Effect of extrusion on the rumen undegradable protein fraction of lupins

Abstract

Lupins are highly degradable in the rumen, and do not provide enough bypass protein for high-producing ruminant animals. The effects of extrusion on dry matter (DM) and crude protein (CP) rumen degradability of Lupinus albus and Lupinus angustifolius were determined in situ. Samples of both types of lupin were extruded at maximum temperature, which reached 116 °C. Six Dohne Merino wethers fitted with rumen cannulas were used in this trial. Samples were incubated in the rumen at intervals of 0, 2, 4, 12, 36, and 48 hours. This procedure was repeated in two sheep per treatment and in three periods, giving a total of six observations for each variable. Extrusion lowered the soluble fraction of CP and increased the potential degradable fraction without affecting its rate of degradation. It also lowered the effective degradability of CP of both types of lupin by 28% at an outflow rate of 0.08% per hour. No differences were observed between types. Extrusion modified the ruminal degradation parameters and decreased effective rumen degradation, especially at faster outflow rates. Thus, the rumen undegradable protein (RUP) fraction of lupins was increased by extrusion and lupins could be used more efficiently in ruminant diets. This study showed that the benefits of extrusion could be reached at a relatively low temperature of 116 °C to reduce the possibility of heat damage.