EFFECT OF BRANCHED-CHAIN AMINO ACIDS OR FATTY ACID SUPPLEMENTATION ON IN VITRO DIGESTIBILITY OF BARLEY STRAW OR ALFALFA HAY

Abstract

In vitro dry matter digestibilities of ground barley straw or alfalfa hay, supplemented with branched-chain amino acids (valine, leucine and isoleucine) or their corresponding fatty acids (isobutyric, isovaleric and 2-methyl butyric acids), at 4% of substrate dry matter were determined. In vitro digestibilities were obtained after incubation in either rumen fluid or rumen fluid followed by pepsin in 0.1 N hydrochloric acid. Urea was added to the branched-chain fatty acid treatments so they were isonitrogenous with the amino acid treatments. Digestibility of barley straw was increased (P < 0.05) by supplementation with all branched-chain fatty acids, when added either alone or in combination in both digestion systems. The greatest increase was from 34.8% for unsupplemented barley straw to 63.1% for barley straw plus all three branched-chain fatty acids. Valine did not improve digestibility of barley straw when incubated with either rumen fluid or rumen fluid followed by pepsin solution. Addition of isoleucine increased digestibility (P < 0.05) of barley straw in both systems, while leucine was effective only when samples were incubated in both rumen fluid and pepsin solution. However, all combinations of amino acids increased (P < 0.05) the digestibility of barley straw in both systems. In vitro digestibility of alfalfa hay was increased (P < 0.05) only when valine and leucine were used together in either system. Incubating alfalfa hay in rumen fluid plus pepsin solution increased (P < 0.05) in vitro digestibilites for all treatments. The greatest increase was from 72.8% for control to 89.5% for the treatment receiving a combination of valine and leucine. Key words: In vitro dry matter digestibility, branched-chain amino acids, branched-chain fatty acids, barley straw, alfalfa hay