Prediction Models Of The Metabolizable Energy Content Of Roughages Commonly Fed To Mutton Sheep

This study aimed to improve the nutritional database of roughages for mutton sheep. Ten roughages commonly fed to mutton sheep in China were selected as the research object. The Sable open circuit gas metabolism system was used to measured methane production. Based on the comprehensive comparison of metabolizable energy(ME) of roughage materials, the ME content of 10 roughages was determined and prediction equation was established. The present study included 3 trials as described as follows.Experiment 1 aimed to investigate methods and to determine the optimum substitutional proportion of single roughag used to estimate ME. Thirty crossbreed rams were used according to a randomized block design. The rams were divided into five treatments: diet based on full leymus chinensis, diet with a forage: concentrate ratio of 50:50. Each experiment period including 10 d of adaptation period. The 6d in a digestibility trial and methane was measured for 3d using open-circuit respirometry. The results showed that. The whole gut apparent digestibility of CP and NDF had no difference between direct and substitution methods. The digestibility of DM, OM, and GE of diet based on full leymus chinensis measured with direct method was higher than that of group 40%(P<0.05), but had no difference with group 20% and 40%(P>0.05). The DE measured in diet based on full leymus chinensis was significantly higher than that in group 60%(P<0.05), but had no difference with that measured in group 40% and group 20%(P>0.05). The ME measured in diet based on full leymus chinensis was higher than that measured in group 60%(P<0.05),and had no difference with that measured in 40% group and group of 20%. A significant difference was observed in the determined ME of leymus chinensis using different methods. The optimum substitution ratio was 20%.Experiment 2 aimed to investigate the feasibility to use the substitution methods to determine the ME content of peanut vines hay and its optimal substitution ratio in the diets of mutton sheep. Experiment animals same as experiment 1 were used according to a randomized block design. The wethers were divided into nine treatments randomly: the control group was fed a basal diet, and the other 8 groups were fed diets with different substitution ratio of the peanut vines hay(10%, 20%, 30%, 40%, 50%, 60%, 70%, and 100%, respectively).the animal was same as experiment 1. The results showed that no significant differences were found in DM digestibility among 20%, 30%, 40% and 100% substitution groups(P>0.05), while it was significantly higher in 100% group than other groups(P<0.01); The digestibility of OM of 100% group had no difference compared with that of group 20%(P>0.05), but was significantly higher than other groups(P<0.05). The digestibility of GE, CP, NDF, ADF, and EE were different between 100% and 10% groups(P<0.01), but no difference among other treatments was observed(P>0.05); The DE of peanut vines hay and calculated ME values were significantly different among treatments(P<0.01), and the values of DE and ME in 100% group was significantly higher than those of 50%, 60%, 70%, and 10% group(P<0.01), while no difference was observed among 20%, 30%, and 40% group(P>0.05); A significant difference was observed in the determination of nutrients and gases metabolism of peanut vines hay by using different substitution ratios. The optimum substitution ratio was 20% by using the substitution method to calculate the ME of peanut vines.Experiment 3 was based on the previous experiment 1 and 2 and the optimum substitution ratio, and available energy contents of 10 roughages commonly used for mutton sheep were predicted from nutrient digestibility. Nutrients digestibility, DE and ME of 10 roughages were measured in the substitution method. The optimal prediction paramteters were selected and predicting equations for DE and ME established based on the results of nutrient composition and digestibility, The results showed that the nutrient digestibility and available energy contents were significantly different among the 10 roughages(P<0.01). Digestibility of DM, OM, GE, CP and NDF were positively related to the composition of DM, OM, GE, CP. DDM, DOM and DP(P<0.01), but negatively related to that of NDF, ADF and DNDF(P<0.01). The DE and ME had positive relationship with DM, OM, GE and CP(P<0.01), but were negatively related to NDF and ADF(P<0.01). These results indicated that there were significant correlations between nutrient composition of single roughage and DE or ME. Thus the nutrient digestibility and available energy contents of roughages could be predicted based on their nutrient composition. The prediction equations of ME based on nutrient composition were as follows: ME(MJ/kg DM) =13.890-0.037DNDF(g/kg DM)+0.021DP(g/kg DM)+0.010DDM(g/kg DM)-0.008DOM(g/kg DM)(R2=0.993, n=60, P<0.01) and ME(MJ/kg DM) =-6.943-0.101NDF(%)+0.704GE(%)-0.101ADF(%)+0.138OM(%)+0.032CP(%)(R2=0.994, n=60, P<0.01).