Influence of extrusion on ruminal and intestinal disappearance of amino acids in whole horsebean

Abstract

Horse-beans (HB) were extruded at 120 °C. Two nonlactating Holstein cows with rumen and proximal duodenal fistulae were used to determine the effect of extrusion on in situ rumen degradation after 4, 8 and 16 h of incubation and intestinal digestibility of HB protein. Results of the present study indicate that processing diminished the ruminal degradability of HB proteins; after 4, 8 and 16 h of rumen exposure the nitrogen loss was reduced by 29, 31 and 18% respectively, with a corresponding increase in the amounts disappearing from the intestine of 110, 169 and 135%. Heat-treatment did not alter the amino acids (AA) profile; AA composition of the HB protein fractions that bypass the rumen may markedly differ quantitatively and qualitatively from their original composition. Extruding the beans increased intestinal disappearance of most of the AA, but variation in disappearance among AA was substantial. These results indicate that rumen undegraded proteins differ in their potential as a source for absorbable AA in the intestine. Comparison of essential AA profiles of original sources to that of milk indicated that the sulphur AA were first limiting in HB, with phenylalanine plus tyrosine and valine being second and third limiting. The estimated AA chemical score (test-to-milk ratio) for original HB was 61%. For the rumen undegraded protein fractions disappearing in the intestine, the limiting AAs in descending order were: sulphur AA, lysine, phenylalanine plus tyrosine and valine for raw HB; lysine, valine, phenylalanine plus tyrosine and sulphur AA for extruded HB. The corresponding chemical scores were 51 and 80%. Thus processing ameliorated the protein quality of the rumen undegraded fraction. Key words: Horsebean, amino acids, extrusion, ruminal degradation, intestinal disparition, cows