معرفی مدل خطی تخمین انرژی قابل متابولیسم سورگوم علوفه‌ای با استفاده از اجزای الیاف

Introduction: The metabolizable energy represents a part of the gross energy of the feed, which after the deduction of the amount of feces and urine energy and the gases. One of the laboratory methods for determining the metabolizable energy of feedstuff is the gas method. This method is based on the measurement of the amount of released gas at the specified time. The estimated energy obtained from this method has a very high correlation with the amount of energy derived from the live animal method (in vivo). The direct determination of the energy available of feeds requires a great deal of time and cost, and since the available energy has a positive and high relationship with some of the chemical constituents of the feed, livestock nutritionists use fiber components such as NDF, ADF and lignin to estimate the available energy of feeds. Another approach is using equations to obtain the ADF for metabolizable energy of forages. It was reported that the amount of determination coefficient (R²) for estimating the metabolizable energy of forages from ADF levels was from 0.52 to 0.92. This study conducted to determine the nutritional value and introduce regression equations for estimating the available energy of some forage sorghum.
 
 Materials and Methods: Eighteen sorghum varieties planted in May 2016 at the research and educational farm in Karaj province of IRAN. Experimental varieties were harvested in September. Three samples of each sorghum forage cultivar, which planted in three separate rows, after crushing into 3 to 5 cm pieces, totaling about 54 samples, collected. Nutrient compositions including crude protein, crude ash, ADF, NDF, water-soluble carbohydrates, starch and lignin analyzed by AOAC official methods. The amount of crud ash determined by burning samples in an electric furnace and crude protein. To determine the concentration of ADL and to dissolve cellulose present in ADF, ADF samples placed in 72% sulfuric acid for three hours. The digestibility of the samples determined by gas test method. The amount of ME calculated using the volume of gas produced from fermentation of 200 mg of dry matter over a period of 24 hours. ME = 2/2 + 1357/0 (GP) + 0057/0 (XP) + 00002859/0 (XP) ² , Where ME is the metabolizable energy (MJ per kg of dry matter), GP, the volume of produced gas (ML in 200 mg dry matter per 24 hours incubation) and XP, crude protein (g / kg dry matter). For fitting the equations for estimating metabolizable energy based on NDF, ADF and lignin, SPSS software used to fit the linear, quadratic and exponential equation, and selected the independent variable that had the best R².
 
Results and Discussion: The average dry matter of total 54 experimental samples is 19.54, and it is less than minimum required for high-grade silage (25%). The amount of sugar and starch are enough, which is an important part for the preparation of stable and quality silage. Determined metabolism energy was 2.40, which is higher than that announced by researchers, which could be the reason for the presence of BMR hybrids in this experiment. The mean of NDF, ADF, lignin and metabolizable energy of forage sorghum was determined to be 60.36, 31.16, 1.78 and 2.40, respectively. The whole equations obtained from NDF, ADF, lignin had an acceptable coefficient of determination, but the equations obtained from the ADF value, as an independent factor, have a higher coefficient of determination and the accuracy of the equations is moderate and acceptable. Among the equations, the linear equation derived from ADF suggested for estimating metabolizable energy due to the simplicity and approximation closer to actual ME of forage sorghum measured. Compared to the international linear equations, which ADF were independent factor, the Menke and Steingas metabolizable energy from ADF equations do not have any significant difference with the estimated ME of forage sorghum in this study.
Conclusion: The results of chemical analysis and determination of ME of sorghum by gas test showed that the amount of ADF and ME of sorghum was 31.16% and 2.41 Mcal/kg of dry matter, respectively. The best correlation for estimating ME, which ADF was as independent factor, was the following proposed linear equation. ME (Mcal/Kg DM) = 3.320 - 0.029 (ADF %).