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Condensed tannins in plants are found free and attached to protein and fibre but it is not known whether these fractions influence degradation and rumen function. The aim of the study was to explore the rumen degradation of tropical tannins-rich plants and elucidate their relationship with the disappearance of condensed tannins fractions. The effects on fermentation parameters and microbial communities colonising plant particles in the rumen was also assessed. We used in situ and in vitro approaches to study four leguminous: leaves from Calliandra calothyrsus, Gliricidia sepium, and Leucaena leucocephala, Acacia nilotica pods and the leaves of two agricultural by-products: Manihot esculenta and Musa spp. Plants were analysed to quantify levels of hydrolysable tannins, free condensed tannins, protein-bound condensed tannins and fibre-bound condensed tannins. Rumen dry matter, nitrogen and fibre (NDF) degradability, rumen disappearance of tannin fractions and microbial colonisation of plants was assessed in situ. The methane-mitigation potential of tannin-rich plants compared to a tropical forage without tannins was assessed in vitro. All plants contained more than 100 g/kg of condensed tannins with a large proportion (32 to 61%) bound to proteins. Calliandra calothyrsus had the highest concentration of condensed tannins at 361 g/kg, whereas Acacia nilotica was particularly rich in hydrolysable tannins (350 g/kg). Hydrolysable and free condensed tannins from all plants completely disappeared after 24 h incubation in the rumen. Disappearance of protein-bound condensed tannins was more variable with Gliricidia sepium showing the highest proportion (93%), Manihot esculenta and Musa spp. showed intermediate values of disappearance, and no disappearance was observed from Calliandra calothyrsus leaves. In contrast, fibre-bound condensed tannins disappearance averaged ~82% and did not vary between plants. Disappearance of bound fractions of condensed tannins was not associated with degradability of plant fractions. Dry matter and nitrogen degradation were similar for all plants except Calliandra calothyrsus and Musa spp. that showed lower values. Calliandra and Acacia nilotica had also a lower NDF degradation. Methane production was also lower for these plants and for Leucaena leucocephala although for the latter total volatile fatty acids production was not affected and was similar to control. The presence of tannins interfered with the microbial colonisation of plants. Each plant had distinct bacterial and archaeal communities after 3 and 12 h of incubation in the rumen and distinct protozoal communities at 3 h. Adherent communities in tannin-rich plants had a lower relative abundance of fibrolytic microbes, notably Fibrobacter spp. Whereas, archaea diversity was reduced in high tannin-containing Calliandra calothyrsus and Acacia nilotica at 12 h of incubation. Here we show that the total amount of hydrolysable and condensed tannins contained in a plant govern the interaction with rumen microbes affecting degradability and fermentation. The effect of protein- and fibre-bound condensed tannins on degradability is less important.

The present study was carried out to determine the effect of Acacia nilotica, a tropical plant rich in hydrolyzable tannins (HT), on rumen fermentation and methane (CH4) production in vitro. We used leaves and pods from A. nilotica alone and combined. The combination of HT from A. nilotica leaves and pods and condensed tannins (CT) from Calliandra calothyrsus and Leucaena leucocephala were also evaluated to assess potential differences in biological activity between HT and CT. Four series of 24-h incubations were performed using rumen contents of 4 sheep fed a tropical grass (natural grassland based on Dichanthium spp.). A first experiment tested different levels of replacement of this tropical forage (control [CTL] without tannins) by A. nilotica leaves or pods: 0:100, 25:75, 50:50, 75:25 and 100:0. A second experiment tested the mixture of A. nilotica leaves and pods in different proportions: 100:0, 75:25, 50:50, 25:75, and 0:100. A third experiment tested the 50:50 combination of A. nilotica leaves or pods with C. calothyrsus and L. leucocephala. Acacia nilotica pods and leaves had a high content of HT (350 and 178 g/kg DM, respectively), whereas C. calothyrsus and L. leucocephala had a high content of CT (361 and 180 g/kg DM, respectively). The inclusion of HT from A. nilotica leaves and pods decreased CH4 production dose-dependently (P < 0.01). Total replacement of the CTL by A. nilotica decreased CH4 production by 64 and 55% with leaves and pods, respectively. Pods were richer in HT than leaves, but their antimethanogenic effect did not differ (P > 0.05). Although A. nilotica leaves and pods inhibited fermentation, as indicated by the lower gas production and VFA production (P < 0.01), this effect was less pronounced than for CH4. Volatile fatty acid production decreased by 12% in leaves and by 30% in pods when compared with the CTL alone. Positive associative effect was reported for VFA, when HT-rich sources and CT-rich sources were mixed. Combining the 2 sources of HT did not show associative effects on fermentation or CH4 production (P > 0.05). Hydrolyzable tannin-rich sources were more effective in suppressing methanogenesis than CT-rich sources. Our results show that HT-rich A. nilotica leaves and pods have the potential to reduce ruminal CH4 production.

