Sodium diformate and extrusion temperature affect nutrient digestibility and physical quality of diets with fish meal and barley protein concentrate for rainbow trout (Oncorhynchus mykiss)

The objective of the experiment was to evaluate the effects of ingredient, extrusion temperature, and the conjugated acid salt sodium diformate (HCOOH··HCOO-Na; NaDF) on apparent nutrient digestibility and physical quality of diets for rainbow trout. The experiment had a 23 factorial design with two dietary ingredient sources (fish meal [FM] and barley protein concentrate [BPC]), two extruder temperatures (110 and 141 °C), and two levels of NaDF supplementation (0 and 10.6 g kg− 1). The results from the digestibility trial showed that inclusion of BPC significantly increased the digestibility of crude protein and several non-essential amino acids (NEAAs), but significantly reduced the digestibility of crude lipid, starch, and all essential amino acids (EAAs). Extrusion at 141 °C significantly increased the digestibility of starch, crude protein, arginine, and several NEAAs, but significantly reduced the digestibility of phenylalanine compared to extrusion at 110 °C. Addition of NaDF significantly increased the digestibility of most major nutrients and individual amino acids. Diets with BPC had significantly higher hardness, expansion ratio, and durability, but significantly lower water stability compared to diets based on FM. Extrusion temperature only affected pellet durability, which was significantly higher for the highest temperature. Addition of NaDF to diets significantly increased the expansion ratio, durability, and water stability compared to diets without NaDF. This experiment showed that BPC is a promising alternative protein source to FM with regard to nutrient digestibility and physical quality of extruded diets. The use of high extrusion temperature (141 °C) and inclusion of NaDF improved both nutrient digestibility and physical quality of diets for rainbow trout.