A systematic view on the effect of phytase on ileal amino acid digestibility in broilers

A total of 24 independent peer-reviewed papers on the effect of phytase on the coefficient of apparent ileal amino acid digestibility in broilers were used in a meta-analysis to explore response patterns. Transcription of the digestibility responses from all papers resulted in a database with 745 observations from diets based on various cereals (mainly corn), protein meals (mainly soybean meal) and by-products (ricebran, wheatbran etc). Most of the papers were published between 1996 and 2006 though several were published more recently (up to and including 2015) and included doses of phytase from 500 to 2000 FYT/kg. The mean coefficient of apparent ileal amino acid digestibility in the control was 0.80 and this was increased by the inclusion of phytase to 0.84 (+4.1%). The coefficients of apparent Lys, Met, Cys and Thr digestibility were increased by 3.4%, 1.3%, 7.2% and 6.0% respectively. A significant negative correlation was observed between the digestibility of the amino acids in the control diet and the magnitude of response to exogenous phytase, where phytase effect (on a relative and absolute basis) was lower in diets with a higher inherent amino acid digestibility. Elevation of phytase dose from 500 to 1000 FYT/kg resulted in an increase in amino acid digestibility coefficients from around 2% to around 4% but further increases to 2000 FYT/kg had no further positive effect. A significant relationship was noted between the proportion of dietary phytate destroyed by exogenous phytase and the effect of phytase on ileal amino acid digestibility coefficients where phytase effects ranged from 2 to 3% to 9–10% as phytate destruction increased from <10% to around 50%. Finally, there was a significant negative effect of diet phytate concentration per se on ileal amino acid digestibility in the control diets. These data confirm the efficacy of phytase to promote ileal amino acid digestibility in broilers with a mean response of around 4%. Furthermore, the pattern of response across all amino acids is supportive of previous observations that much of the beneficial effect stems from a reduction in the loss of endogenous protein from the intestine. The antinutritional effects of phytic acid are confirmed in the present analysis and the removal of this by the activity of phytase leads directly to an increase in amino acid digestibility. It can be concluded that matrix values for phytases for amino acids in the region of 2–6% (depending on the amino acid) are justified and that these values should be directly tied to P release (and axiomatically to phytate destruction). Phytases with equivalent P release recommendations for a given inclusion concentration should carry similar amino acid matrix values and the data presented herein offer clear evidence for industry benchmarking of phytase value.