Nutritive value of raw and extruded pea-rapeseed blends for ruminants

An experiment was carried out to evaluate the nutritive value of raw and extruded pea-rapeseed blends. Whole pea and full-fat rapeseed were mixed in 60/40 and 80/20 proportions. Cooking lasted 30 min at 80 °C and extrusion was performed at 165 and 145 °C for 60/40 and 80/20, respectively. Extrusion decreased in situ degradation rate: 41, 70 and 77% respectively for crude protein, dry matter and neutral detergent fibre (NDF) for pea/rapeseed blends. When changes in solubility or potential degradability are included, extrusion decreased effective degradation in the rumen: 82, 96 and 93% for crude protein, dry matter and NDF, respectively. A large compensation in nitrogen digestion occurred in the intestine for extruded blends. The heat treatment increased the PDI values of the feeds and thus the delivery of amino acids to the intestine. Nevertheless, when expressed as a percentage of PDIE, the LysDI and MetDI values of blends are reduced with extrusion. An in vivo trial performed with dairy goats showed no digestive interaction between forage and these concentrates. Organic matter digestibility of concentrates was only slightly decreased by extrusion and the energy values of pea-rapeseed blends were largely a consequence of their fat content. Moreover, for the same level of fat intake, the extrusion process increased the proportion of C18:l, C18:2 and C18:3 in the milk fat. These results emphasise the interest of such feeds for dairy ruminants, even at a high level in the diet.