Production of Gas in Rumen Fermentations and Stable Mass Formation from Alfalfa Fiber and Pectic Substances

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Abstract
A series of laboratory experiments was carried out to identify the chemical characteristics of alfalfa considered a part of the complex causing stable foam formation in the rumens of cattle. Gas production in in vitro rumen fermentations, and stable foam formation after mechanically blending with water, were determined, using various fractions of alfalfa and other substances. The plant substances responsible for the initial rapid gas production obtained with green alfalfa were closely associated with the fiber fraction, but were removed after digesting in vitro 4-10 hours with rumen microorganisms or by extracting 12 hours with hot water. Purified pectin, crude pectins, glucose, and galactose increased gas production when added to washed alfalfa fiber. Hydrolyzed pectin produced the most marked effect, yielding 2.25 times as much gas as the washed fiber. Concurrent hydrolysis of macerated alfalfa with pectinase during digestion also increased gas production. Added pectin decreased the amount of plant material required to form a stable mass and increased the stable ingesta volume when incubated with rumen contents in vitro. The combined effects of the physical structure of green alfalfa fiber, pectic substances of alfalfa plants, galacturonic acid obtained on hydrolysis of pectic substances, and reducing sugars normally present are capable of causing the formation of stable foam found in pasture bloat.