Effects of supplementation of Simmental steers with 2-methylbutyrate on rumen microflora, enzyme activities and methane production.

The objective of this study was to evaluate the effects of 2-methylbutyrate supplementation on rumen microflora, enzyme activities and methane production in Simmental steers consuming a diet consisting of 600 g/kg corn stover and 400 g/kg concentrate (dry matter [DM] basis). Eight ruminally cannulated Simmental steers were used in a replicated 4 × 4 Latin square design. The treatments were: control (without 2-methylbutyrate), low 2-methylbutyrate (LMB), medium 2-methylbutyrate (MMB) and high 2-methylbutyrate (HMB) with 0, 8.4, 16.8 and 25.2 g 2-methylbutyrate per steer and per day, respectively. Dry matter intake (averaged 9 kg/day) was restricted to a maximum of 0.9 of ad libitum intake. Whether direct counts, roll-tube technique or real-time PCR quantification were used, populations of total bacteria, cellulolytic bacteria and anaerobic fungi linearly increased (P<0.04) and were higher (P<0.05) for MMB and HMB than for control and LMB, whereas those of protozoa and total methanogens linearly reduced and were lower for MMB and HMB than for control and LMB. With increasing 2-methylbutyrate supplementation, real-time PCR quantification of populations of Ruminococcus albus, Ruminococcus flavefaciens, Bufyrivibrio fibrisolvens and Fibrobacter succinogenes linearly increased (P<0.05) and was higher for MMB and HMB than for control (P<0.05). Activities of CMCase, xylanase and β-glucosidase linearly increased (P<0.05) and were higher (P<0.05) for MMB and HMB than for control and LMB, whereas that of protease linearly reduced (P<0.05) and was lower for MMB and HMB than for control and LMB (P<0.05). Activities of α-amylase and α-glucosidase tended to be higher (P<0.08) for MMB and HMB than for control and LMB, but activity of urease tended to be lower for MMB and HMB than for control and LMB. Methane production linearly decreased (P<0.01) and was lower for MMB and HMB than for control (P<0.05) with increasing 2-methylbutyrate supplementation. Effective degradabilities of cellulose and hemicellulose of corn stover linearly increased (P<0.01) and were higher for MMB and HMB than for control (P<0.05), whereas that of crude protein in concentrate linearly decreased (P<0.01) and was lower for MMB and HMB than for control and LMB (P<0.05) with increasing 2-methylbutyrate supplementation. The present results indicate that supplementation of diet with 2-methylbutyrate altered ruminal microbial populations and improved ruminal enzyme activities in a dose-dependent manner in steers fed high-roughage diet. In the experimental conditions of this trial, the optimum daily dose of 2-methylbutyrate at 16.8 g per steer is suggested.