Study On Protein Digestibility Prediction Model Of Sheep Fed Total Mixed Ration

Objective:The purpose of this experiment was to study the protein composition characteristics of three kinds of TMR by using Cornell Net Carbohydrate and Protein System for Sheep(CNCPS-S),and to predict the digestibility of TMR protein in the gastrointestinal tract of sheep.Finally,The accuracy of the system model was verified by rumen nylon bag method,in vitro three-step method and in vivo method.Method:(1)Three kinds of TMR with different ratio of concentrate to roughage(30:70,35:65,40:60,respectively)were prepared from feed samples collected in Xinjiang.The conventional nutrients of TMR were determined.The formula of CNCPS-S was used to calculate rapidly degradation of true protein(PB1),medium speed degradation of protein(PB2),slow degradation of true protein(PB3),non protein nitrogen(PA)and unavailable protein(PC).(2)Three kazakh castrated rams with weight of 38.03±1.56 kg and permanent rumen fistula were selected as experimental animals,the rumen dynamic degradation rate of three TMR protein components was determined by nylon bag method,the rumen degradation rate of protein components(Kd)was estimated by the least square method,and the outflow rate of rumen digesta(Kp)of three TMRS was measured and predicted.Finally,the applicability of the model of protein rumen degradation was verified.(3)Three kazakh castrated rams with permanent rumen fistulas were selected as experimental animals.The least square estimation of intestinal digestibility coefficients(Pb)of three TMR protein components was carried out by nylon bag method and three-step method in vitro.The CNCPS-S was used to predict the CP intestinal digestibility and CP total digestive tract digestibility of TMR.(4)three Kazakh castrated rams with duodenal fistula were selected as experimental animals.The 3×3 Latin square design was used to measure the CP intestinal digestibility and CP total digestive tract digestibility of TMR(the ratio of fine to coarse was 30:70,35:65 and 40:60,respectively).Finally,the linear regression analysis of the predicted and observed values was carried out to evaluate the accuracy of the model prediction.Results: Experiment 1: The results showed that the DM content of the three TMRS was about93%,and the DM content of TMR3 was the highest(P<0.01).The content of ADF was between32% and 38%,and TMR1 was significantly higher than TMR2 and TMR3(P<0.01).The content of NPN/SOLP ranged from 50.31% to 67.21%,and the content of ADFIP/CP ranged from 3.31%to 7.84%,indicating that the content of TMR1 was significantly higher than that of the other two groups(P<0.05).The PA and PC components of TMR1 were significantly higher than those of the other two groups(P<0.05).The PB1 of TMR3 was significantly higher than that of TMR1 and TMR2(P<0.01).Experiment 2: The results showed that the predicted values of outflow rate of rumen digesta of TMR1 and TMR2 were significantly lower than the observed values(P<0.05);There was no significant difference among the three TMRs in rumen effective degradationrate(P>0.05),and the difference between the predicted values of the rumen degradation rate was significantly(P<0.01),which was TMR1>TMR3>TMR2;The improved rumen degradation model of protein showed that the mean deviation between the predicted value and the observed value was low;the correlation coefficient ranged from 0.55 to 0.84;the slope was close to 1;and the RMSE was low.Experiment 3: After modifying the prediction equation of intestinal digestibility coefficient(pb1,pb2,pb3,pc),pb1 and pb2 of three TMRs were 100.00%,the fitting range of pb3 was 73.72% ～ 83.11%,and the range of pc was 18.64% ～ 32.28%.Based on this,it was predicted that there was no significant difference in CP digestibility among the three TMRs(P > 0.05),and the CP digestibility in total digestive tract of TMR1 and TMR2 was significantly higher than that of TMR3(P<0.05).Experiment 4: The results showed that: there was no significant difference in CP intestinal digestibility among the three TMRs(P>0.05),but the CP digestibility in total digestive tract of TMR1 and TMR2 was significantly higher than that of TMR3(P<0.05);the correlation coefficient between predicted values and observed values of CP intestinal digestibility of three TMRs was higher(between 0.873 and 0.976),RMSE was lower(between 0.59 and 7.19),and the determination coefficient was higher(between 0.652 and 0.952).Conclusion: CNCPS-S can accurately reflect the nutritional value of protein components in the total mixed ration.After improving the model,CNCPS-S can accurately predict the rumen degradation rate,intestinal digestion rate and total digestive tract digestion rate of CP in sheep.