Graph Interpretations

X‐axis is time in hours.

Y‐axis is ml of gas produced from the 400 mg sample.

Total represents the curve of the total amount of gas produced from a 400mg sample incubated in rumen fluid for 48 hours. In general, 60% of the total gas production asymptote is reached in the first 24‐hours so this is the most important portion of the gas production curves to focus attention.

Slow represents the amount of gas produced from the slow pool. Given the heterogeneity of its nature, the slow pool is comprised primarily of fiber (B3 Pool, hemicelluloses and cellulose) along with slowly degradable starch.

Fast represents the gas produced from fast pool consisting primarily of B1 (starch) and B2 (soluble fiber) pools; although it is possible for very rapidly digesting (B3) fiber to also contribute to the fast pool of gas. In TMR’s, fast pool gas amounts higher than about 40 ml of gas are indicative of excess acetate (which produces gas) and reduced levels of propionate (minimal gas production and more ATP) coming from the fast pool nutrients. TMR samples with over 40ml of gas from the fast pool generally appear to need more energy for microbial protein production, thus supplementation should be considered using propionate producing feeds (grains) as opposed to forages or non‐forage fiber sources (NFFS) like soy hulls or beet pulp. It should be noted that these pools are not homogeneous because there can be both slow and fast pools within each carbohydrate fraction (e.g. the slow pool may contain some slowly digested starch). This fact may present challenges for those looking for an analysis that reflects the fermentation of chemically identifiable and measurable feed fractions, however, it does approximate the nature of ruminal fermentation and provides a practical means to evaluate rations, predict the productive response and make sound nutrition decisions affecting productivity and profitability (Johnston and Tricarico, 2007).