Effects of Diet Composition and Yeast Cell Wall Supplementation on Ruminal Fermentation, Gas Kinetics, Methane Production and Digestibility Assessed In Vitro Using Gas Production and Daisy(II) Incubator Systems.

内容摘要

Optimizing ruminant diets and mitigating methane emissions using feed additives like yeast cell wall is of growing significance in animal nutrition. The present study aimed to evaluate the effects of varying roughage-to-concentrate (R:C) ratios and yeast cell wall (YCW) supplementation on rumen fermentation, gas kinetics and methane (CH4) production using an in vitro modified Hohenheim gas production (GP) system. In addition, in vitro digestibility (true, organic matter and neutral detergent fibre digestibility) was assessed using the ANKOM DaisyII incubator. Both systems employed the same rumen inoculum. A 3 × 2 factorial design was used, involving three different R:C ratios with or without YCW supplementation. The diets were formulated as total mixed rations, comprising roughages (wheat straw, vetch hay in equal proportions) and a concentrate mix at ratios of 30R:70C, 50R:50C and 70R:30C. A YCW supplement containing ∼40% crude protein, a minimum of 18% of mannan-oligosaccharides and 18% of β-glucans was added at 1.25 g kg-1 diet. The results showed that cumulative (48 h) and asymptotic GP did not differ among diets with varying R:C ratios. The 30R:70C diet showed a significantly higher gas rate constant and longer lag time than the other diets. YCW supplementation significantly reduced total and asymptotic GP and increased lag time. Significant R:C × YCW interactions were observed for GP and gas rate constant, as well as for 24 h CH4 production. At 48 h, CH4 output was similar for the 30R:70C and 50R:50C diets, while 70R:30C diet exhibited significantly lower CH4 production than the 30R:70C diet. Increasing roughage proportion reduced digestibility, while pH, volatile fatty acid (VFA) profiles and ammonia nitrogen (NH3-N) concentrations remained comparable across diets. YCW supplementation had no significant effect on diet digestibility, pH or VFA profile, although it tended to reduce NH3-N levels. YCW supplementation also reduced CH4 production, with greater effects observed in high roughage diets. Overall, YCW supplementation reduced total gas and CH4 volumes and influenced gas kinetics differently based on the R:C ratio. Further research is recommended to investigate the effects of YCW under different diet compositions, inclusion levels and shorter incubation periods.