Studies On Phosphorus Equivalency Of Phytase And Its Relations With Diet Structure In Growing Pigs

Since people are paying more attention on the serious pollution from eutrophication caused by blind and excessive use of inorganic nitrogen and phosphorus during livestock production,it becomes a pressing problem for sustainable development for livestock industry through raising nutrient utilization for nitrogen and phosphorus and reducing pollution of the environment.By considering the outstanding advantage of phytase on improving phosphorus utilization,and lacking of literature information on replacement capacity of phytase to dietary phytic phosphorus,hence,it is hard to guide feed production and livestock raising.This study is aimed to study the effects of application of phytase in different types of diets for growing pigs and the relations between the inorganic phosphorus exchange amount from phytase,diet structure and phytase efficiency,to acquire a mathematical model to describing the replacement capacity of phytase to inorganic phosphorus,and to verify the model with different diets structure for growing pigs,to provide an experimental base and scientific guidance for phytase use in enterprises engaged in animal raising and feed production.The main results of this study are as follows:1.The effects of phytase addition under the conditions of three typical dietsThe study was carried out to evaluate the effect of phytase on the phosphorus availability in different types of diets which corn,wheat or brown rice as the main energy source.The 3×2 factorial design method was adopted that six treatments including three basal diets above and the phytase(750FTU)was added in each diet respectively.In this experiment fifty-four growing pigs(DurocxLandracex Yorkshire)were allotted to six treatments randomly,each treatment had three replication pens with three pigs in each pen. The results showed that(1)phytase supplementation could significantly decrease feed gain ratio(P<0.05),but diet types have no significant effect on the feed gain ratio (P>0.05).(2)the excretion of fecal phosphorus were significantly reduced in the phytase added diets(P<0.05).To the reducing percentage of excretion of fecal phosphorus, 21.87%for wheat diet,15.37%for brown rice diet and 9.66%for corn diet respectively.(3) The level of serum P was significantly affected by phytase supplementation(P<0.05),but not by diet types(P>0.05). 2.Phosphorus equivalency of phytase for growing pigsThe objective of this study is to investigate the effects of exogenous adding inorganic P and phytase of feed on the utilization of phytic phosphrous and to determine the phosphorus equivalency of phytase.NaH₂PO₄·2H₂O was provided as an exogenous inorganic P.Took corn-soybean as low-P basal diet,4 gradual monosodium phosphate(MSP)as well as 3 gradual phytase were supplemented in basal diet to provide 0.4,0.8,1.2,1.6g/kg added P and 500,750,1000FTU/kg phytase,respectively,a total number of ninety-six growing pigs(DurocxLandrace xYorkshire)weighted about 22kg were allotted to 8 dietary treatment randomly,to establish the linear relationship between supplemental P and response indicator by determining the bone breaking strength and ash P content,evaluated equivalency in regression curve in terms of improvement of response indicator by phytase in diet.The results showed that:(1)animal growing performance increased significantly(P<0.05),ash P and serum concentration of inorganic P increased significantly(P<0.01)with increasing levels of MSP and phytase(750FTU/kg, 1000FTU/kg);(2)the level of inorganic P addition has a strong positive correlation with bone breaking strength and content of ash P y=10.79x+27.23(x-added P, y-metacarpal-metatarsal strength,R²=0.9221,P<0.05,n=15)or y=1.44x+6.86(x-added P,y-ash P,R²=0.9943,P0.01,n=15,).Based on corn-soybean meal diet,phosphorus equivalency of phytase displayed exponential-function relationship with different response indicators(adding quantity of phytase is between 0-1000 FTU/kg).The mathematical models are as follow:y=0.0527e^0.3056x(x-adding phytase,y-phosphorus equivalency of phytase,e=2.7183,R2=0.9854,P<0.01,n=15,bone ash P as a response indicator); y=0.0135e^0.4159x(x-adding phytase,y-phosphorus equivalency of phytase,e≈2.7183, R²=0.9155,P<0.05,n=15,bone breaking strength as a response indicator).3.The comparison of phosphorus equivalence of phytase in wheat based diet and in brown rice based dietSince north China is rich in wheat,south China is rich in rice,wheat diet and brown rice diet were chosen in this experiment to investigate the effects of phytase on phosphorus utilization and bone growth in growing pigs fed with different diets.Thirty-six castrated boars(Duroc×Landrace×Yorkshire)with an average initial weight of about 40kg were allotted to four treatments randomly;each treatment has three replicates of three pigs. The treatments were designed in a 2×2 factorial arrangement,and were as follows:(1) wheat diet without additional phytase,(2)wheat diet with additional phytase(947FTU/kg in totally,refer to the curve of phosphorus equivalency in experiment 2,which can substitute 0.7g inorganic phosphorus per kg diet,the same as follows),(3)brown rice diet without additional phytase,(4)brown rice deit with additional phytase.The results showed that(1)the bone breaking strength was not numerically different among the treatments (P>0.05),but addition of phytase can increase the bone breaking strength in the same diet(P>0.05);(2)The type of diet had no significant effect on the apparent digestibility of phosphorus(P>0.05),addition of phytase can increase the apparent digestibility of phosphorus in the same diet(P<0.05).The results of above three experiments suggested that adding phytase to diet has obvious effects on improvement of productivity of pigs,and of utilization of nutrients, particularly of phytic phosphorus.Phytase in diet has good synergistic action between endogenous resource and exogenous addition.The structure of diet has little effect.The selection of response indicators has great effect on phosphorus equivalency of phytase. Based on corn-soybean meal diet,phosphorus equivalency of phytase displayed exponential-function relationship with different response indicators(adding quantity of phytase is between 0-1000 FTU/kg).The established mathematical models are as follow:y =0.0527e^0.3056x(x-adding phytase,y-phosphorus equivalency of phytase,e≈2.7183,R2 =0.9854,P<0.01,n=15,bone ash P as a response indicator);y=0.0135e^0.4159x(x-adding phytase,y-phosphorus equivalency of phytase e≈2.7183,R²=0.9155,P<0.05,n=15, bone breaking strength as a response indicator).