Effect of tannin-rich forages on in vitro ruminal fermentation and methane production

Methane produced during anaerobic fermentation in the rumen not only affects the efficiency of energy utilization by ruminants, but also contribute with the greenhouse effect to the environment. Thus, mitigation strategies to reduce methane emissions from ruminants have been investigated. The aim of the present work was to evaluate the potential of tannins from 10 legume species (Flemingia macrophylla, Leucaena leucocephala, Stylosanthes guianensis, Gliricidia sepium, Cratylia argentea, Cajanus cajan, Desmodium ovalifolium, Macrotiloma axilare, Desmodium paniculatum and Lespedeza procumbens) as antimethanogenic strategies in beef cattle feeds on in vitro fermentation activity in the presence or absence of PEG (polyethylene glycol). Four adult rumen-cannulated Nellore cattle grazing a tropical grass pasture with free access to a mineral premix and fresh water were used as inoculum donors. A half gram of samples was incubated in serum bottles (160 mL) with 50 mL of buffer solution and 25 mL of inoculum at 39^oC for 24 h. For CH₄ determination, 2 mL of gas were sampled at each measuring time (3, 6, 9, 12, 18, 24 h) using a 5 ml syringe and stored in a 10 mL vacuum tube. The experimental layout included a randomized complete block with factorial design (12 forages with and without PEG) and four blocks (inoculum). The data were subjected to analysis of variance followed by Duncan test to determine the significance of the difference between treatment means. Values were considered significant at P < 0.05. Tannins from L. leucocephala, D. paniculatum and L. procumbens decreased methane production. PEG addition resulted in higher values isobutyrate, isovaleric, acetate and methane in these three species. The species L. leucocephala, D. paniculatum and L. procumbens have the potential to suppress rumen methanogenesis. However, in vitro fermentation of L. leucocephala resulted in greater degradability percentages.