Modeling improvements in digestible amino acids by a consensus bacterial 6-phytase variant in grower pigs

Data from 8 datasets generated from 5 independent experiments that determined the effects of a consensus bacterial 6-phytase variant (PhyG) on apparent ileal digestibility (AID) of amino acids (AA) in growing pigs (~21 to 45 kg body weight) were combined and modeled to test the hypothesis that the phytase results in significant improvements in ileal AA digestibility. The aim was to generate accurate and robust dose-related predictions of the digestible AA contributions of the phytase. The 5 experiments were conducted in Spain, Australia, USA, and Brazil and incorporated variation in diet composition (ingredient composition, phytate-phosphorus (PP) content, limestone solubility), diet form, animal breed and sex. A total of 325 datapoints (observations) were analyzed. First, the relationship between the percentage AID of AA and log-transformed phytase dose (range 0 to 4,000 phytase units (FTU)/kg, analyzed values) was modeled by log-linear regression across all datasets without adjustment for variation in the response to the negative control (NC) diet. The model predicted that the mean AID of total AA in the NC diets was 68.6% (range 43.3% [Cys] to 81.7% [Arg]). This was increased linearly by PhyG supplementation (P < 0.05), by 3.7 percentage units when dosed at 1,000 FTU/kg and by 4.5 percentage units at 4,000 FTU/kg. Second, the percentage unit change in the AID of AA at each phytase dose from baseline (NC without added phytase) was calculated separately for each dataset and the data then combined and modeled together by log-linear regression, against analyzed and log-transformed phytase dose. By this analysis, increases were evident for the AID of all individual (and total) AA. Increases (vs. baseline) at 1,000 and 2,000 FTU/kg were greatest for Trp (+ 6.1 and + 6.8 percentage units), Thr (+ 3.4 and + 3.8 percentage units after correction for synthetic Thr), Gly (+ 7.5 and + 8.3 percentage units) and Cys (+ 5.6 and + 6.2 percentage units). In conclusion, combined data from 5 separate experiments indicate that the bacterial phytase-6 variant will improve ileal digestibility of AA if included in diets fed to growing pigs. The data will allow diet-specific AA matrix recommendations to be made in commercial feed formulations containing PhyG.