Study On The Parameter Of Determining In Vitro Phosphorus Digestibility Of Swine Plant-origin Feedstuffs Using Bionic Digestion System

Four experiments were conducted to study the proper method for determining bionic phosphorusdigestibility, the suitable operating conditions and the necessity of3-step in vitro digestibilitytechniques.The first part was to study the effect of different molecular weight cutoff (MWCO) and source ofdialysis tubing (DT) on in vitro dry matter and phosphorus digestibility, which would provide areference for determining whether the in vitro phosphorus digestibility could be predicted using SDS.The single factor completely randomized design was adopted for the effect of different DT (Viskase forMWCO14000,3500and1000Da; Spectra/Por for3500and1000Da) on in vitro dry matter andphosphorus digestibility of corn, soybean meal and wheat bran. The results showed that with the narrowof molecular weight cutoff in Viskase DT, in vitro dry matter and phosphorus digestibility were reduced.Although in vitro dry matter or phosphorus digestibility of three feedstuffs using Spectra/Por DT withdifferent MWCO was not similar in the present study (P<0.05), the maximum difference between3500and1000Da of the three feedstuffs were only3.35%or1.67%. The phosphorus digestibility usingSpectra/Por DT with MWCO3500Da were higher than using Viskase DT with MWCO3500Da(P<0.05). In conclusion, Viskase DT with MWCO14000Da was more suitable for evaluation of invitro dry matter digestibility; the phosphorus digestibility using Viskase DT with MWCO3500Da wasclose to in vivo available P values for swine.The second part was to study the total phosphorus dialysance and inorganic phosphorus dialysanceof swine feedstuffs under different DT with the purpose of studying the proper method for determiningbionic phosphorus digestibility. Experiment1was to study whether existing dialysis tubing couldseparate inorganic phosphorus and organic phosphorus. The total phosphorus in undigested residue andinorganic phosphorus in dialysate were determined using DT with14000Da or3500Da. In theexperiment2, the in vitro phosphorus digestibility of swine common feedstuffs (corn, soybean meal,rice bran, canola meal, wheat bran) was determined by determining inorganic phosphorus in dialysateusing MWCO14000Da or3500Da DT. The results showed that there was organic phosphorus indialysate, which indicate that MWCO3500Da DT was unable to separate inorganic phosphorus andorganic phosphorus. So the in vitro phosphorus digestibility could not be estimated by determining thetotal phosphorus in undigested residue. In inorganic phosphorus determination experiment, thephosphorus digestibility determined using DT with MWCO14000Da was significantly higher than3500Da (P<0.05), and the coefficient of variation were all less than4%, which was lower than thosemeasured by other researchers(P<0.05). In conclusion, the existing dialysis tubing was unable toseparate inorganic phosphorus and organic phosphorus; the results of inorganic phosphorusdetermination using DT with MWCO14000Da was higher and accurate, so the method was moreappropriate for estimating phosphorus availability in swine feedstuffs.The third part aimed to obtain the suitable conditions of predicting in vitro phosphorus digestibility.Three volume of dialyzing solution levels(600,800,1000mL), three dialysate flow rate levels(283,425, 496mL/min)and two particle size levels(40,60mesh) were set up. The results showed that the volumeof dialyzing solution showed no significant influence on in vitro phosphorus digestibility of corn andwheat bran(P>0.05), but significant influence on that of soybean meal(P<0.05), the maximumdifference was only1.29%. The optimal volume was600~1000mL. There was not significantdifference in the phosphorus digestibility of swine feedstuffs with the increase of dialysate flowrate(P>0.05). No significant effect was found with smaller particle size on the phosphorus digestibility.The fourth part was designed to investigate the effect of large intestinal digestion on in vitrophosphorus digestibility. On the basis of two-Step in vitro digestion, the in vitro phosphorusdigestibility of two three-step in vitro digestibility techniques with either cellulase or Viscozyme wascompared to the blank control group. The results showed that the in vitro phosphorus digestibility ofcellulase group or Viscozyme group was not increased with control group. In conclusion, large intestinalin vitro digestion was not essential to in vitro phosphorus digestibility techniques.