The current study was carried out to determine the effect of secondary metabolites on in vitro rumen microbial fermentation and their potential to inhibit methane (CH4) production involved in the global warming and greenhouse-gases. The obtained results showed that the addition of Yucca schidigera and Quillaja saponaria reduced significantly CH4 production (P

The objective of this work was to study nutritional strategies for decreasing methane production by ruminants fed tropical diets, combining in vitro and in vivo methods. The in vitro approach was used to evaluate the dose effect of condensed tannins (CT) contained in leaves of Gliricidia sepium, Leucaena leucocephala, and Manihot esculenta (39, 75, and 92 g CT/kg DM, respectively) on methane production and ruminal fermentation characteristics. Tannin-rich plants (TRP) were incubated for 24 h alone or mixed with a natural grassland hay based on Dichanthium spp. (control plant), so that proportions of TRP were 0, 0.25, 0.5, 0.75, and 1.0. Methane production, VFA concentration, and fermented OM decreased with increased proportions of TRP. Numerical differences on methane production and VFA concentration among TRP sources may be due to differences in their CT content, with greater effects for L. leucocephala and M. esculenta than for G. sepium. Independently of TRP, the response to increasing doses of CT was linear for methane production but quadratic for VFA concentration. As a result, at moderate tannin dose, methane decreased more than VFA. The in vivo trial was conducted to investigate the effect of TRP on different ruminal microbial populations. To this end, 8 rumen-cannulated sheep from 2 breeds (Texel and Blackbelly) were used in two 4 × 4 Latin square designs. Diets were fed ad libitum and were composed of the same feeds used for the in vitro trial: control plant alone or combined with pellets made from TRP leaves at 44% of the diet DM. Compared to TRP, concentration of Ruminococcus flavefaciens was greater for the control diet and concentration of Ruminococcus albus was least for the control diet. The methanogen population was greater for Texel than for Blackbelly. By contrast, TRP-containing diets did not affect protozoa or Fibrobacter succinogenes numbers. Hence, TRP showed potential for mitigating methane production by ruminants. These findings suggest that TRP fed as pellets could be used to decrease methane production.

The objective of this work was to study nutritional strategies for decreasing methane production by ruminants fed tropical diets, combining in vitro and in vivo methods. The in vitro approach was used to evaluate the dose effect of condensed tannins (CT) contained in leaves of Gliricidia sepium, Leucaena leucocephala, and Manihot esculenta (39, 75, and 92 g CT/kg DM, respectively) on methane production and ruminal fermentation characteristics. Tannin-rich plants (TRP) were incubated for 24 h alone or mixed with a natural grassland hay based on Dichanthium spp. (control plant), so that proportions of TRP were 0, 0.25, 0.5, 0.75, and 1.0. Methane production, VFA concentration, and fermented OM decreased with increased proportions of TRP. Numerical differences on methane production and VFA concentration among TRP sources may be due to differences in their CT content, with greater effects for L. leucocephala and M. esculenta than for G. sepium. Independently of TRP, the response to increasing doses of CT was linear for methane production but quadratic for VFA concentration. As a result, at moderate tannin dose, methane decreased more than VFA. The in vivo trial was conducted to investigate the effect of TRP on different ruminal microbial populations. To this end, 8 rumen-cannulated sheep from 2 breeds (Texel and Blackbelly) were used in two 4 × 4 Latin square designs. Diets were fed ad libitum and were composed of the same feeds used for the in vitro trial: control plant alone or combined with pellets made from TRP leaves at 44% of the diet DM. Compared to TRP, concentration of Ruminococcus flavefaciens was greater for the control diet and concentration of Ruminococcus albus was least for the control diet. The methanogen population was greater for Texel than for Blackbelly. By contrast, TRP-containing diets did not affect protozoa or Fibrobacter succinogenes numbers. Hence, TRP showed potential for mitigating methane production by ruminants. These findings suggest that TRP fed as pellets could be used to decrease methane production.