The objective of this study was to evaluate the effects of the inclusion of País grape marc (GM) in high (HF) and low forage (LF) ruminant diets on rumen methane (CH₄) production and fermentation parameters in an in vitro (batch) culture. Experimental treatments replaced forage for GM at increasing concentrations (0, 10%, 20% dry matter [DM]) in the incubation substrates. Gas production (GP) and CH₄ production were measured at 6, 12 and 24 h of incubation and in vitro DM disappearance, volatile fatty acids (VFA) and ammonia nitrogen (NH₃-N) were determined at 24 h. The inclusion of 10% and 20% of GM reduced NH₃-N concentrations (p < 0.001) by 48% and 58% respectively, and GM₂₀ inclusion reduced BCVFA concentrations (p = 0.049) by 21% for HF and by 11% LF. Inclusion of 20% GM reduced the percentage of CH₄ in gas (p = 0.038), CH₄ production (p = 0.004) and CH₄ yield (p = 0.027), but leads to a reduction of in vitro dry matter disappearance (IVDMD) (p < 0.001), gas production (p < 0.001) and total VFA (p = 0.001). In conclusion, in batch culture conditions, partial substitution of fibre sources by País GM in high and low fibre diets has the potential to reduce NH₃-N concentrations and CH₄ production and yield with a reduction of IVDMD.

The aim of this study was to compare the effects of a pine (Pinus radiata D. Don) bark extract (PBE) with a quebracho (Schinopsis balansae Engl.) extract (QTE) on methane (CH₄) production and in vitro rumen fermentation parameters. A forage diet supplemented with PBE or QTE (0, 2 and 4% dry matter (DM) basis) was incubated for 24 h to determine in vitro DM disappearance (IVDMD), CH₄, volatile fatty acids (VFA), and ammonia nitrogen (NH₃-N) production. Differences were analyzed using Tukey’s test, orthogonal contrasts, hierarchical clustering heatmap (HCH), and principal component analysis (PCA). Both extracts (4% DM) decreased butyrate (Bu; p = 0.001), CH₄ (p = 0.005), total VFA (p < 0.001), and NH₃-N (p = 0.006) production and increased acetate (Ac; p = 0.003) without affecting the partitioning factor (p = 0.095). Propionate (Pr; p = 0.016) was increased, whereas IVDMD (p = 0.041) was decreased with QTE (4% DM). The inclusion of QTE (2% DM) decreased CH₄ production (p = 0.005) and the (Ac + Bu)/Pr ratio (p = 0.003), whereas PBE (2% DM) decreased the NH₃-N (p = 0.006) and total VFA production (p < 0.001). The HCH and PCA indicate a negative correlation (r = −0.93; p < 0.001) between CH₄ production and tannins. In conclusion, PBE shares many of the effects generated by QTE on ruminal fermentation, although the magnitude of these effects depends on concentration. The PBE could be used as an additive in ruminant diets to reduce CH₄ and NH₃-N production without reducing IVDMD or increasing propionate, but further in vivo studies are required to clarify its effects on animal production.

Forages and concentrates have consistently distinct patterns of fermentation in the rumen, with forages producing more methane (CH₄) per unit of digested organic matter (OM) and higher acetate to propionate ratio than concentrates. A mechanism based on the Monod function of microbial growth has been proposed to explain the distinct fermentation pattern of forages and concentrates, where greater dilution rates and lower pH associated with concentrate feeding increase dihydrogen (H₂) concentration through increasing methanogens growth rate and decreasing methanogens theoretically maximal growth rate, respectively. Increased H₂ concentration would in turn inhibit H₂ production, decreasing methanogenesis, inhibit H₂-producing pathways such as acetate production via pyruvate oxidative decarboxylation, and stimulate H₂-incorporating pathways such as propionate production. We examined the hypothesis that equalizing dilution rates in serial rumen cultures would result in a similar fermentation profile of a high forage and a high concentrate substrate. Under a 2 × 3 factorial arrangement, a high forage and a high concentrate substrate were incubated at dilution rates of 0.14, 0.28, or 0.56 h⁻¹ in eight transfers of serial rumen cultures. Each treatment was replicated thrice, and the experiment repeated in two different months. The high concentrate substrate accumulated considerably more H₂ and formate and produced less CH₄ than the high forage substrate. Methanogens were nearly washed-out with high concentrate and increased their initial numbers with high forage. The effect of dilution rate was minor in comparison to the effect of the type of substrate. Accumulation of H₂ and formate with high concentrate inhibited acetate and probably H₂ and formate production, and stimulated butyrate, rather than propionate, as an electron sink alternative to CH₄. All three dilution rates are considered high and selected for rapidly growing bacteria. The archaeal community composition varied widely and inconsistently. Lactate accumulated with both substrates, likely favored by microbial growth kinetics rather than by H₂ accumulation thermodynamically stimulating electron disposal from NADH into pyruvate reduction. In this study, the type of substrate had a major effect on rumen fermentation largely independent of dilution rate and pH.

This study was conducted to assess the effects of small supplemental doses of a polyphenolic extract from pine bark (PBE) on CH₄ output and ruminal fermentation parameters when incubated in batch culture with a high–concentrate diet for 24–h. The data from the dietary substrates supplemented with 0.0, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8% of PBE were evaluated in a randomized complete block design, and compared using ANOVA followed by Tukey's test and polynomial contrasts. Increasing doses of the PBE caused a linear decrease of the NH₃–N concentration (p < 0.001), the potentially degradable dry matter (DM) fraction (p = 0.002), the partitioning factor (p = 0.001), CH₄ production and proportion (p = 0.001 and p = 0.029, respectively), although only at 6–h, achieving the lowest productions (p = 0.016) with 1.5 and 1.8% PBE. In contrast, the PBE linearly increased asymptotic gas production (p = 0.007), gas yield (p = 0.004), pH (p = 0.002) and the short–chain fatty acid concentration (p < 0.001) at 24–h. Addition of least 1.5% PBE to high–concentrate diets reduces CH₄ production by 31% at 6–h, whereas NH₃–N concentration is reduced by 31% at 24–h incubations.