The use of cumulative gas and volatile fatty acid production to predict in vitro fermentation kinetics of Italian ryegrass leaf cell walls and contents at various time intervals

Abstract

Differences between the fermentation characteristics of cell contents (CC) and protease-treated cell walls (CW) of young leaves of Italian ryegrass (Loliurn rnultgorurn Lam.) cultivar Multimo (tetraploid), were studied in vitro. Gas and volatile fatty acid (VFA) production rates were measured at regular intervals, as was the degradability of organic matter (OM) of CW. The measured VFA were used to predict the gas production and fermentable OM using stoichiometric calculations. For CW the volume and kinetics of measured gas production were the same as those predicted from the VFA formed. In contrast, the measured gas production for CC was consistently less than predicted, indicating that the stoichiometric equations were not valid for rapidly fermenting substrates. For both CC and CW, the relative rate of acetic acid production levelled off more slowly than for other VFA, resulting in an increasing gas yield (in ml/g fermentable OM) after 12 (CW)-24 (CC) h incubation. Consequently, the fermentation of OM was not linearly related to gas production kinetics. For CW, the kinetics of decline of degradable OM and fermentable OM were the same, after correction for a constant 'lost fraction' of degradable OM of 205 g/kg OM. This work indicates the value of detailed studies of fermentation processes to evaluate herbage quality. In particular, the role of CC and the difference between degradation and fermentation require further attention.

Estimation of total volatile fatty acid (VFA) from total organic carbons (TOCs) assessment through in vitro fermentation of livestock feeds

“…Types of VFA affect the amount of CH 4 production; propionate decreases the overall gas production, but acetate linearly increased the gas production. Methane is produced mainly when the feed is fermented to acetate and butyrate, in contrast, relatively lower CH 4 gas production is occurred with propionate production (de Groot et al, 1998). Gas is produced mainly when feed materials are fermented to acetate and butyrate.…”

The influence of casein and urea as nitrogen sources on in vitro equine caecal fermentation

“…Microbial biomass was estimated using purine bases (adenine 1 guanine) as markers (Zinn and Owens, 1986). Data from VFA production and application of the stoichiometric theoretical equations (Demeyer, 1991;Van Soest, 1994;Groot et al, 1998) allowed the estimation of ATP production. For ATP production estimates, 1 mmol acetate (C 2 ) 5 2 mmol ATP, 1 mmol propionate (C 3 ) 5 3 mmol ATP (assuming that all propionate is generated by the succinate pathway), or 1 mmol propionate (C 3 ) 5 1 mmol ATP (assuming that all propionate is generated by the acrylate pathway), 1 mmol butyrate (C 4 ) 5 3 mmol ATP and 1 mmol methane 5 1 mmol ATP (Van Soest, 1994;Groot et al, 1998).…”

“…The molar proportions of CO 2 and CH 4 in the gas produced should be derived, as only acetate and butyrate account for direct gas production. From stoichiometric equations it can be calculated that CO 2 5 (C 2 /2) 1 (C 3 /4) 1 (3C 4 /2) and CH 4 5 C 2 1 2C 4 2CO 2 (Van Soest, 1994;Groot et al, 1998).…”

Influence of diet on growth yields of rumen micro-organisms in vitro andin vivo: influence on growth yield of variable carbon fluxes to fermentation products

“…Gravimetric methods measuring substrate disappearance have frequently been criticized on the grounds that substrate may be lost, for example by solubilization or filtration, without having actually being fermented (Menke et al 1979;Blümmel & Ørskov, 1993;Groot et al 1998;Pell et al 1998) and these concerns can be justified (see Fig. 5).…”