| Four experiments were conducted to explore factors that affect phytate phosphorus, amino acids (AA) and minerals release generated by phytase in pigs. In Exp.1, ten ileal T-cannulated pigs were used in a doubly replicated5×4incomplete Latin square design (5diets with4periods). The5diets were P deficient basal diets (0.38%total P) with0,500,1,000, or20,000FTU/kg phytase and a positive diet with adequate P (0.52%total P). There were linear increases (P<0.05) in the apparent ileal digestibility (AID) of dry matter (DM), energy, crude protein (CP), calcium (Ca), total P, phytate P and several AA. Phytase supplementation linearly increased (P<0.05) the apparent total tract digestibility (ATTD) and retention of Ca, total P, Mg, Mn and Zn, as well as ATTD of Na and K. High dose phytase supplementation continuously increased (P<0.05) the AID of Ca, total P and phytate P, and reduced (P <0.05) ileal phytate P concentration compared with normal dose phytase inclusion (500or1,000FTU/kg). High dose phytase supplementation, but not normal dose phytase (500or1,000FTU/kg), improved (P<0.05) the AID of several AA, DM, energy and CP, as well as the ATTD and retention (%) of Mn and Zn and digestibility of Na and K. Hindgut fermentation of crude fiber and neutral detergent fiber (NDF)(P<0.05) were suppressed by high dose phytase supplementation in P deficient diets. In Exp.2,120crossbred piglets were randomly allocated to1of5treatments which consisted of four low P diets (0.46%total P) supplemented with0,500,1,000, or20,000FTU/kg phytase as well as a positive control diet (0.62%total P). Each treatment had6replicated pens with4pigs per pen. Pigs were fed the experimental diets for28d. Phytase supplementation linearly improved (P<0.05) average daily gain (ADG), feed conversion ratio (FCR), and the ATTD of dry matter, gross energy, crude protein, Ca and P in weaned pigs. Super high dosing with phytase (20,000FTU/kg) further increased (P<0.05) ADG compared with500FTU/kg phytase inclusion, as well as the ATTD of Ca and P. Metacarpal bone characteristics and several trace mineral concentration in bone, plasma or organ tissues were linearly (P <0.05) improved with increasing dose of phytase. Super high dose phytase (20,000FTU/kg) supplementation improved (P<0.05) Mn and Zn concentration in the metacarpal bone compared with normal dose of phytase supplementation (500or1,000FTU/kg). In Exp.3,16ileal T-cannulated pigs were used in a doubly replicated8×3incomplete Latin square design (8diets with3periods). The8experimental diets followed2×2×2factorial design including0or1,000FTU/kg phytase,0or300mg/kg non-starch polysaccharide (NSP) enzymes, based diet with a high or low level of NSP (7.56%vs.11.60%NSP) and all combinations. Pigs fed high NSP based diets had lower (P<0.05) AID of phytate P and all AA, as well as lower AID or ATTD of proximate nutrients and NSP. Hindgut fermentation of NDF, insoluble and total NSP were depressed (P<0.05) by high NSP based diets. Phytase supplementation improved (P<0.05) AID of phytate P, Ca, total P and several AA, as well as the ATTD of ash, Ca and total P. There were significant interactions between NSP level and NSP enzymes supplementation for AID of phytate P, several AA, NSP and its monosaccharides, as well as other proximate nutrients. In addition, NSP enzymes supplementation improved the AID of all the nutrients above in the high NSP based diet, but not in the low NSP based diet. In Exp.4,192piglets (weaned at d28) were randomly allotted to one of8experimental diets for21days. Diets included0or1,000FTU/kg phytase, supplemental ZnO [control (CONT),500mg/kg Zn as encapsulated ZnO (CZ500),500or2,250mg/kg Zn as ZnO (Z500or Z2250)] and all combinations of phytase and ZnO. The basal diet was a P-deficient diet.The results demonstrated that phytase supplementation and CZ500improved (P<0.01) ADG and FCR in weaned pigs fed the P-deficient basal diets. Phytase supplementation resulted in a decrease (P<0.01) in phytate P concentration in the stomach digesta and increases (P<0.01) in bone breaking strength, ash, Ca and P weight of the third metacarpal bone, as well as serum P concentrations and ATTD of P. However, all the beneficial effects of phytase supplementation shown above were reduced (P<0.05) by a super dose of ZnO supplementation (Z2250), but not by encapsulated ZnO supplementation (CZ500). About76.6%or67.4%of ZnO (Z500or Z2250) was dissolved in the stomach, accompanied with an increase (P<0.01) in the stomach pH, while a smaller (P<0.01) percentage of encapsulated ZnO (6.6%vs.76.6%or67.4%) was dissolved in the stomach without changing the pH. CZ500and Z2250reduced (P<0.05) serum major acute-phase protein concentrations and improved bone and serum Zn levels, as well as the ATTD of DM and energy. However, in the same dietary Zn level (500mg/kg), pigs fed CZ500showed lower (P<0.01) serum pig major acute phase protein concentration and higher (P<0.01) ATTD of DM, energy and CP compared with pigs fed Z500. In conclusion, high dose phytase continuously hydrolyzes phytate P and improves utilization of AA and minerals. Synergic effects between phytase and NSP enzymes were observed in diets with a high NSP and phytate content. High levels of ZnO, but not encapsulated ZnO, impaired phytase efficacy in weaned pigs fed a P deficient diet. |
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