The objective of the current research was to evaluate the fermentative characteristics of silage made with the upper third section of cassava (Manihot esculenta) plants with added condensed tannin levels of 0, 25, 50 and 75 g/kg dry matter (DM). The experimental design was a complete randomized design, with treatments arranged in a 4 × 7 factorial (tannin addition levels × days of ensiling). The loss of gas and the presence of moulds observed in the opening days had increased linearly. Fermentative characteristics were decreased by the addition of tannin. Acetic acid content showed a linear increase. Tannin levels had a quadratic effect on gas production at 28 days of ensiling. After 56 days, however, tannin levels had no significant effect on silage gas production. After 28 days of ensiling, the degradability of potentially degradable fraction ‘b’ demonstrated quadratic effect. The same occurred with the fractions ‘a’, ‘b’ which were undegradable after 56 days of ensiling. The addition of condensed tannin lengthened the fermentative stage and caused the silage to stabilize after 56 days of ensiling.

Understanding the interactions between hydrogen producers and consumers in the rumen ecosystem is important for ruminant production and methane mitigation. The present study explored the relationships between rumen protozoa, methanogens and fermentation characteristics. A total of six donor sheep harbouring (F, faunated) or not (D, defaunated) protozoa in their rumens (D animals were kept without protozoa for a period of a few months (D − ) or for more than 2 years (D+)) were used in in vitro and in vivo experiments. In vitro the absence of protozoa decreased NH3 and butyrate production and had no effect on methane. In contrast, the liquid-associated bacterial and methanogens fraction of D+ inocula produced more methane than D −  and F inoculum (P < 0·05). In vivo fermentation parameters of donor animals showed the same trend on NH3 and butyrate and showed that D+ animals were high methane emitters, while D −  were the lowest ( − 35 %). The concentration of dissolved dihydrogen measured after feeding followed the opposite trend. Methane emissions did not correlate with the relative abundance of methanogens in the rumen measured by quantitative PCR, but there was a trend for higher methanogens concentration in the solid-associated population of D+ animals compared with D −  animals. In contrast, PCR-denaturing gradient gel electrophoresis profiles of methanogens' methyl coenzyme-M reductase A gene showed a clear clustering in liquid-associated fractions for all three groups of donors but fewer differences in solid-associated fractions. These results show that the absence of protozoa may affect differently the methanogen community and methane emissions in wethers.

Bromochloromethane (BCM), a halogenated methane analogue, was evaluated for its anti-methanogenic activity in both batch and continuous fermentation systems. For batch fermentation, a roughage-based substrate was incubated with mixed rumen microflora for 24 h at two concentrations of BCM (5 and 10 μm). A 89–94 % reduction in methane was obtained in terms of volume and truly degraded substrate (TDS; P < 0·05). The partitioning factor (an index of efficiency of microbial protein production; expressed as mg TDS/ml net gas produced) increased from 3·55 to 3·73 (P < 0·05), while the acetate:propionate proportion decreased from 2·80 to 2·22 (P < 0·05). A complete inhibition of methanogens was associated with a 48 % decrease in Ruminococcus flavefaciens, a 68 % increase in Fibrobacter succinogenes and a 30 % increase in rumen fungi when quantified using qPCR. The continuous fermentation was carried out using the roughage-based substrate in four fermenters, two fermenters being control and the other two fed with BCM (5 μm) once in a day, for nine consecutive days. A persistent effect of BCM on methane reduction (85–90 %) was obtained throughout the study (P < 0·05) with no effect on gas production, SCFA production, acetate:propionate proportion, true degradability and efficiency of microbial mass synthesis (P>0·05). The complete inhibition of methane resulted in a significant decrease in R. flavefaciens and methanogens (P < 0·05) and an increase in fungal population (P < 0·05), while there was no effect on total bacterial and F. succinogenes populations (P>0·05). The batch fermentation confirms the anti-methanogenic activity of BCM, while the continuous fermentation indicates the persistency of this effect under in vitro conditions.