Effects of Starch Content on Hydrogen and Methane Productions, Rumen Fermentation and Microbial Protein Synthesis During in Vitro Ruminal Culture

Background: Starch has faster rate of rumen fermentation than fiber, and always causes a rapid increase in ruminal molecular hydrogen (H 2 ) partial pressure and microbial protein synthesis, which may promote other H 2 sinks to compete H 2 from methanogenesis. The study was designed to investigate the effects of increasing starch content on methane (CH 4 ), hydrogen gas (gH 2 ) production, rumen fermentation, metabolic hydrogen ([H]) production, microbial protein (MCP) synthesis through in vitro ruminal batch incubation. Methods: : Seven different treatments was prepared by replacing corn straw with corn grain, and starch content were 72, 185, 297, 410, 525, 634 and 747 g/kg DM. Results: : Elevating starch content increased DM degradation ( P linear < 0.001), and decreased the CH 4 ( P linear and P quadratic < 0.001) and gH 2 ( P linear < 0.001) productions relative to DM degraded. Elevating starch content increased VFA concentration ( P linear < 0.001), propionate molar percentage ( P linear < 0.001; P quadratic = 0.001) and MCP concentration ( P linear and P quadratic < 0.001), and decreased acetate molar percentage ( P linear < 0.001), acetate to propionate ratio ( P linear < 0.001) and estimated net [H] production relative to DM degraded ( P linear < 0.001). Elevating starch content decreased molar percentage of [H] utilized for CH 4 ( P quadratic = 0.003) and gH 2 ( P linear < 0.001) production. Conclusion: Increasing starch content alters rumen fermentation pathway from acetate to propionate production with reduction in efficiency of [H] production, promotes H 2 utilization with enhanced MCP synthesis and leads to the reduction in efficiency of CH 4 and gH 2 production.