Effects of dietary cellulose level on pellet quality and nutrient digestibilities in rainbow trout (Oncorhynchus mykiss)

The study was conducted to examine if cellulose affected physical characteristics of extruded feed and nutrient digestibilities in rainbow trout. Five diets with cellulose inclusion levels ranging from 0 to 150 g kg− 1 were produced with a target apparent bulk density of 520 g l− 1 and fed to triplicate groups of fish (average weight 0.45 kg) twice a day for 31 days. Production parameters during feed production and physical pellet quality were recorded. During the feed production specific mechanical energy (SME) was around 32 watt hour (Wh) kg− 1 for all of the five extruded diets. Pellet expansion decreased linearly with cellulose inclusion, while pellet hardness and durability increased in a non-linear manner. There was a non-linear increase in water hydration capacity and a decrease in protein dispersibility index in response to increasing dietary cellulose level. No significant effects of cellulose inclusion were found on digestibility of main nutrients. The faecal excretion of sodium increased significantly with increased cellulose inclusion. In conclusion, digestion of main nutrients in rainbow trout was not affected by cellulose inclusion, but cellulose inclusion increased pellet durability and hardness.