Effect of extrusion on ruminal and intestinal disappearance of amino acids in white lupin seed

Abstract

The effect of extruding white lupin seed (WLS) at 120 or 150 °C on the degradability of crude protein in the rumen and the intestine of nonlactating Holstein cows was determined in situ. Nylon bags were incubated in the rumen for 16 h and then introduced into the small intestine, through a duodenal cannula, for subsequent recovery in feces. Extrusion of WLS at 120 or 150 °C decreased the degradability of crude protein in the rumen (86.9–73.6 vs. 98.4%) and increased the amount of crude protein disappearing in the intestine (11.8–25.0 vs. 0.8%). Extrusion did not alter the amino acid (AA) profile of WLS, although the AA composition of the WLS protein that escaped ruminal digestion differed markedly both quantitatively and qualitatively, from its initial composition. Extruding WLS increased intestinal disappearance of most of the AA, but variation in disappearance among AA was substantial. Thus, WLS proteins that are not degraded in the rumen differ in their potential as a source of absorbable AA in the intestine from the original source. Comparison of essential AA profiles of original sources to that of milk indicated that the sulphur AA were first-limiting in WLS, with valine, lysine and leucine being second through fourth limiting. The estimated AA chemical score (test-to-milk ratio) for original WLS was 64%. For the rumen undegraded protein fractions disappearing in the intestine, the limiting AAs in descending order were: sulphur AA, valine, phenylalanine plus tyrosine and threonine for raw WLS; sulphur AA, lysine, valine and histidine for WLS extruded at 120 °C and lysine, valine, histidine and sulphur AA for WLS treated at 150 °C. The corresponding AA chemical scores were: 63, 76 and 72%. Consequently, after extrusion, the ruminally undegraded protein of WLS that disappeared in the intestine showed a higher protein quality. Key words: Cow, lupin, seed, amino acids, extrusion, ruminal degradation, intestinal disappearance