig and poultry diets. Indepen-dently, phytase also improves animal performance. The mechanisms to explain this effect were investigated and quantified. Protein can be complexed with phytate, especially under the acid conditions that occurs in the stomach of animals. Dietary phytase supplementation pre-vents formation of such complexes or, if such complexes are formed, helps to release protein faster and to a larger extent from phytate. Consequently, protein digestibility may increase. This effect was confirmed in a meta-analysis of digestibility experiments, both in poultry and pigs. The higher protein digestibility explains, only in part, the improved performance. In poultry, the apparent metabolizable energy level increased with dietary phytase, mainly as the result of higher protein and fat digestion. Because in literature no effect of phytase on energy digestibility in pigs was shown, post-absorptive energy utilization was investigated. Using indirect calorimetry, no clear effect of phytase could be shown on energy partitioning. Phytase improved, however, energy utilization during the first two weeks post-weaning of ad libitum fed piglets. This may indicate that adaptation of piglets is somewhat facilitated by phytase. In an experiment with restrictedly-fed piglets, three weeks post-weaning, energy digestibility increased with phytase, but not energy metabolizability. A number of observations indicated, however, that energy metabolism of the piglets was affected. Processes that increase or de-crease heat production balance each other out. Phytase increased digestibility of minerals considerably, including the monovalent cations sodium and potassium. Mineral absorption and excretion are, in part, active processes, increasing heat production. Using a mathematical model, this effect was estimated at about 1% of energy requirements for maintenance. A lower energy requirement may result from a reduced produc-tion of endogenous protein. In growing pigs, dietary phytase supplementation decreased gastric mucin production. Possibly, the for-mation of inositol mono-, di- or tri-phosphates may act positively on the growth of animals, but this remains to be confirmed. In conclusion, phytase improved digestibility of amino acids, both in poultry and pigs. It also improved energy metabolizability in poultry. Energy utilization in pigs is probably affected, but the mechanism needs further clarification and quantification.