131 The effect of increasing phytase dose to 1000 FTU/kg on phosphorous and calcium digestibility in pigs fed diets without inorganic P

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Abstract An experiment was conducted to compare two sources of phytase, Buttiauxella phytase expressed in T. reesei (Phytase B) and a hybrid phytase expressed in A. niger (Phytase H), on the apparent total tract digestibility (ATTD) of phosphorous (P) and calcium (Ca) in pigs fed diets without inorganic P. Eighty barrows (12.8 ± 1.04 kg) were placed in metabolism crates and fed 8 diets (10 pigs/diet). A positive control diet (PC) based on corn, wheat, canola meal, and soybean meal was formulated to contain 0.29% standardized total tract digestible (STTD) P and 0.60% Ca. A negative control (NC) was formulated without inorganic P, and this diet contained 0.48% Ca and 0.19% STTD P. Six additional diets were formulated by adding 250, 500, or 1000 units of each phytase (FTU)/kg to NC. After 5 d of adaptation, feces were collected from the feed fed during the following 4 days. Data were analyzed using contrast statements to compare source of phytase and determine the linear and quadratic effects within each source of phytase. With increasing dosage, fecal excretion of P decreased with phytase B (quadratic, P < 0.05) and tended to decrease with phytase H (P < 0.10), but fecal P was greater (P < 0.05) for phytase H than phytase B. The ATTD of P increased quadratically with increasing dose of either phytase B or phytase H (P < 0.05). Across dose levels, phytase B had greater (P < 0.05) ATTD of P and Ca (77.3 and 83.5%) than phytase H (71.0 and 79.3), indicating that phytase B increases the ATTD of P and Ca to a greater extent than phytase H. In conclusion, both phytase B and phytase H, to a different extent, reduced fecal P excretion and increased ATTD of Ca and P in a dose dependent manner.