Study On The Prediction Of Carbohydrate Digestibility In Diet By Applying CNCPS-S Sheep Model

The purpose of this study was to apply the rumen fermentation and intestinal digestion prediction model of Cornell sheep net carbohydrate and protein system(CNCPS-S)to predict the ruminal effective degradability(ED),intestinal digestibility of dietary carbohydrate(CHO)and rumen microbial protein(MCP)synthesis production of diets,and the accuracy of the model formula for predicting digestibility of dietary CHO in CNCPS-S system was verified by actual measurement.Experiment 1:Three Kazakh wethers with(38.03±1.56)kg body weight and permanent ruminal fistula were chosen and three kinds of total mixed diet(TMR)were designed of which the concentrate/roughage ratio were 30:70,35:65 and 40:60.The outflow rate(Kp)of ruminal digesta of 3 diets and ruminal ED of three kinds of dietary CHO were measured by the ruminal perfusion test and nylon bag test.Meanwhile,the CNCPS-S model formula was used to predict Kp of ruminal digesta of 3 diets and ED of CHO in 3 diets,and the predicted and measured values of ED of CHO in diets were analyzed by linear regression analysis so as to evaluate the accuracy of the model prediction.The results showed that:The average deviation between the predicted and measured values of ruminal ED of CHO in 3 diets was relatively small(mean deviation?4 g/100 g CHO),the mean deviation between the CHO ED and the measured values was the least,and there was a high correlation between the ED values and the measured values in the diets of each group(R~2?0.86),the root mean square error was also lower(RMSE?1.93 g/100 g CHO).It is concluded that the CNCPS-S rumen degradation prediction model is the most accurate prediction of rumen ED for CHO in high concentrate diets,and also has a good prediction ability for rumen ED in low concentrate diets.Experiment 2:Using 3×3 Latin design,three Kazak rams with mean weight of(45.08±1.91)kg and surgical installation of rumen fistula and proximal duodenal fistula were selected as test animals.The duodenal microbial protein(MCP)synthesis and rumen fluid pH of sheep with three different concentrate/roughage ratios were measured by in vivo method.The CNCPS-S ruminal fermentation model was used to predict the MCP synthesis of the three diets,and the accuracy of the model prediction was evaluated.The results showed that:1)the pH values of the 3 diets were 6.38~6.71,6.01~6.59 and 5.81~6.41,respectively,and the pH predicted by the model is a fixed value of 6.46;2)the three TMRs are all ruminal energy and nitrogen negative balance type,and ruminal energy nitrogen balance value was decreased significantly with the increase of concentrate levels(P<0.01).The conversion efficiency of MCP was the highest in TMR1 group;3)By linear regression analysis,the average deviation between the predicted values and the measured values of MCP of the three diets was larger(mean deviation?116 g/d),the mean deviation between prediction and measured value of high-concentrate MCP group is larger than that of low-concentrate group,the correlation of each group is especially low(R~2<0.75),and the RMSE was higher.It is concluded that the CNCPS-S has a good predictive ability for the rumen pH value of sheep in this area,the worst prediction results for MCP in the high concentrate group diet and the lower prediction ability for the other two groups.Experiment 3:The duodenal chyme,feces and urine was collected by the the second experiment in vivo method and were analyzed,and the intestinal digestibility of RECHO in diets,the whole digestive tract digestibility of CHO in diets and the DMI of sheep were determined.Combined with CNCPS-S model,the small intestinal digestibility of RECHO in 3diets and DMI of sheep was predicted and the accuracy of the model was evaluated.The results showed that:1)The apparent digestibility of DM,OM and nitrogen had no significant change with the increase of concentrate/forage ratios,but the intestinal digestibility of starch was increased with the increase of concentrate level(P<0.05).2)The average deviation between the predicted and measured values of DMI of sheep is small(mean deviation?0.15kg/d).Except for TMR2,the correlation among other groups is higher(R~2?0.68),and the RMSE is also low(RMSE?0.02 kg/d);The average deviation between the predicted and measured values of intestinal digestibility of RECHO in diets was relatively small(the average deviation?6.22 g/100 g RECHO),and the RMSE was also low(RMSE?6.03 g/100 g RECHO);The average deviation between the predicted and measured values of total digestive tract apparent digestibility of CHO in diets was relatively small(the average deviation?15.97g/100 g CHO),TMR1 group had the higher correlation(R~2?0.98),and RMSE of each group was also lower(RMSE?4.77 g/100 g CHO).The results showed that the prediction of sheep DMI by CNCPS-S model is basically acceptable,the small intestinal digestibility of RECHO and the apparent digestibility of whole digestive tract of CHO in high concentrate ratio diet are better,and the prediction of low concentrate group is basically acceptable.In summary,the model formula of CNCPS-S system is the most accurate to predict the digestibility of CHO in sheep high concentrate proportion diet,the prediction of low concentrate group is basically acceptable,the rumen pH value and DMI prediction result of sheep diet are acceptable,and the prediction ability of sheep MCP synthesis is poor.