Study On Determination Of Amino Acids Digestibility Of Feed Ingredients Based On Simulated Gastrointestinal Digestion Process For Growing Pigs

In this study,the amino acid(AA)digestibility of commonly used feed ingredients and diets of pigs were determined by in vivo assay and an in vitro simulated digestion system.The feasibility of in vitro simulated digestion method was verified by correlation and additivity analysis based on data from the 2 trials.The results of this study would provide references for rapid assessment of AA availability of feed ingredients for growing pigs.Experiment 1 was verified the accuracy of rapid determination of amino acid digestibility by simulated digestion method.Thirteen healthy castrated boars(initial BW =27.5±3.6 kg)with simple T-cannula at the terminal ileum were randomly allotted within a13 × 6 Youden square design.A total of 13 experimental diets were used for 6 periods of metabolic tests,with 6 replicates for each diet,and 1 pig per replicate.It includes 12 kinds of feed to be tested prepared from common feed raw materials for pigs and 1 kind of nitrogen-free feed.Each experimental period lasted for 7 d,including 5 d adaptation period and 2d ileal digesta collection period.The SID AA was determined,and the SDAA of feed ingredient was calculated.A single factor completely randomized design was used to determine the IVDAA content of 12 feed ingredients.Each feed sample was determined for5 replicates of 1 digestion tube per replicate with a computer-controlled simulated digestion system.The regression model of SDAA on IVDAA was established by regression analysis,and the accuracy and correlation of predicting SDAA of ingredients from IVDAA were explored.The result showed as follows: 1)In the digestibility of raw material amino acids determined by vivo assay,the SID of protein feedstuffs is generally higher than that of energy feedstuffs.The SID of total AA of wheat and expanded soybean were both higher than 87%,and the SID of total AA of rice DDGS was 75.53%,the least relative to other ingredients.The SID coefficient of variation of Lys in the protein feedstuffs were relatively less at about 5%,while the coefficient of variation of energy feedstuffs were between 10% to 20%,and the coefficient of variation of the total AA SID is basically below 5%.In terms of SDAA content,protein feedstuff is greater than energy feedstuff.The SDAA content of rice DDGS is the lowest among protein feedstuffs,which is close to that of wheat bran.2)The AA digestibility of protein feedstuffs measured by in vitro method was generally higher than that of energy feedstuff,which was similar to those of the biological method.The total AA digestibility of 43% soybean meal and expanded soybean was the highest and valued more than 88%.The total AA digestibility of brown rice was the lowest valued at 73.22%.3)The IVDAA from simulated digestion method had high correlation with the SDAA,the correlation coefficient of each amino acid is higher than 0.98 except Pro,and the absolute difference is about 0.05%.Linear regression equation of SDTAA on IVDTAA for 12 feed ingredients was: SDTAAin vivo=0.97× SDTAAIn vitro + 0.66(R~2=0.9980;RSD=0595;P<0.01).The regression models for several indispensable AA were as follows: Digestible Lys: SDLys=0.94 × IVDLys – 0.03(R~2=0.9950;RSD=0.068;P<0.01);Digestible Met: SDMet=0.94 × IVDMet(R~2=0.9878;RSD=0.029;P<0.01);Digestible Thr:(Thr): SDThr=0.92 × IVDThr(R~2=0.9982;RSD=0.024;P<0.01);Digestible Val: SDVal=0.93 × IVDVal +0.01(R~2=0.9952;RSD=0.047;P<0.01).Experiment 2 was conducted to explore the additivities of simulated digestion method in assessing the in vitro digestible AA(IVDAA)content of commonly used feed ingredients in growing pigs.Seven healthy castrated boars(initial BW = 26.5±3.1 kg)with simple T-cannula at the terminal ileum were randomly allotted within a 7 × 6 Youden square design.It includes 6 diets which were formulated with 4 or 5 of these individual ingredients for growing pigs and 1 kind of nitrogen-free feed.According to the SDAA of12 raw materials obtained in experiment 1 and its proportion in 6 diets,the calculated values of SDAA of 6 experimental diets were compared with the measured values in vivo and in vitro to verify the additivity of SDAA of 12 raw materials measured by two methods.The results showed as follows: In the additivity test of DAA in feed ingredients,the ratio of calculated and determined DAA by in vivo assay is between 95% and 115%;the ratio of calculated and determined DAA by simulated diegstion method is between 104% and124%,which indicted the additivity of the simulated digestion method is lower than that of the in vivo assay.In conclusion,the simulated digestion method can accurately assess the DAA content of commonly used feeds for pigs,but the additivity is not satisfied and needs to be further investigated and optimized.