Study On The Establishment Of Prediction Models Of Metabolizable Energy Of Concentrate For Mutton Sheep

The metabolizm of concentrate feedstuffs for sheep was investigated by the substitution method and in vivo method in this study. The metabolizable energy(ME) content of ingredients and compound feeds of concentrates was predicted from proximate analysis measurments and digestible nutrients in sheep.Exp. 1 aimed to investigate the practicability of estimating the ME value of grains and protein feeds by using the substitution method. Fifty-four castrated Dorper × thin-tailed Han crossbred rams(48.3 ± 1.3 kg of bodyweight) were randomly divided into 9 groups and fed one of the following nine experimental diets: a basal diet and 8 diets with increasing substitutional proportion of wheat. Digestibility and respirometry trials were conducted to measure digestible energy(DE) and ME, and to determine the appropriate substitution ratio of wheat. The results showed as follows: 1) With the increasing substitution ratio of wheat, the apparent digestibility of nutrients, urine energy, DE and ME were increased, whereas the fecal energy was decreased; 2) The apparent digestibility of gross energy, dry matter, organic matter and crude protein in wheat calculated by the substitutional method was not affected by treatment(P>0.05); 3) When the substitutional proportion was in the scale of 29% ~ 47%, the DE and ME of wheat were 14.55 and 11.86 MJ/kg, respectively. They were most similar to 14.52 MJ/kg as recommended by NRC(2007) and 11.91 MJ/kg calculated from the empirical equation(DE × 0.82). In conclusion, the appropriate substitutional ratio for ranged from 29 to 47%.Exp. 2 was conducted to evaluate the feasibility of the establishment of prediction equations for the ME of concentrate using proximate analysis measurements and digestible nutrients. Sixty-six castrated Dorper × thin-tailed Han crossbred rams(49.6 ± 1.3 kg of bodyweight) were randomly assigned into 11 groups. Digestibility and respirometry trials were conducted to measure and calculate dietary ME concentrations from proximate analysis measurements or digestible nutrients. The results showed as follows: GE(P <0.05), ADF(P <0.05), and OM(P <0.01) had significant correlations with DE. The proximate analysis measurements had no correlation with ME. Digestible nutrients and DE had significant correlations with ME, and the equation was: ME(MJ/kg)=1.344DE(MJ/kg)+1.321DDM(%)-5.347DOM(%)-2.093DADF(%)-1.907(R2=0.845, n=60, P <0.01), or ME(MJ/kg)= 1.349DE(MJ/kg)-6.577DOM(%)-2.105(R2=0.842, n=60, P <0.01). In conclusion, it was unsuitable to predict dietary ME content of individual energy and protein feeds by using the proximate analysis measurements, while it was accurate to predict ME using the digestible nutrients and DE.Expt. 3 conducted to evaluate the feasibility of the establishment of the dietary ME compound feeds of sheep by using proximate anlaysis measurements or digestible nutrients. Sixty-six castrated Dorper × thin-tailed Han crossbred rams(49.6 ± 1.3 kg of bodyweight) were randomly assigned into 11 groups. Digestibility trials were conducted to measure and calculate individual DE and ME, establishing the metabolic energy and proximate nutrients and digestible nutrient prediction model with the linear regression method. Results indicated that: the OM and GE digestibility of diets were highly significantly different from CP, NDF and ADF(P<0.01); CP digestibility was highly significantly different from CP, NDF and ADF(P<0.01), and significantly different from OM(P<0.05); NDF and ADF digestibility were highly significantly different from GE and CP(P<0.01). NDF digestibility was significantly different from OM and NDF(P<0.05). The prediction equation of dietary ME using proximate analysis measurements: ME(MJ/kg) = 38.881- 19.516ADF(%)- 28.672OM(%)(R2 = 0.640, n = 60, P<0.01); The prediction equation of dietary ME using digestible nutrients was ME(MJ/kg) = 1.613DE(MJ/kg)- 14.705DOM(%) + 2.743DNDF(%)- 3.179(R2 = 0.879, n = 60, P<0.01). In conclusion, there were significant correlations between proximate nutrients, digestible nutrients and ME. The prediction model of proximate nutrients and digestible nutrients can be used in routine analysis.In summary, it was feasible to determine the ME content of ingredients or compound feeds of concentrates for sheep by the substitution method. The proximate analysis measurements of compound diets were not relevant to dietary ME when the substitutional ratio exceeded 30%. Digestible nutrients predicted digestibility effectively; the proximate analysis measurements of the compound diets were relevant to digestibility and available energy of feedstuffs. The availability of energy and digestibility of feedstuffs could be predicted by proximate analysis measurements and digestible nutrients effectively.