Influence of extrusion on ruminal and intestinal disappearance in sacco of pea ( Pisum sativum) proteins and starch

Abstract

Two Holstein steers fitted with permanent ruminal cannulae and three Belgian Blue bulls equipped with permanent ruminal and duodenal cannulae were used in two experiments to study ruminal protein and intestinal digestibility in sacco of extruded peas ( Pisum sativum). Samples of crude peas (5 g) and peas extruded at 140, 180 and 220 °C were weighed in large nylon bags and incubated in the rumen for 2, 4, 8, 16 and 24 h. Samples of peas (1 g) extruded at 140 °C, soya-bean meal and extruded soya-bean seeds were weighed in small bags, incubated in the rumen for 16 h and then inserted into the duodenum. Results were interpreted by fitting disappearance data of dry matter and nitrogen in the rumen by an iterative least squares procedure while intestinal disappearance was calculated from the amounts of initial and residual nitrogen in the bags at the duodenal and faecal sites. Extrusion of peas did not significantly affect dry matter effective degradability, but dramatically reduced crude protein effective degradability (88.3% vs. 65.5% at an outflow rate of 0.06 h −1). In addition, extrusion greatly increased the rate of disappearance of starch in the rumen. The small mechanically released crude protein fractions of the feeds did not lead to an important overestimation of their degradability nor did it affect their classification, but reflected the high protein solubility of the crude peas. In our experimental conditions, it appeared unnecessary to increase extrusion temperature above 140 °C. Above this temperature, protein protection was not significantly improved. The low values observed for residual nitrogen of mobile nylon bags (0.45 g kg −1 DM) and high nitrogen pepsin solubility (95.8%) of peas extruded at 140 °C demonstrate that extrusion had little or even no negative effect on intestinal digestibility. Extrusion failed to improve significantly the essential amino acids profile of extruded peas in the undegradable ruminal fraction but seemed to increase the essential amino acids concentration of residual extruded soya-bean seeds.