Phytase Supplementation, Irrespective of Dietary Phytate Levels, Improves Digestibility of Amino Acids in Finisher Broiler Chickens

All grains, vegetable-based protein meals and their by-products used in poultry diets contain some levels of phytate phosphorous (PP). Depending on the ingredient type and source, a typical broiler chicken diet would contain between 2.2 to over 3.5 g/kg dietary PP. Research has shown that phytate anti-nutritional effects can reduce the digestibility of amino acids (AA) and minerals. Previously the effect of phytase on AA digestibility was reported in broilers at 21 days of age (Toghyani et al., 2021). This study reports the AA digestibility in the finisher phase.

The current study evaluated the effect of incremental doses (0, 500, 1000, 2000 and 4000 FTU/kg) of a novel consensus bacterial 6-phytase variant (PhyG) on AA digestibility in broilers at 35 days of age. The basal diets were formulated to contain either 2.45 g/kg, 2.95 g/kg or 3.45 g/kg phytate phosphorus (PP). However, the analyzed PP levels were greater than formulated, being 2.85, 3.43 and 3.87g/kg, in low, medium and high PP diets, respectively. A total of 1800 (Ross 308) day-old male chicks were randomly allocated to 90 battery cages with 6 replicate cages of 20 birds per treatment, creating a 3 × 5 factorial arrangement. Birds were offered diets deficient in available P (AvP) and Ca based on the expected contribution of 1000 FTU/kg PhyG, 2.77 g/kg AvP and 7.6 g/kg Ca in starter (0-10d), 2.25 g/kg AvP and 6.4 g/kg Ca in grower (10-21d), and 1.73 g/kg AvP and 5.5 g/kg Ca in finisher (21-25d). All the diets were formulated to be iso-nitrogenous and iso-caloric and balanced for all the essential AA based on Ross 308 broiler recommendations. On day 35, four birds per cage were euthanized to collect distal ileum content. Samples were pooled per replicate cage and analyzed for AA to calculate ileal digestibility. Increasing dietary PP decreased (P < 0.001) the average ileal digestibility of all the AA tested, by 1.5 and 2.2 % in medium and high PP groups, respectively, compared to low PP. There was no interaction of phytase and PP levels for the digestibility of any of the AA. Phytase inclusion, as the main effect, improved (P < 0.001) the ileal digestibility of all essential and non-essential AA tested, regardless of PP levels. Fitting exponential models predicted an average digestibility improvement, above negative control diets with no phytase, of 0.5 to 3.1 % at 500 FTU/kg, up to an average of 2.7 to 8.4 % at 4000 FTU/kg. Amongst the essential AA and at each level of phytase inclusion, methionine had the lowest (0.5 to 2.8 %) and threonine had the highest (2.7 to 8.4 %) predicted digestibility improvement. For the nonessential AA, the lowest and the highest digestibility improvement were predicted for glutamine (0.98 to 3.0 %) and tyrosine (3.1 to 8.1 %), respectively. The data obtained in this study indicate that dietary phytate, even in finisher broiler chicks, decreases AA digestibility, and exogenous phytase, at each level of inclusion (from 500 to 4000 FTU/kg) improves AA digestibility, irrespective of dietary PP levels.

ACKOWLEDGEMENTS: The authors would like to thank Danisco Animal Nutrition & Health (IFF) for financially supporting this research trial.