| The objective of this study was to estimate the influence of different inorganic phosphorus(P)levels of diets with phytase supplementation on Bones Calcium and Phosphorus metabolism and intestinal NaPi-IIb gene expression in weaned piglets.A total of two hundred and twenty-four healthy post-weanling pigs(Duroc×Landrace×Largewhite) with an average of(9.12±0.29)kg were randomly divided into 7 treatments with 4 replicates in each treatment, and 8 piglets per replicate. The control group was fed a basal diet, groups 2 to 6 were fed diets with the same calcium(Ca)level(7.0 g/kg) and phytase supplemented(750 FTU/kg), and inorganic P addition was 100% 、 75%, 50%,25%,0%(Ca to total phosphorus(TP)ratio was 1.17~1.79:1)of the control group respectively;Group 7 did not supplemented with phytase and inorganic P. The weanling pigs were fed the experimental diets for 35 d.The results showed that in the group without P, supplementation of phytase significantly improved the phosphorus content of tibia and ribs(P<0.01), and significantiy reduced the serum CT、OPN(P<0.05). In normal P level groups, supplementation of phytase significantly improved the serum BAP(P<0.05);, and significantiy reduced the serum CTX-Ⅰ、OPN、TRACP-5b(P<0.01).With phytase supplemented, the reduction of dietary P level resulted in the linear(P<0.01) and quadratic(P<0.01) reduction in bone fresh weight, defatted weight, bone calcium, phosphorus and ash contention; and a linear(P<0.01) or quadratic(P<0.01) increase in serum CT、CTX-Ⅰ、OPN、TRACP-5b、l,25-(OH)2D3;and linear(P<0.01) and quadratic(P<0.01) reduction in serum FGF23、BAP、BGP、OPG。These results indicated that low phosphorus diets will weaken the effect of bone formation and promote bone formation. The serum BAP、OPG、BGP levels were positively correlated with serum P、FGF23 level and tibia calcium,phosphorus,ash contention, and negatively correlated with serum CT 、l,25-(OH)2D3 levels; The serum CTX-Ⅰ、OPN、TRACP5b levels were positively correlated with CT、l,25-(OH)2D3 levels, and negatively correlated with serum P、FGF23 levels and tibia calcium,phosphorus,ash contention;The serum BAP、OPG、BGP levels were positively correlated with CTX-Ⅰ、OPN、TRACP5b levels. These results indicated that bone metabolic biochemical markers can reflect the situation of calcium and phosphorus metabolism.In normal P level groups and the groups without P supplementation of phytase significantly reduced the expression of NaPi-IIb mRNA in small intestine of weaned piglets(P<0.01). With phytase supplemented, the reduction of dietary P level significantly improved the expression of NaPi-IIb mRNA in small intestine(P<0.01) and CaBP-D9 k mRNA in duodenal and renal(P<0.05)of Weaned piglets; and there have no significantly differents in the expression of jejunum and ileum of Ca BP-D9 k mRNA. Both inorganic phosphorus and phytase have no significant effect on the expression levels of intestinal SGLT-1 mRNA of weaned piglets(P>0.05). Immunohistochemistry showed that,NaPi-IIb protein was mainly distributed in cytoplasm of intestinal villus absorptive cells along the striated border, and also exist in some laminae propria cells. Dietary inorganic phosphorus levels decreased from 100% to 50% and 0%, Intestinal villus absorptive cells cytoplasm gradually become darker. This suggests that NaPi-IIb protein concentration in the cell increases with the decrease of dietary phosphorus level. Dietary phosphorus levels can stimulate the intestinal active absorption of phosphorus and improve its absorption efficiency.In conclusion, Phytase can improve bone performance of weaned piglets, and the effect is more obvious under low phosphorus conditions. Adding phytase diet, reduce the amount of inorganic phosphorus can reduce bone calcium, phosphorus and ash content in weaned piglets and promotes the expression of NaPi-IIb protein and its mRNA in small intestine. Biochemical markers of bone metabolism can accurately reflect the status of bone metabolism, and are more sensitive than conventional index. Integrated indicators, in weanling pigs diets, phytase can replace 25%(4.02 g/kg)of the dicalcium phosphate added amount. |
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