In vitro fermentation of fodder beet root increases cumulative gas production of methane and carbon dioxide

Abstract

The relationship between proportion of fodder beet root (FB: Beta vulgaris subsp. vulgaris L.) in a perennial ryegrass (Lolium perenne) diet and gas production was investigated in vitro. Cumulative gas production and fermentation products were measured in calibrated glass syringes using a factorial arrangement (4 x 6), of dry matter proportion of FB (0, 15, 35 and 50% DM: 0FB, 15FB, 35FB and 50FB, respectively), and incubation time (0, 2, 4, 8, 12 and 24 h). Concentrations of methane (CH₄) and carbon dioxide (CO₂) produced both in fermentation and from bicarbonate buffering of volatile fatty acid, were also calculated. The proportion of FB root linearly increased volume of gas (mL) produced per g dry matter (DM) and per g organic matter (OM) with gas accumulation 14.8% greater for 50FB compared to 0FB at 24-hours of incubation (P<0.001). The concentration of propionic and butyric acids also increased relative to the proportion of FB (P < 0.001). Stoichiometric calculations indicate that FB increased CO₂ released from both buffering and fermentation processes but reduced the fractions of methane in gas (17.6, 17.4, 17.0 and 16.8 ± 0.4% for 0FB, 15FB, 35FB, and 50FB, respectively, P< 0.001). However, the greater OM content of FB increased the total volume of both CO₂ and CH₄ produced. Results suggest that FB altered the thermodynamics of fermentation early in digestion by increasing formation of propionate which acted as a hydrogen sink to reduce formation of methane. However, as fermentation progressed, butyrate forming pathways became more favourable. The greater OM content of FB compared to ryegrass increased absolute volumes of CO₂ and CH₄ from fermentation, resulting in greater emission of gasses per kg DM of substrate. Further investigation in vivo is required to determine potential effects of microbial protein synthesis on gas production and further verify these results.