Modeling improvements in ileal digestible amino acids by a novel consensus bacterial 6-phytase variant in broilers

Data from 13 datasets from 4 trials on the effect of a novel consensus bacterial 6-phytase variant (PhyG) on the apparent ileal digestibility (AID) of amino acids (AA) in broilers were used to model AID AA responses. The datasets were obtained from 3 trial locations (New Zealand, Australia and United States) and collectively incorporated variations in diet composition (feedstuff composition, phytate-P (PP) level, limestone solubility), feed form (mash or pellet), bird genetics (strain), and age at sampling (11–35 d of age). In total, 384 observations were analyzed. First, the relationships between AID of AA (as coefficients) and increasing phytase dose level from 0 to 4,000 FTU/kg were evaluated across all datasets using exponential curve fitting. Second, the percentage unit change in AID of AA at each phytase dose level from baseline (basal diet [BD] without phytase) was calculated separately for each dataset and the data then modeled together using exponential curve fitting. The model-predicted mean coefficient of AID of total AA in basal diets was 0.76 (range 0.56 [Cys] to 0.83 [Glu]), which was increased by PhyG to 0.80 and 0.81 at 2,000 and 4,000 FTU/kg, respectively. Exponential increases in the percentage unit improvement in AID of 18 individual and of total AA with increasing phytase dose level were evident (P < 0.05). Improvements (vs. BD) at 2,000 FTU/kg and 4,000 FTU/kg, respectively, were greatest for Cys (+9.2 and +11.0% units), Met (after deduction of synthetic Met, +8.4 and +9.0% units), and Thr (after deduction of synthetic Thr, +6.2 and +7.3% units). The data demonstrated consistent improvements in the AID of AA by the phytase. The modeling results generated from data gathered from birds sampled at different ages and from different dietary settings with correction of synthetic AA for Lys, Met, Thr, and Trp, enabled a more accurate prediction of the digestible AA contribution from the diet by this novel phytase. This will allow diet-specific AA matrix recommendations to be made in commercial feed formulations

Effects of phytase supplementation of phosphorus-adequate, lysine-deficient, wheat-based diets on growth performance of weaner pigs

The effects of microbial phytase supplementation of phosphorus-adequate, wheat-based diets with available lysine : energy density ratios ranging from 0.75 to 0.90 g available lysine/MJ DE on growth performance of weaner pigs were investigated in 3 studies. In the first study, increasing levels of dietary phytate depressed growth rates (P&lt;0.08) and efficiency of feed conversion (P&lt;0.01) and phytase supplementation enhanced growth rates (P&lt;0.05) and tended to improve feed efficiency (P&lt;0.15). There were no significant interactions between dietary phytate and phytase inclusion to support the hypothesis that dietary substrate levels of phytate govern responses to phytase. However, in this and other studies, percentage increases in efficiency of feed conversion generated by phytase were positively correlated to dietary phytate concentrations to a significant extent (P&lt;0.005), so it is possible that dietary substrate levels are of importance to the magnitude of responses following phytase supplementation. Diets with 3 levels of protein, expressed as 0.80, 0.85, and 0.90 g available lysine/MJ DE, were offered to pigs without and with phytase in the second study. Protein/amino acid levels or lysine : energy density ratios did not influence growth performance, which was not expected. However, phytase tended to increase growth rates (P&lt;0.08) and improved feed efficiency (P&lt;0.01). Although it is believed that phytase may have a positive influence on protein utilisation, this was not demonstrated in this experiment. In the third study, the simultaneous inclusion of phytase and xylanase feed enzymes in wheat-based weaner diets did not increase growth performance responses in comparison with phytase alone. Individually, phytase improved feed efficiency (P&lt;0.05) and numerically increased growth rates (P&lt;0.25). Although responses in growth performance of weaner pigs following phytase supplementation lacked consistency, they were generally positive and indicative of anti-nutritive properties of phytate that are unrelated to P availability. That these positive responses were observed in diets with suboptimal available lysine : energy density ratios is consistent with the possibility that phytate has a negative influence on protein utilisation, which is ameliorated by phytase. However, these antinutritive effects and their underlying mechanisms need to be better defined if full advantage of the potential protein-sparing effects of microbial phytase is to be taken

Total and phytate-phosphorus contents and phytase activity of Australian-sourced feed ingredients for pigs and poultry

A total of 160 samples of 20 Australian-sourced feed ingredients of plant origin for pigs and poultry was analysed for total phosphorus and phytate-phosphorus contents and endogenous phytase activity. The majority of total P was present as phytate-phosphorus, and these concentrations were significantly correlated in 9 feed ingredients. The endogenous phytase activity in tested feed ingredients was negligible other than for wheat, its by-products and barley. Phytate-phosphorus was determined by a standard 'ferric chloride precipitation' method, which was satisfactory for individual feed ingredients, with the exception of lupins and faba beans. It appears that phytate is more difficult to extract from these two feedstuffs, possibly because of the affinity of phytate for protein. Ferric chloride precipitation methods are not suitable for phytate-phosphorus determinations of complete feed samples containing other sources of phosphorus, which is a distinct limitation. A lesser limitation is that these methods cannot distinguish between the various esters of myo-inositol phosphate present. Given the variation of phytate contents within ingredients, particularly wheat, the desirability of determining dietary substrate levels is emphasised to take full advantage of including exogenous phytases in pig and poultry diets to reduce phosphorus excretion and abate phosphorus pollution