PSXI-21 Effect of the inclusion of increasing levels of three tree species on methane production and nutrient digestibility in vitro

Abstract Beef production is a major contributor to the world’s food system. However, it also represents a significant source of enteric methane (CH4). Currently, the incorporation of plants with increased concentrations of secondary metabolites has been highlighted as a strategy to mitigate enteric CH4. The objective of the present study was to evaluate the effect of increasing levels of three tropical trees in combination with a tropical pasture on total gas production, dry matter (DM) digestibility, neutral and acid detergent fiber (NDF and ADF, respectively) and volatile fatty acid concentration under in vitro conditions. Treatments were arranged in a completely randomized block design with 3 × 4 factorial arrangement, including three tree species [Gliricidia sepium (GS); Guazuma ulmifolia (GU) and Leucaena leucocephala (LL; Table 1)] × four increasing levels of inclusion (0, 15, 30 and 45%). Each experimental treatment was incubated in triplicate in three independent runs (blocks). All experimental units were incubated with 0.5 g of substrate (mixture of arborea with tropical grass) and gas production was measured at different times 0, 2, 4, 6, 8, 8, 10, 12, 14, 16, 20, 24, 30, 36, 48, 60 and 72 h of incubation. Ruminal fermentation was measured by the in vitro gas production technique, using a ruminal inoculum from three bovine donors. The data were analyzed with the MIXED procedure of SAS, and the comparison of means was analyzed with Tukey. The treatments that presented greater NDF digestibility were GS45 (53.79%) and GS15 (51.19%) while for ADF they were GS15 (35.15%) and GU15 (35.28%) and for DM it was GS30 with 71.32% (P < 0.05; Table 2). As for the volume of CH4 produced LL45 presented the least value (10.01%), following the same trend its NDF digestibility with 38.5% (P < 0.0001). While GU45 produced the lowest volume ml CH4 /g DM, NDF and ADF producing 25.83, 52.87 and 109.74 ml (P < 0.0001). Likewise, the tree species that had a reduced response in CH4 production were GU and LL compared with GS (P < 0.0001) also presenting a greater concentration of total and condensed tannins. The incorporation of forage plants with increased concentration of secondary metabolites and the reduced availability of digestible substrate in the present study reduced CH4 production in vitro. This study was partially funded by PAPIIT-DGAPA-UNAM (grant IN212523).