Effects Of Phytase Level In A Low Phosphorus Diet On Growth Performance,Bone Development And Metabolism Of Calcium And Phosphorus In Weaned Piglets

Phytase plays an important role in saving the phosphorus resource and reducing the phosphorus excretion of animal feces.While the effect is influenced by many factors,such as the types of phytase,diet formulations,the level of dietary phosphorus and different growth stages of animal etc.The experiment was conducted to investigate the effects of a new phytase product supplementation in a low phosphorus diet on growth performance,bone development and metabolisms of calcium and phosphorus in weaned piglets in order to provide the experimental basis for the application of the new enzyme product.A total of 35healthy crossbred piglets（Duroc×Landrace×Large）with an initial average body weight of（7.62±0.44）kg were randomly allotted into 5 groups with 7 replicates per group and 1 pig per replicate.The treatments included basal diet,low phosphorus diet（pre-starter:5.1 g Ca/kg,2.0g STTD P/kg;starter:4.6 g Ca/kg,1.65g STTD P/kg）,and low phosphorus diet supplemented with 250,500,1000 FTU/kg phytase.The experimental period lasted for 21 d.On days 18～21,digestion experiment was carried out with endogenous markers and all the urine was collected.On the morning of day 22,all piglets after fasting for 12h were drawn blood via the jugular veins,and blood samples were collected,then all piglets were slaughtered.The results were as follows:（1）On days 1～14,low-P diets supplemented with 1000 FTU/kg phytase had a tendency to increase ADFI（P=0.07）;On days 15～21,low-P diets supplemented with 1000 FTU/kg phytase increased ADFI and ADG（P<0.05）;On days 1～21,low-P diets supplemented with1000 FTU/kg phytase increased ADFI（P=0.02）and ADG（P<0.01）.Compared with the control group,low-P diets supplemented with 250,500,1000 FTU/kg phytase increased digestibility of DM and OM;low-P diets supplemented with 1000 FTU/kg phytase increased CP digestibility,low-P diets supplemented with 500,1000 FTU/kg phytase increased the digestibility of GE,Ca and P.The effect of low-P diets supplemented with 1000 FTU/kg phytase was the best among all groups.（2）Referring to metabolic balance of phosphorus,low-P diets supplemented with 500,1000 FTU/kg phytase increased the absorption and the retention ratio of P（P<0.05）,and then decreased the fecal P excretion（P<0.05）.The effect of low-P diets with 1000 FTU/kg phytase supplementation showed the best.Compared with basal diet group,the fecal phosphorus excretion was reduced by 57.55%and decreased to 0.45 g/d,but there was no significant differences observed on the urine P excretion（P=0.95）.Given to the metabolic balance of calcium,low-P diet with 1000 FTU/kg phytase supplementation increased the absorption of Ca（P<0.05）,decreased the fecal excretion of Ca（P<0.05）.,Compared with basal diet group,the fecal Ca excretion was reduced by 67.74%and decreased to 0.30 g/d,but no significant differences of urine Ca excretion was detected（P=0.69）.（3）Low-P diets with 1000 FTU/kg phytase supplementation increased the length of the third metacarpal bone（P=0.01）.The breaking strength of the forth metacarpal bone,the fat-free dry weight,bone ash weight,and bone P and Ca of the third metacarpal bone were higher than those in control group.Compared with the low-P diets,low-P diets with 1000FTU/kg phytase supplementation increased the breaking strength of the forth metacarpal bone（P=0.04）,bone ash weight（P<0.05）,and bone P（P=0.03）and Ca（P=0.03）of the third metacarpal bone,respectively.（4）Low-P diets with 1000 FTU/kg phytase supplementation increased the content of P in serum on day 21（P<0.05）,and decreased the content of Ca in serum（P<0.05）.Low-P diets and low-P diets supplemented with 250,500,1000 FTU/kg phytase increased the content of AKP（P<0.05）in serum on day 21.Low-P diets and low-P diets supplemented with 250,500,1000 FTU/kg phytase increased the content of 1,25-（OH）₂D₃ in serum on day 21（P<0.01）,and there was no effects on the content of PTH in serum（P>0.05）.（5）There was no effects on morphology of the small intestine while phytases was added in low-P diets（P>0.05）.Low-P diets with 1000 FTU/kg phytase supplementation increased the activity of AKP in jejunum mucosa and the m RNA expression levels of SGLT-1 on ileum mucosal（P<0.05）.The conclusions of this study were as follows:（1）Low-P diets（corn-soybean meal based）supplemented with phytase significantly improved the performance of weaning piglets,increased the apparent nutrient digestibility and reduced the excretion of fecal phosphorus.（2）Low-p diets（corn-soybean meal based）with phytase supplementation increased the contents of Ca,P and the activity of AKP in serum,influenced the hormone level related to metabolisms of calcium and phosphorus,which resulted in the improvement of metabolic status of calcium and phosphorus and promoting bone development of weaned piglets.（3）Considering growth performance and bone development,the optimum adding dose of phytase in the corn-soybean meal based diets（1.65～2.0 g STTD P/kg）for feeding weaned piglets（weaned at 21 d）was 1000 FTU/kg.