Development of a test diet for assessing the bioavailability of arginine in feather meal fed to rainbow trout (Oncorhynchus mykiss)

A 12-week slope ratio growth assay was undertaken to estimate the bioavailability of arginine in feather meal fed to rainbow trout. Fish were fed to satiety with isonitrogenous and isoenergetic diets containing graded levels of arginine provided by either synthetic l-arginine or steam-hydrolysed feather meal. Weight gain of the fish responded in a significantly linear (P < 0.0125) fashion to increase dietary levels of synthetic l-arginine. Weight gain of the fish did not significantly improve with increasing arginine level provided by feather meal. This result was unexpected since all diets were formulated to contain digestible essential amino acid (EAA) levels that were significantly in excess of NRC (1993) requirements. However, significant improvement in the feed efficiency, as well as nitrogen and energy utilization efficiencies, of fish fed the diets with increasing levels of feather meal, suggests that digestible nutrients from feather meal were, on average, very efficiently utilized by the fish.In a follow up experiment, supplementation of a high feather meal diet from the first experiment with a mixture of synthetic EAA significantly (P < 0.05) improved weight gain of the fish. These results indicate that the diets formulated to contain increasing levels of feather meal in the first experiment may have become deficient in one or more essential amino acids.This study highlights the need to have more accurate information on EAA requirements of fish for the development of slope ratio assays aimed at assessing the bioavailability of amino acids in different ingredients. It also shows the importance of generating more information on the bioavailability of individual EAA in feather meals.