The potential benefit of corn dried distillers' grain (co)products (DDG) in the mitigation of methane production in cattle: An in vitro analysis

Abstract Text: The objective of this work was to determine the impact of different levels of DDG on the digestibility of OM and the production of methane (CH₄) using an in vitro technique. Nine diets were formulated with Bermuda grass hay, ground corn, and alfalfa hay mixed with DDG (0, 10, 20, 30, 40, 50, 60, 80, and 100% of diet DM). These nine diets and alfalfa hay alone (laboratory control) were ground (1 mm), and incubated with rumen fluid (from grazing cows) and media. Blanks (rumen fluid and media only) were used to adjust the CH₄ production. Three replicates and 4 incubation times (3, 6, 24, and 48 h) were investigated in the bottle’s headspace using a syringe for collection. Because these diets had different amounts of potentially fermentable substrate, adjusted CH₄ was computed as CH₄ concentration divided by the amounts of NDF (CH₄NDF, mM/g NDF), NFC (CH₄NFC, mM/g NFC), fermentable carbohydrate (FCHO = CHOA + CHOB1 + CHOB2) (CH₄FCHO, mM/g FCHO), OM (OM = 100 – Ash) (CH₄OM, mM/g OM), and fermentable OM (FOM = OM – Ash – EE) (CH₄FOM, mM/g FOM) in the diet sample. The PROC MIXED of SAS (SAS Inst., Cary, NC) was used to analyze the data assuming a repeated measure design. Diets and incubation times were assumed as fixed factors and replicate within diet as random factor. Except for CH₄FCHO and CH₄NFC, diet effect was significant (P<0.001) for all other adjusted CH₄ concentrations, suggesting that FCHO and NFC may not explain differences in CH₄ concentration. Regarding incubation time and its interaction with diet, all adjusted CH₄ concentration were highly significant (P<0.001).There was a tendency to decrease CH₄ concentration as the DDG level increased, but the level of DDG in the diet had to be greater than 50% to yield significant reduction in the adjusted CH₄ concentration, CH₄FOM and CH₄OM (CH₄ per unit of OM) when the fat content was greater than 7.39% DM. Significant linear regressions for adjusted CH₄ concentration (CH₄ = 14.5 − 0.667 × Fat; r² = 0.64, RMSE = 1.48 mM, n = 46) and CH₄FOM (CH₄FOM = 83.8 − 3.35 × Fat; r² = 0.53, RMSE = 9.30 mM/% FOM, n = 46) on fat content of the diets were observed. These in vitro results suggested that under normal ruminal fermentation CH₄concentration will decrease as dietary fat increases if ruminal retention time is between 24 and 48 h.

Keywords: abatement, greenhouse gas, ruminant