Age and adaptation to Ca and P deficiencies: 2. Impacts on amino acid digestibility and phytase efficacy in broilers.

A total of 1,152 straight-run hatchling Heritage 56M×fast feathering Cobb 500F broiler birds were used to determine Ca, age, and adaptation effects on apparent ileal digestibility of crude protein (AID of CP), amino acids (AID of AA) and phytase efficacy. Twelve treatments with 8 replicates, each were fed from 7 to 9 d (6 birds per replicate), 7 to 21 d (6 birds per replicate) and 19 to 21 d (3 birds per replicate) d of age. Diets were prepared with 3 Ca (0.65, 0.80, and 0.95%) and 2 non-phytate P, (0.20 and 0.40%) concentrations. A 6-phytase was added at 500 or 1,000 FTU/kg to the 0.20% nPP diet at each Ca concentration. The age and adaptation effects were determined by comparing the responses between birds fed from 7 to 9 and 19 to 21 d of age, 19 to 21, and 7 to 21 d of age, respectively. An age effect was observed regardless of Ca, nPP, or phytase concentration, with older birds (19 to 21 d) having greater apparent ileal digestibility (AID) of amino acids (AA) and CP than younger birds (7 to 9 d; P<0.05). Response to adaptation varied depending on Ca, nPP, and phytase concentrations. Constant lower AID of CP and AA was seen in adapted birds (7 to 21 d) compared to unadapted bird (19 to 21 d) when 0.20% nPP diets were fed at 0.95% Ca concentrations (P<0.05). At 0.40% nPP, there was no effect of adaptation on AID of CP and AA at any Ca concentration. Phytase efficacy was significantly lower in younger (7 to 9 d) compared to older birds (19 to 21 d; P<0.05), except at 0.65% Ca. Phytase inclusion increased AID of CP and AA regardless of Ca (P<0.05). In conclusion, the AID of CP and AA can be affected by diet, age, and adaptation.