Influence of Accompanying Substrate on In Vitro Volatile Fatty Acid Formation from α-Cellulose-14C1,2

Abstract

The effect of accompanying substrate on volatile fatty acid (VFA) formation from α-cellulose-14C incubated 4 hr with ruminal ingesta obtained from a cow fed either alfalfa hay (H) or a 2.5:1 grain–alfalfa hay mixture (G) was investigated. Addition of starch or linoleic acid to H or G ingesta had no discernible effect on the relative amounts of titratable VFA or VFA-14C produced. Continuous flushing of the incubating H or G ruminal ingesta with N2 or CO2 had no significant effect on the production of titratable VFA or VFA-14C, but did affect the route of propionate formation. Continuous gassing with CO2 increased the proportion of propionate formed by the randomizing route.Addition of sodium lactate markedly increased the molar percentage of titratable butyrate and butyrate-14C. The dramatic change in titratable VFA and VFA-14C production caused by the addition of sodium lactate was considered evidence for the direct influence ration constituents or feed additives could have on the rumen fermentation by altering the metabolic routes used by the existing microbial population.The randomizing route of propionate formation accounted for 82% or more of the propionate formed when H ingesta was subjected to the various treatments. With the G ingesta, 63% or more of the propionate was formed by the randomizing route.