In vitro methane production kinetics of red clover and grass silages used in dairy cow diets

Enhancing the proportion of red clover (Trifolium pratence) in grass swards offers multiple agronomic benefits like atmospheric nitrogen binding. We investigated fermentation kinetics and CH4 production of red clover silage in comparison to multispecies (50% Phleum pratense, 15% × Festulolium, 15% Lolium perenne, 10% Festuca arundinacea, 10% Festuca pratensis) grass silage using an automatic Gas Endeavour in vitro batch system. First cut wilted and formic acid-preserved silages were freeze-dried before incubation. The six experimental diets were as follows: pure grass silage (PG), pure red clover silage (PR), grass silage, barley, and oats (GC), red clover and grass silages, barley and oats (RGC), GC diet with faba bean (GCF), and RGC diet with faba bean (RGCF). In the diets with multiple feeds, red clover and grass silages were mixed 2:1, concentrates and silages 2:3, oat and barley 1:1, and oat, barley, and faba bean 3:3:4. Feeds were incubated for 22 h in an incubation medium of dairy cow rumen fluid and McDougall’s buffer solution (1:2). Total gas and CH4 productions were continuously measured. The experiment was repeated in 4 replicates and data analysed using SAS Mixed procedure. Both silages were of good quality, but red clover silage was less extensively fermented and had more crude protein (18.9% vs. 14.6%) and less NDF (34.0 vs. 51.2%) than grass silage. After incubation, diets including concentrates had lower pH and less residual dry matter than pure silage diets. Red clover and faba bean increased final pH of incubation media but did not affect dry matter disappearance. Total gas production was greater for PR than for PG, whereas it was smaller for RGC and RGCF than for GC and GCF. Diets with concentrates produced more gas than pure silages. Faba bean increased gas production only when red clover was not included (i.e. GCF vs. GC). Red clover did not affect CH4 production but inclusion of concentrates and faba bean increased CH4 production by 28% and 48%, respectively, compared to pure grass diets. Red clover fermented faster than grass silage. Cumulative total gas production was 62% greater for PR than for PG at 4 h but only 11% greater at 22 h. Similarly, red clover increased the rate of CH4 production by 110% although it did not increase CH4 total production. Overall, the differences in gas production were smaller between the mixed diets (RGC and RGCF vs. GC and GCF) than between the pure silages (PR vs. PG). Faster fermentation of red clover silage in comparison to grass silage was consistent with existing literature (e.g. Kuoppala et al., 2009). Our results suggest that despite differences in rate of CH4 production, the differences in total CH4 production between the red clover and grass silage diets seem minor.