Use of an in vitro Rumen Gas Production Technique to Evaluate the Nutritive Value of Five Forage to Concentrate Ratios

This study presents the chemical composition and in vitro fermentation of five diets with different forage (alfalfa) to concentrate (faba bean) (F:C) ratios, F0:C100, F25:C75, F50:C50, F75:C25, F100:C0 on a dry matter (DM) basis. Results indicate that the chemical composition in term of organic matter (OM), ether extract (EE), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), neutral detergent insoluble protein (NDIP), acid detergent insoluble protein (ADIP) and total phenols (TPh), tannin (TT) and condensed tannin (TCT) were varies among five diets (P<0.05). After an initial gas test to evaluate 96 h gas production profiles of diets, the time to half maximal gas production was calculated and a second incubation was conducted with fermentation stopped at substrate specific half-time (t1/2) and 24 h for each substrate. In vitro true DM degradability (ivTDDM), OM degradability (ivOMD) were increased (P<0.01) by addition proportions of concentrate in diets. Microbial mass (g/kg DM), metabolizable energy (ME) (MJ/kg DM), were greater in diets which those had been higher degradability. The efficiency of microbial production (PF) (mg/mL) were calculated for both substrate specific t1/2 and 24 h and was not shown differences between experimental diets at 24 h but F100:C0 was lesser (1.17 mg/mL) at substrate specific t1/2 (P<0.01). Gas produced from fermentable fraction (B) and the rate of gas production (c) were (P<0.01) greater in diets with grater concentrate ratio. Increasing the F:C ratio increased ruminal pH and N ammonia and affected concentrations of short-chain fatty acid (SCFA) (P<0.01). Amount of CH4 emission from 13 to 17.16 g/kg DM and the great value was related to F100:C0.