269 Effect of oilseed source on ruminal fermentation and methane production of a grass-legume diet in continuous culture

Abstract

Addition of oilseeds to pasture-based ruminant diets has been shown to decrease enteric CH4 emissions. However, little research has directly compared the effect of oilseed source on ruminal fermentation and CH4 production. A 4-unit continuous culture fermentor system was used to test 4 oilseeds supplemented to a 45% orchardgrass (Dactylis glomerata L.) + 45% sericea lespedeza (Lespedeza cuneata Don. cv. Auburn Grazer) diet. Oilseeds (supplemented at 10% of total DM fed) were soybean (SOY), sunflower (SUN), canola (CAN), and a mixture of equal proportions of SOY, SUN, and CAN (MIX). Diets were randomly assigned to fermentors in a 4 × 4 Latin square design. Feeding occurred 4 times daily throughout four 10-d periods using 7 d for adaptation and 3 d for collection. Effluent samples were analyzed for pH, VFA, and DM, OM, ADF, and NDF digestibilities. Gas samples were recorded using a photoacoustic gas analyzer for total daily CH4 production. Data were analyzed using the GLIMMIX procedure of SAS with treatment as a fixed effect and fermentor and period as random effects. No differences (P > 0.10) were found for pH (7.10) among oilseeds. Total VFA concentration was greatest (P < 0.01) in SOY (46.0 mmol/L), with no differences (P > 0.05) among other oilseeds (38.2 mmol/L). There were no differences (P > 0.05) among oilseeds in molar proportions of acetate, propionate, isobutyrate, butyrate, isovalerate, and valerate. No differences (P > 0.10) were found for apparent and true DM and OM digestibilities or apparent ADF and NDF digestibilities. Total daily CH4 production and total CH4 production per gram of nutrients fed or per gram of digestible nutrients fed were greatest (P < 0.001) in SOY. The SOY produced daily 68, 81, and 85% greater (P < 0.001) amounts of CH4 (80.1 mg/d) compared to SUN, CAN, and MIX, respectively. No differences (P > 0.05) were found between SUN, CAN, and MIX for total daily CH4 production or total CH4 production per gram of DM, OM, ADF, and NDF fed or per gram of digestible OM fed. The SOY produced greater (P < 0.001) amounts of CH4 per gram of digestible DM fed or per gram of digestible ADF and NDF fed than MIX, with SUN and CAN showing intermediate levels. Addition of oilseeds such as SUN and CAN to a grass-legume diet is a potentially environmentally friendly feeding strategy to reduce enteric CH4 emissions without negatively impacting ruminal fermentation.