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1197
Effect of introducing legumes containing condensed tannins in an orchardgrass diet on forage nutritive value and enteric methane output in continuous culture
Legumes containing condensed tannins (CT) have been shown to reduce enteric CH4 in ruminants; however, research is lacking on how increased CT levels affect forage nutritive value and CH4 output. A 4-unit, dual-flow continuous culture fermentor system was used to assess CH4 output of CT legumes in an orchardgrass diet (Dactylis glomerata). Treatments included: alfalfa (ALF, Medicago sativa) used as control, birdsfoot trefoil (BFT, Lotus corniculatus) as a low CT legume (7% CT, DM basis), crown vetch (CV, Coronilla varia) as an intermediate CT legume (12% CT, DM basis), and sericea lespedeza (SL, Lespedeza cuneata) as a high CT legume (31% CT, DM basis). Treatments were randomly assigned to fermentors in a 4 × 4 Latin square design using 7 d for adaptation and 3 d for collection. Feedings (82 g DM/d) occurred 4 times daily (07:30, 10:30, 14:00 and 19:00 h) throughout 4, 10-d periods. Treatments consisted of 50% orchardgrass and 50% legume. Forage samples were analyzed for DM, OM, CP, soluble and degradable protein, fiber, lignin, and NEL. Gas samples for CH4 analysis were collected 6 times daily (07:25, 09:00, 10:00, 13:55, 15:30, 16:30 h) during the last 3 d of each period and analyzed by GC (Varian CP 3800, Agilent Technologies, Santa Clara, CA). Methane data were analyzed using the GLIMMIX procedure of SAS (SAS Inc., Carey, NC) with treatment and period as fixed effects and fermentor as random effect. Pearson correlation coefficients between CH4 output and forage characteristics were determined using PROC CORR, and stepwise linear regression analysis was conducted according to PROC REG to detect predictive statistical associations between CH4 output and forage characteristics. Methane output of SL was 60, 68, and 73% less (P < 0.012) compared to CV, BFT and ALF, respectively. Crown vetch reduced (P < 0.025) CH4 output by 33% compared to ALF. There were no differences (P > 0.200) in CH4 output between BFT and ALF or BFT and CV. Correlation analysis revealed a positive relationship between CH4 output and degradable protein (r = 0.630, P = 0.009). An inverse relationship was found between CH4 output and OM (r = -0.520, P = 0.039). Stepwise regression analysis revealed that degradable protein explained 40% of the variation in CH4 output across all CT legumes. In summary, inclusion of legumes containing CT reduces CH4 output and was affected by nutrient content of the forage.
Keywords: condensed tannins, legumes, enteric methane