Enteric methane production and ruminal fermentation of forage brassica diets fed in continuous culture

Authors: DILLARD, LEANNE - Auburn University; ROCA-FERNANDEZ, ANA - Universidad De Chile; RUBANO, MELISSA - Consultant; Elkin, Kyle; Soder, Kathy

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2018
Publication Date: 2/17/2018
Citation: Dillard, L., Roca-Fernandez, A., Rubano, M., Elkin, K.R., Soder, K.J. 2018. Enteric methane production and ruminal fermentation of forage brassica diets fed in continuous culture. Journal of Animal Science. 96:1362-1374. https://doi.org/10.1093/jas/sky030.
DOI: https://doi.org/10.1093/jas/sky030

Interpretive Summary: Forage brassicas are cool-season annual forages that can be used to fill 'forage gaps' when other pastures are not as productive, such as mid-summer and late fall. We added three forage brassicas (canola, rapeseed, and turnip) or one annual grass (annual ryegrass) to a perennial cool-season pasture (orchardgrass) to evaluate the effects of these forages on ruminal fermentation and methane production in a continuous culture fermentor system. Use of brassicas in a ruminant grazing system could extend the fall grazing season and reduce winter feed costs while increasing animal efficiency and decreasing enteric greenhouse gas emissions. Additional research is needed with grazing animals to evaluate the long-term effects of grazing brassicas on animal health, production efficiency, and greenhouse gas output.

Technical Abstract: The aim of the current study was to determine nutrient digestibility, VFA production, N metabolism, and CH4 production of canola (Brassica napus L.), rapeseed (B. napus L.), turnip (B. rapa L.), and annual ryegrass (Lolium multiflorum Lam.) fed with orchardgrass (Dactylis glomerata L.) in continuous culture. Diets were randomly assigned to fermentors in a 4 × 4 Latin square design using 7 d for adaptation and 3 d for collection. Diets were: 1) 50% orchardgrass + 50% canola (CAN); 2) 50% orchardgrass + 50% rapeseed (RAP); 3) 50% orchardgrass + 50% turnip (TUR); and 4) 50% orchardgrass + 50% annual ryegrass (ARG). Feedings (82 g DM/d) occurred 4 times daily throughout 4, 10-d periods at 730, 1030, 1400, and 1900 h. Methane samples were collected every 10 min using a photoacoustic gas analyzer (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, and analyzed for VFA and pH as well as DM, OM, CP, and fiber fractions for determination of nutrient digestibility. Forage samples were analyzed for CP, NDF, ADF, minerals, and glucosinolate (GLS) concentrations. Data were analyzed using the GLIMMIX procedure of SAS. Apparent DM, OM, and NDF digestibilities and true DM and OM digestibilities were similar (P > 0.28) among diets (45.1, 63.2, 44.1, 67.1, and 87.2%, respectively). Total VFA (87.2 mol/100 mol), pH (6.47) and acetate (A: 44.6 mol/100 mol) were also not different (P > 0.20) among diets. The A:P (P = propionate) ratio was greater (P < 0.01) in ARG and CAN than RAP and TUR. Daily CH4 production was greater (P < 0.01) in ARG than all other diets (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 diets. A significant negative correlation was observed between total GLS and CH4 production. However, when multiple regression analysis on CH4 production was completed, neither total GLS nor individual GLS were a significant component of the model. 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.