Good Quality Grass Pasture Decreases Rumen Methane Production In Vitro.

Rumen methanogenesis and degradability characteristics of the most important foraging grasses for pastures in the tropics, i.e. Aruana (Panicum maximum), Napier grass (Pennisetum purpureum), Brachiaria (Brachiaria decumbens) and Buffel grass (Pennisetum ciliare), were evaluated in vitro using a semi-automatic system for gas production (GP). Samples of 0.25m2 (n = 2 for each cut) were collected from each production site, harvesting the plants with scissors at a height of 20 cm (the grazing portion of the stand). Grasses were collected throughout one year at different regrowth periods (2, 3 or 4 weeks) according to pasture availability. Higher (P<0.01) CP content was found for Aruana and Napier when compared with Brachiaria and Buffel, while Buffel showed the highest (P<0.01) NDF, ADF and cellulose compared with the other grasses. There were no differences (P=0.12) detected between grasses for GP, whereas Buffel had the highest (P<0.01) methane production levels (CH4) calculated either per unit of truly degraded organic matter (TDOM) (4.7, 5.6, 8.1 and 12.1; (SEM 2.59) ml/g TDOM) or degraded NDF (DNDF) (11.5, 20.3, 26.2 and 32.7 (SEM 11.1) ml/g DNDF), associated with the lowest (P<0.01) values of TDOM (0.23, 0.24, 0.21 and 0.15 (SEM 0.030) g/kg) and DNDF (189, 154, 135 and 111 (SEM 45.9) g/kg) respectively. The higher protein content for both Aruana and Napier was associated with the decrease (P<0.01) in CH4 production and with the increase (P<0.01) in the partitioning factor (PF) compared with other grass species. This suggests improvement of microbial growth efficiency by increasing the incorporation of rumen degraded organic matter into microbial cells, while the percentage partitioned into CH4 was decreased. It could be hypothesized that the better quality grass (characterized by lower fiber and higher protein content) is potentially promising to reduce the ruminal methanogenesis while improving organic matter degradability.