Effect of Protein Fractionation and Buffer Solubility of Forage Sources on In Vitro Fermentation Characteristics, Degradability and Gas Production

Buffer solubility and protein fractionation were evaluated from the hays (timothy, alfalfa and klein) and straws (tall fescue and rice), and in vitro trial was conducted to examine the effect of buffer extraction on fermentation characteristics, degradability and gas (CO₂ and CH₄) production. Buffer soluble protein (SP) content and A fraction in total protein were highest in alfalfa hay as 61% and 41.77%, respectively while lowest in rice straw (42.8% and 19.78%, respectively). No difference was observed in B1 fraction among forages but B2 fraction was slightly increased in klein hay (12.34%) and tall fescue straw (10.05%) compared with other forages (6.34~8.85%). B3 fraction of tall fescue was highest as 38.49% without difference among other forages while C fraction was highest in rice straw. pH in incubation solution was higher in all forages after extraction than before extraction at 3h (P less than 0.01) and 6h (P less than 0.05), and pH from hays of timothy and alfalfa was higher than the other forages at 6h (P less than 0.05) and 12h (P less than 0.001). Regardless of extraction, ammonia-N concentration from alfalfa hay was increased at all incubation times and extraction effect was appeared only at 3h incubation time (P less than 0.01). Total VFA concentration from alfalfa hay was highest up to 24h incubation while those from tall fescue straw and rice straw were lowest. Buffer extraction decreased (P less than 0.01~P less than 0.001) the total VFA concentration. Acetic acid proportion was increased (P less than 0.001) before extraction of forages but no difference was found between forages. Propionic acid(C₃) proportion was also increased(P less than 0.001) before extraction in all forages than in straws at 3h, 24h and 48h incubations, and C₃ from hays were mostly higher (P less than 0.05) than from straws. Butyric acid proportion, however, was not affected by extraction at most incubation times. Parameter 'a' regarding to the dry matter (DM) degradation was increase (P less than 0.001) in all forages before extraction, and was decreased (P less than 0.05) in tall fescue straw and rice straw compared with hays. Parameter 'b' was also increased (P less than 0.001) before extraction but no difference was found between forages. Effective degradability of DM (EDDM) was higher (P less than 0.001) before extraction in most forages except for rice straw. Buffer extraction decreased (P less than 0.05) all parameters (a, b, and c) regrading to the crude protein (CP) degradation but no difference was found between forages. Effective degradation of CP (EDCP) was lower (P less than 0.05) in straws than in hays. Parameters 'a' and 'b' regarding to the NDF degradation (P less than 0.01) and effective degradability of NDF (EDNDF, P less than 0.001) were also higher in forages before extraction than after extraction but no difference was found between forages. Buffer extraction reduced (P less than 0.05~P less than 0.001) CO₂ production from all the forages uo to 24h incubation and its production was greater (P less than 0.05~P less than 0.01) from hays than straws. Methane (CH₄) production was also greater (P less than 0.01~P less than 0.001) in all forages at all incubation times, and its production was greater (P less than 0.05) from hays than from straws at most incubation times. Based on the results of the current study, it can be concluded that buffer solubility and CP fractionation might be closely related with in vitro VFA concentration, degradability and gas (CO₂ and CH₄) production. Thus, measurement of buffer solubility and protein fractionation of forages might be useful to improve TMR availability in the ruminants.