Potential of Soybean Meal as a Protein Source in Extruded Pellets for Rainbow Trout.

Abstract

The potential of defatted soybean meal (SBM) as a protein source in high energy diets (extruded soft-dry pellets, SDP) was studied with rainbow trout of about 5g. The SDP contained respectively 0, 20, 30, 40, and 50% SBM, or 25% SBM plus 15% corn gluten meal (CGM) as a substitute for fish meal. The digestibility of SBM nutrients in SDP was determined using a reference diet and test diets which were formulated to contain both the reference diet and SBM in a ratio of 70:30, 60:40, and 50:50, respectively.The combination of 25% SBM with 15% CGM produced the best growth, while inclusion of SBM up to 50% did not reduce growth or protein utilization efficiency compared to the control diet. However, feed efficiency was slightly lower in SBM supplemental diets caused by the undigestible carbohydrate portion of SBM. The digestibility of protein, starch, and energy of SBM was 91, 54, and 80%, respectively, rather unaffected by the SBM levels in the formulation.It was concluded that SBM can be included up to 50% in SDP, replacing up to 91% of fish meal, supporting excellent growth and feed performance. A combination of 25% SBM and 15% CGM was confirmed to be an effective alternative protein source for rainbow trout.