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Effect of Carbon-4 and Carbon-5 Volatile Patty Acids on Digestion of Plant Cell Wall In Vitro¹

Department of Animal Science and Agricultural Research Service, Cornell University and US Department of Agriculture, Ithaca, NY 14853

ABSTRACT

When mixed ruminal bacteria were incubated in an artificial medium with isolated plant cell walls, cell wall digestion and ammonia utilization were increased by low concentrations (< .30 mM) of carbon-4 and carbon-5 volatile fatty acids (isobutyric, isovaleric, valeric, and 2-methylbutyric). Carbon-4 and carbon-5 acid supplementation also increased cell wall digestion of intact forages. No pattern was observed between protein content of the feed and response to carbon-4 and carbon-5 volatile fatty acids.

Only the branch-chain acids (isovaleric, isobutyric, and 2-methylbutyric) stimulated bacterial growth and plant cell wall digestion. No synergisms were observed among the branched-chain acids, and they could replace each other. Valeric acid, a straight chain compound, was without effect, and phenylpropionic and phenylacetic acids likewise did not improve digestibility. The peptide source, Trypticase, enhanced cell wall digestion more than carbon-4 and carbon-5 volatile fatty acids alone, and this observation suggested that fiber digesting bacteria may be stimulated directly by amino acids or peptides.

¹ This work was taken from a thesis submitted by A.R.G. to Cornell University in partial satisfaction of requirements for a M.S. degree.

² Agricultural Research Service, US Department of Agriculture.

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