Potential of mimosine of Leucaena leucocephala for modulating ruminal nutrient degradability and methanogenesis

Two in vitro assays were accomplished to assess whether low or high mimosine naturally found in leucaena (Leucaena leucocephala), contribute to methane (CH4) suppression. The first assay aimed to detect the effects of leucaena samples containing low or high mimosine levels on tannin bioactivity and ruminal CH4 production. Samples containing 43.9 ± 1.9 g condensed tannin (CT)/kg DM were divided into two groups based on their mimosine contents (n = 4/group): low (2.3 ± 0.1) and high (11.1 ± 1.5) g mimosine/kg DM. Leucaena incubations were made with or without polyethylene glycol (PEG). In the second assay, two leucaena samples similar in CT content and chemical composition were selected from the first assay to examine the effect of level of mimosine naturally found in leucaena, as well as the direct effect of mimosine when added to Tifton (Tifton 85; Cynodon dactylon (L.) and lucerne (Medicago sativa L.) hays on ruminal fermentation and nutrient degradation. The results of the first assay showed that leucaena containing low mimosine with or without PEG decreased (P < 0.01) gas production (GP), but presented higher values of the percent increase in gas (P = 0.03) and CH4 (P < 0.01) production after PEG addition compared to leucaena containing high mimosine. The addition of PEG in the second in vitro assay enhanced GP (P = 0.007) and CH4 (P < 0.05) by both types of leucaena, while decreased (P = 0.01) propionate, and increased (P = 0.003) C2/C3 and NH3N (P = 0.02) concentrations by leucaena containing low mimosine compared with PEG non-supplemented leucaena. However, such an effect did not occur by leucaena containing high mimosine. L-mimosine recorded 27% (P = 0.02) and 10% (P = 0.08) CH4 reduction when supplemented at a high level with Tifton and lucerne, respectively, while enhanced (P < 0.05) the true degradability of organic matter (TDOM), acetate and NH3N, compared with zero mimosine supplementation. Forages without any supplementation also affected the ruminal fermentation; similar reduction (P < 0.05) of CH4 production was found for both leucaena samples compared to Tifton and lucerne. Leucaena containing high mimosine enhanced TDOM (P < 0.01), acetate (P = 0.01) and NH3N (P = 0.05). These results indicated that leucaena containing high mimosine modulated ruminal fermentation in a different way than did the leucaena containing low mimosine.