In vitro screening of the potential of numerous plant species as antimethanogenic feed additives for ruminants

A screening experiment was conducted to evaluate the potential of 450 plant species as antimethanogenic additives in ruminant feeds. Effects of addition of these plants, which were incorporated to the fermentation substrate as a dry powder, on ruminal fermentation, fibre digestion and methane production were studied in vitro in batch cultures of mixed rumen microorganisms. Serum bottles containing 500 mg of substrate (500 g alfalfa hay/kg, 400 g grass hay/kg and 100 g barley grain), 50 mg of the plant additive tested and 50 ml of buffered rumen fluid (10 ml sheep rumen fluid + 40 ml culture medium) were incubated at 39 °C for 24 h. After incubation, gas and methane production, pH and volatile fatty acid (VFA) concentration in the incubation medium and dry matter and neutral detergent fibre disappearance were recorded. Of the 450 samples tested, 35 decreased methane production by more than 15% versus those with corresponding control cultures and, with 6 of these plant additives, the depression in methane production was more than 25%, with no adverse effects on digestibility, total gas and VFA production. With these six samples, incubations were repeated to confirm their effects on methane production in vitro. Some candidates, in particular Rheum nobile and Carduus pycnocephalus, consistently decreased methane production without adversely affecting other parameters of the rumen fermentation.