Abstract: The purpose of this study was to predict the ruminal effective degradability (ED) of dietary carbohydrate (CHO) by Cornell sheep net carbohydrate and protein system (CNCPS-S) and was measured to verify the accuracy of the predicted values of the CNCPS-S model.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,respectively.The outflow rate (Kp) of ruminal digesta 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 was used to predict Kp of ruminal digesta and ED of CHO in three TMRs,and the predicted and measured values of ED of CHO were analyzed by linear regression analysis so as to evaluate the accuracy of the model prediction.The results showed that:The Kp of ruminal digesta of three kinds of TMR increased sequentially with the proportion of concentrate (P<0.01),which were 3.58%/h,3.83%/h and 4.05%/h,respectively.And the ruminal ED of dietary CHO based on these calculations were 42.7%,43.1% and 42.3% (P>0.05),respectively.The model predictive values of ruminal digesta Kp in three TMRs were increased with the increase of concentrate proportion,which were 1.62,1.63 and 1.64%/h (P>0.05),respectively.The predicted values of ruminal ED of dietary CHO were 39.5%,39.1% and 39.6% (P>0.05),respectively.The average deviation between the predicted and measured values of ruminal ED of three dietary CHO was relatively small (mean deviation ≤ 4 g/100 g CHO),and the correlation was high (R² ≥ 0.86),the root mean square error was also lower (RMSE ≤ 1.93 g/100 g CHO).It was concluded that the prediction model of ruminal degradation in CNCPS-S had a good predictive ability for the ruminal effective degradability of dietary CHO.

Key words: CNCPS-S; carbohydrate; outflow rate; ruminal degradability; sheep