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

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-methylbutyric 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 rumn 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 digestibilities 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.