Metabolizable energy of roughage in Taiwan

The fixed metabolizable energy (ME) values from the NRC do not represent the true ME values of the various feedstuff used in livestock rations. Therefore, a rapid and effective method for evaluating the ME value of forage crops is required for proper ration formulation to improve production efficiency. Dairy goat digestion trials were conducted as the in vivo reference using the method of Menke and Steingass (1988) [Menke, K.H., Steingass, H., 1988. Feed Sci. Technol. 28, 91-97] which derived the amount of gas produced from in vitro fermentation. This method was adapted in this study to evaluate the ME value. In the goat digestion trial, six dairy goats were used for each roughage sample in a total fecal collection trial to determine the digestible nutrients, including energy (DE) and total digestible nutrient (TDN). The in vivo ME value was calculated using the method of Shiemann et al. (1971) [Shiemann, R., Nehring, K., Hoffmann, L., Jentsch, W., Chudy, A., 1971. Energetische Futterbewertung und Energienormen. VEB Deutscher Land-wirtschaftsverlag, Berlin, p. 75. (in German)] (ME(1) (MJ/kg)=5.2DCP+34.2DEE+12.8DCF+15.9DNFE, g/g). The in vitro ME value was then estimated from the chemical composition of the feed and amount of gas produced (G(b)) from in vitro fermentation. The value calculated from both with (ME(3)) and without (ME(2)) the inclusion of nitrogen free extracts (NFE) in the prediction equation. (ME(2) (MJ/kg)=0.145G(b)+4.12CP+6.5CP(2)+20.6EE+1.54, g/g; ME(3) (MJ/kg)=0.118G(b)+8.75CP+19.21EE+3.38NFE+0.691, g/g). The 12 roughage samples consisted different growth stages of Napier grass Taishi No. 2: (day of harvest; 40, 50, 60 and 65), dwarf Napier grass Taishi No. 1: (Day 40 and 65) and Pangola grass (Day 45) hay (Day 70), corn silage, imported alfalfa hay, timothy hay and Bermuda hay. The correlation between the ME values calculated from in vivo and in vitro without NFE was lower than with NFE inclusion in the equation. A higher correlation between the ME values calculated from in vivo and in vitro without NFE inclusion than with NFE inclusion in the prediction equation was obtained when alfalfa and corn silage were not included. This indicated that the ME value of forage could be estimated rapidly using this in vitro gas method adapted from Menke and Steingass (1988) [Menke, K.H., Steingass, H., 1988. Feed Sci. Technol. 28, 91-97] for practical applications in ration formulation.