Research On Estimating Digestible Energy And Metabolizable Energy Of Pig Diets And Ingredients Based On Chemical Analysis And Biomimetic Digestion Method

This study mainly compares the accuracy of chemical analysis estimation method and the bionic digestion method on digestive energy(DE)and metabolizable energy(ME)estimate in pig diets and feed ingredients.Experiment one compares the variation and additivity of the gross energy(GE)measured in different laboratories,to provide a reference for the accuracy of the GE analysis of feeds.The first test was to investigated the effects of the feed sample weight on the GE value analysis by the oxygen bomb calorimeter.Sample weight at 0.2,0.4,0.6,0.8 and 1.0 g was adopted for each of 6 feed ingredients and 10 diets.Each treatment contained 4 replicates.On this basis,we investigate the variation and additivity of diet GE between laboratories.The results showed that measured GE of 6 feed ingredients and 10 diets increased linearly and quadratically with the increment of sample weights(P<0.05).The measured GE values at sample weight of 0.2 g were lower than the GE values measured at sample weight of 0.4 to1.0 g(P<0.05).Relatively little difference was observed in GE measured at sample weights of 0.6 to1.0 g.In the comparison among 6 laboratories,the measured GE in laboratory 2 was lower,whereas the measured GE in laboratory 5 was higher than other laboratories.The variation of GE measured in laboratory 5 and 6 was relatively greater.In total,the coefficient of variation for repeatability,inter-laboratory and reproducibility of GE didn’t exceed 0.64%.No significant differences between the calculated and measured GE of 10 diets were observed in each of laboratory 1,3,5 and 6.Whereas,significant differences between the calculated and measured GE of 10 diets were observed in each of laboratory 2 and 4(P<0.05).The linear regression model of measured on calculated GE in 6 laboratories expect lab5overlapped with Y=X.This indicates that the loading volumes of sample for GE measurement using the oxygen bomb calorimeter should be more than 0.6 g.The GE value of feed measured in 6 laboratories show good consistency,and low coefficient of variation is observed in GE measured among laboratories.In the second experiment,the DE and ME of growing pigs on 20 feed ingredients and 10diets prepared with the above ingredients were measured to investigate the additivity of biological methods.The experiment selected 30 38.9±4.7 kg BW and 30 35.8±4.7 kg BW healthy castrated boars in two batches.Each batch of pigs was divided into 2 groups according to body weight.Two 15×3 incomplete Latin square designs were adopted.Each batch of pigs was tested with 15 diets.A total of 3 phases of metabolism test were carried out,with 6 replicates for each diet,and 1 pig per replicate.The results show that DE of ingredients among 7.42～21.65 MJ/kg DM,ME of ingredients among 6.86～20.69 MJ/kg DM.The calculated value of DE and ME of 10 validated diets were not significantly different from the measured value,and the linear regression model of the measured value to the calculated value overlaps with Y=X.It can be seen that the biological method to determine the DE and ME of feed ingredients has the additivity.Experiment three investigated the accuracy of the chemical analysis method to estimate the DE and ME of the feeds.The diets and ingredients in experiment three were the same as those in experiment two.Based on the chemical analysis method to estimate the prediction equation of ingredients referred to GB/T 39235-2020 nutrient requirements of swine,and diets prediction equation refer to Noblet(1993).The results show that the difference between use ingredients prediction equation to estimate DE and ME and the measured value among-2.17～1.93 MJ/kg DM and-3.27～2.11 MJ/kg DM;the difference between use diets prediction equation to estimate DE and ME and the measured value among-0.52～0.46 MJ/kg DM and-0.63～0.30 MJ/kg DM.It can be seen that it is difficult to obtain satisfactory results based on the chemical composition method to estimate the DE and ME of the raw materials and diets of growing pigs.Experiment four investigates the accuracy of the bionic digestion method in estimating DE and ME.The experiment based on the third-generation bionic digestive system horizontal digestion module to determine enzyme hydrolysate energy value(EHGE)of ingredients.And compare with the EHGE and DE and ME values obtained in experiment 2 to perform difference comparison and correlation analysis.The result showed that energy ingredients of EHGE to DE close to 1,EHGE to ME is greater than 1.The protein ingredients of EHGE to DE and ME were less than 1.The regression models of measured DE and ME of 20 feed ingredients on EHGE are:DE=0.9997×EHGE+0.706(R~2=0.8216,P<0.01),ME=1.0024×EHGE+0.0374(R~2=0.8685,P<0.01).The correlation coefficients between the DE and ME of the 10 validated diets estimated by the regression equation and the measured values of biological methods were 0.9494 and 0.9437,respectively.Therefore,the DE and ME of pig ingredients can be accurately estimated based on the bionic digestion method.In summary,0.8 g is the best sample size in the determination of pig feed GE;in addition,the bionic digestion method is more accurate than the chemical analysis estimate method to estimate the DE and ME of pig feeds.