Effects On The Growth Performance, Nutrient Digestibility And Bone In Nursery Pigs Fed Diets Added Phytase With Different Levels Of Inorganic Phosphorus

The trial was to study the effect of phytase supplementation in nursery pigs fed diets with different levels of inorganic phosphorus(P) on the growth performance, serum biochemical parameters, apparent digestibility of nutrients and bone quality. A total of 224 40±2-day-old nursery pigs were divided into seven treatment(TRT) with four replicates per group and there were 8 piglets in each replicate. Pigs in the TRT Ⅰ(control group) were fed a basal diet prepared according to the NRC(1998), adding calcium hydrogen phosphate to meet phosphorus requirement. TRT Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ, added 750 FTU/kg of phytase, were respectively supplemented with 100%,75%, 50%, 25%, 0% of dicalcium phosphate in control group. No dicalcium phosphate and phytase were added in TRT Ⅶ(negative control group).The results showed as follows:(1) The average daily feed intake(ADFI), average daily gain(ADG) and the feed conversion ratio(F/G) of the groups of 100%,75%, 50% dicalcium phosphate added phytase were not significantly different with the control group(P>0.05).(2) Serum Ca, Cu, Zn and Mn concentrations were not significantly different among treatments(P>0.05). The concentrations of serum P and serum Fe in the group of 100% dicalcium phosphate added phytase were the highest and were significantly higher than the control group(P<0.05), while the activities of serum alkaline phosphatase(ALP) and the apparent digestibility of Ca, P, crude protein(CP) and dry matter(DM) were not significantly different with the control group(P>0.05). The apparent digestibility of Ca and P of the group without dicalcium phosphate added phytase were the highest and were significantly higher than the negative control group(P<0.05). With the reduction of dietary inorganic P levels, the serum P, Fe concentrations of the phytase groups had reduced linearly and quadraticly effects(P<0.01), while the serum ALP activities and the apparent digestibility of Ca, P, CP and DM had increased effects of linear and quadratic(P<0.01). It can be seen that the phytase addition in the diet reducing the amount of inorganic P improved the digestibility of nutrients, and effect of phytase was more significant in lower inorganic P level.(3) The feces P contents of the phytase groups decreased by 0.52%、3.14%、9.42%、20.42% and 24.61% with the reduction of dietary inorganic P levels, illustrative the phytase addition in the diet reducing the amount of inorganic P can decline the P contents of faeces(4) Tibial fresh weight were not significantly different among treatments(P>0.05). The fat-free rate and Ca, P, ash concents of tibial were not significantly different with the control group(P>0.05), while the P concents of tibial of the group without dicalcium phosphate added phytase were significantly higher than the negative control group(P<0.05). With the reduction of dietary inorganic P levels, the concents of Ca, P and ash in tibial of the phytase groups had reduced linearly and quadraticly effects(P<0.05), and the fat-free rate of tibial had increased effects of linear and quadratic(P<0.01). Reduce 25% of inorganic P in the diets has little effect on the concents of P and ash in tibial(P>0.05).(5) The m RNA expression levels of Na Pi-Ⅱa in the kidneys of the groups of 100% and 75% dicalcium phosphate added phytase were not significantly different with the control group(P>0.05). The m RNA expression levels of Na Pi-Ⅱa of the negative control group were the highest, but were not significantly different with the group without dicalcium phosphate(P>0.05). With the reduction of dietary inorganic P levels, the m RNA expression levels of Na Pi-Ⅱa of the phytase groups were decreased.In summary, under the experimental conditions, the diet which were added by the phytase and reduced the amount of inorganic P improved the digestibility of nutrients, production performance of nursery pigs and reduced the P content in feces, besides there is no significant effect on the concents of serum Ca, Cu, Zn and Mn. A Adding phytase in lower P level diets had not only improved the apparent digestibility of Ca and P but also promoted the deposition of P in bones well. It is suggested that adding 750 FTU / kg phytase in the diets of nursery pigs might reduce 25%-50% of dicalcium phosphate supplementation.