Enteric Methane Production and Ruminal Fermentation from Forage Brassica Diets Fed in Continuous Culture

Brassicas provide forage for livestock during the late fall when traditional perennial cool-season forages are not productive. However, little research exists on ruminal fermentation and CH₄ production of brassicas fed as forage. A continuous culture fermentor system was used to assess nutrient digestibility, VFA production and daily CH₄ production of brassicas. Treatments were randomly assigned to fermentors in a 4 × 4 Latin square design using 7 d for adaptation and 3 d for collection. Treatments were: 1) 50% orchardgrass (Dactylis glomerata L.) + 50% canola (Brassica napus L.; CAN); 2) 50% orchardgrass + 50% rapeseed (Brassica napus L.; RAP); 3) 50% orchardgrass + 50% turnip (Brassica rapa L.; TUR); and 4) 50% orchardgrass + 50% annual ryegrass (Lolium multiflorum Lam.; ARG). Feedings (82 g DM/d) occurred 4 times throughout four 10-d periods at 730, 1030, 1400, and 1900 h. Methane samples were collected every 10 min using a photoacoustic gas monitor (LumaSense Technologies, Inc.; Santa Clara, CA) during the last 3 d of the experiment. Effluent samples were collected on d 8, 9, and 10, composited by fermentor within period, and analyzed for VFA and pH as well as DM, OM, CP, and fiber fractions for determination of nutrient digestibility. Data were analyzed using the GLIMMIX procedure of SAS (SAS, Inc.; Cary, NC). Apparent DM, OM, and NDF digestibilities and true DM and OM digestibilities were not different (P > 0.28) among treatments (45.1, 63.2, 44.1, 67.1, and 87.2%, respectively). Total VFA (87.2 mol/100 mol), pH (6.47) and acetate (44.6 mol/100 mol) were also not different (P > 0.20) among treatments. Propionate was greater (P < 0.05) in ARG than CAN and RAP (25.8 vs. 22.0 mol/100 mol). Butyrate was greater (P < 0.04) in RAP than ARG (16.8 vs. 11.4 mol/100 mol). Daily CH₄ production was greater (P < 0.01) in ARG than all other treatments (68.9 vs. 11.2 mg/d). Methane, whether expressed as g per g of OM, NDF, digestible OM, or digestible NDF fed was greatest (P < 0.01) in ARG but similar (P > 0.18) among brassica treatments. Addition of brassicas provided similar nutrient digestibility to ARG while reducing daily CH₄ production, potentially making brassicas a more environmentally friendly alternative for ARG in pasture-based ruminant diets.