Relationship between predicted in vivo and observed in vivo methane production from dairy cows fed a grass-silage based diet with barley, oats, or dehulled oats as a concentrate supplement

Abstract

The objectives of this study were to compare predicted in vivo methane (CH4) values based on data from an in vitro gas production experiment with observed in vivo values measured by the GreenFeed system, and to investigate the effect of the diet fed to donor animals of rumen inoculum (RI) on predicted in vivo CH4 production. For this purpose, we conducted an in vivo experiment simultaneously with an in vitro gas production experiment. The in vivo experiment (previously published) was a 4 × 4 Latin square design including 16 Nordic Red dairy cows. Cows were fed 60% grass silage and 40% concentrate which consisted of either barley, oats with hulls (hulled oats), dehulled oats, or a 50:50 mixture of hulled and dehulled oats on dry matter basis. The in vitro experiment was a 2 × 4 factorial design replicated in 4 runs. The in vitro diets were incubated for 48 h in two types of RI and formulated according to the diets fed in vivo. The RI was obtained from cows fed either barley (two cows) or hulled oats (two cows) as concentrate in the in vivo experiment. A set of models were applied to the gas and CH4 data obtained from the in vitro system to predict in vivo total gas and CH4 production. For the comparison between predicted in vivo and observed in vivo CH4, two different mean retention times (MRT of 35 and 50 h) in the rumen were used for the predictions. In the in vitro experiment, incubation residues were determined for organic matter digestibility and volatile fatty acids at 48 h of incubation. Assuming a MRT of 35 h in the rumen resulted in a significant relationship (P = 0.04) between predicted in vivo and observed in vivo CH4 yield (g/kg dry matter) with an R-square of 0.91 and a root mean square error of 0.20. Ranking of the diets in terms of their CH4 production was consistent between the in vitro and in vivo experiment. There were no significant interactions between diet and RI for any of the investigated parameters (P = 0.40). Rumen inoculum did not affect organic matter digestibility or total volatile fatty acid production. In conclusion, there was a good agreement between predicted in vivo and observed in vivo CH4 values. In addition, the diet of RI donor animal did not influence the comparison of diets in terms of CH4 production.