Structural features of condensed tannins affectin vitroruminal methane production and fermentation characteristics

Abstract

SUMMARYAn in vitro study was conducted to investigate the effects of condensed tannin (CT) structural properties, i.e. average polymer size (or mean degree of polymerization), percentage of cis flavan-3-ols and percentage of prodelphinidins in CT extracts on methane (CH4) production and fermentation characteristics. Condensed tannins were extracted from eight plants in order to obtain different CT types: blackcurrant leaves, goat willow leaves, goat willow twigs, pine bark, redcurrant leaves, sainfoin plants, weeping willow catkins and white clover flowers. They were analysed for CT content and CT composition by thiolytic degradation, followed by high performance liquid chromatography (HPLC) analysis. Grass silage was used as a control substrate. Condensed tannins were added to the substrate at a concentration of 40 g/kg, with or without polyethylene glycol (+ or −PEG 6000 treatment) to inactivate tannins, then incubated for 72 h in mixed buffered rumen fluid from three different lactating dairy cows per run. Total cumulative gas production (GP) was measured by an automated GP system. During the incubation, 12 gas samples (10 µl) were collected from each bottle headspace at 0, 2, 4, 6, 8, 12, 24, 30, 36, 48, 56 and 72 h of incubation and analysed for CH4. A modified Michaelis-Menten model was fitted to the CH4 concentration patterns and model estimates were used to calculate total cumulative CH4 production (GPCH4). Total cumulative GP and GPCH4 curves were fitted using biphasic and monophasic modified Michaelis-Menten models, respectively. Addition of PEG increased GP, GPCH4, and CH4 concentration compared with the −PEG treatment. All CT types reduced GPCH4 and CH4 concentration. All CT increased the half time of GP and GPCH4. Moreover, all CT decreased the maximum rate of fermentation for GPCH4 and rate of substrate degradation. The correlation between CT structure and GPCH4 and fermentation characteristics showed that the proportion of prodelphinidins within CT had the largest effect on fermentation characteristics, followed by average polymer size and percentage of cis flavan-3-ols.

Browse species from Ethiopia: role in methane reduction and nematode control in goats

“…The effect of tannins on GP is through substrate deprivation or enzyme activity inhibition in rumen microbes. The effect of PA on fermentation is more pronounced with PA containing more PD monomeric units (Huyen et al, 2016;Lowry et al, 1996). All PA-containing browse in the present experiment with the exception of D. angustifolia contained PD, indicating that the GP and CH 4 depressing effect partly originated from PD activity.…”

“…Within the HT sources, comparing commercial tannic acid and gallotannins in fireweed flowers, tannin-protein complex was strong for fireweed due to the larger molecular weight compared to tannic acid (Hagerman et al, 1992). The PD:PC ratio contributes most to the variation in in vitro CH 4 reduction potential of different tannin sources (Huyen et al, 2016). Monomers of PD were more potent inhibitors of in vitro larval exsheathment of Haemonchus contortus and Trichostrongylus colubriformis than monomers of PC (Brunet and Hoste, 2006).…”

“…Hydrolysable tannins have direct inhibitory effects on microbes, while CT act through reduction of fiber digestion with a subsequent lower CH 4 production . Within the CT group, differences in monomeric units and structure determine the magnitude of CH 4 reduction in vitro (Hatew et al, 2014;Huyen et al, 2016).…”

“…It may also suggest that PA is more correlated with effects on the rate of fermentation. Huyen et al (2016) reported that PA extracts added to grass silage (4%) decreased the rate of in vitro substrate degradation. Methane was markedly reduced and the percent increase after PEG addition ranged from 53% in E. racemosa to 601% in A. etbaica.…”

“…Variability in CH 4 reduction within HT (0.3-3.4%) and CT (1.1-5.7%) sources, was reported (Pellikaan et al, 2011b). Condensed tannin composition specifically prodelphinidin:procyanidin (PD:PC) ratio and degree of polymerization were key factors in differences in in vitro CH 4 suppressing effects of Onobrychis viciifolia (Hatew et al, 2016;Huyen et al, 2016). Polyphenol groups other than tannins have also CH 4 mitigating properties.…”