Degradation in the rumen and nutritional value of lupin (Lupinus albus L.) seed proteins effect of extrusion

The objective of the present study was to assess, by in vivo measurements, the nutritive value of raw and extruded lupin seed proteins. The contribution of both particle associated and soluble proteins to the duodenal flow of lupin crude protein (CP) was determined. Furthermore kinetics of lupin CP degradation in the rumen was determined. A group of six fistulated sheep was used in a duplicated 3×3 Latin square design experiment. A control diet (diet C), in which urea and starch substituted for lupins, was included to enable determination of rumen escape of lupin CP. In the other two diets, raw (diet RL) or extruded (diet EL) lupin seeds (Lupinus albus, cultivar ‘Arès’) were used as the protein supplement, and both were ground to pass a 3 mm screen. Lupins provided 20% of the dietary dry matter, 50% of dietary CP, in both diets RL and EL. The undegraded CP fraction of lupins estimated by in situ measurements (i.e. particle associated outflow) was 4 and 25% for raw and extruded lupins, respectively. Lupin soluble CP not degraded in the rumen was 4.5 and 1.8% of lupin CP for raw and extruded seeds, respectively. By adding particle associated and soluble fractions, rumen degradability of raw and extruded lupin seeds was 92 and 73%, respectively. These values are consistent with calculated lupin CP flow to the duodenum, 92 and 74%, for raw and extruded lupins, respectively. The increase in dietary non-ammonia N (NAN) flow to the duodenum with lupin extrusion was balanced by a decrease in microbial flow, and total NAN flow did not differ between diet RL and EL. Apparent NAN digestion (% of N intake) in the small intestine was not affected by extrusion. Although dietary NAN contribution to duodenal flow increased from 16 to 24% between diet RL and diet EL, the profile of apparently absorbed amino acids did not differ. The in situ technique underestimates the nutritive value of lupin seed CP mainly from not considering solubilised lupin CP that escape ruminal degradation. By increasing rumen CP escape and intestinal CP digestibility, extrusion improved the nutritive value of lupin seed CP.