Comparing Rumen Fluid to Buffer Ratios to Estimate in vitro Degradability, Fermentation, and Methane Profiles of Seven Forages at Two Incubation Times

Using different rumen fluid (RF) or RF to buffer (B) ratios (RFB) could be a limiting factor in evaluating numerous feeds for obtaining reproducible estimates of in vitro rumen degradability. Thus, two duplicated factorial experiments (exp) compared the effect of changing the RFB ratios on degradability, fermentation, and methane profiles of seven forages during in vitro incubations with 40 mL of buffered RF (inoculum, RI) for 48 and 96 hours. Exp 1 (7×2×2) involved 7 forages (F) and 2 RFB ratios (1:2 and 1:4), for two in-cubation times (T, 48 and 96 hours). The main effects of F and T were significant (P<0.05) but the effect of RFB ratio was not always significant (P>0.05) for the mean in vitro dry matter degradability (IVD) and organic matter degradability (IVOMD). The mean IVD and IVOMD of each forage and mean of all forages were significantly (P<0.05) higher after 96 h than 48 h of incubation. The F × RFB interaction was signifi-cant (P<0.05) for IVD and IVOMD depending on different RFB ratios. In exp 2 (7×2) involving the same 7 forages and 2 RFB ratios, total gas volume and methane were significantly (P<0.001) higher for the 1:2 than the 1:4 RFB ratio. Methane concentration was higher for the high fibrous than the low fibrous forages. Ammonia concentration, total gas volume, and methane production correlated positively with IVD. It ap-peared that the degradability, fermentation, and methane profiles of different forages were influenced by the RFB ratios, and in vitro incubation times. However, the changes in IVD and fermentation profiles were not proportionate to the change in RFB from 1:4 to 1:2. IVD for 1:2 and 1:4 ratios are very highly correlated at both 48 and 96 h. Thus, the use of diluted rumen fluid with a 1:4 RFB ratio is proposed suitable for subse-quent studies to rank a wide range of feed ingredients for both degradability and methane measurements. However, in places where it is easy to collect RF can continue in vitro trial with a 1:2 RFB ratio.