Apparent total tract digestibility of unprocessed and extruded diets containing basic and autolyzed bacterial protein meal grown on natural gas in mink and rainbow trout

A study was conducted to compare coefficient of total tract apparent digestibility (CTTAD) of diets where high-quality (LT) fish meal (FM) were partly replaced with basic bacterial protein meal (BPM) and autolyzed bacterial protein meal (BPA) in a carnivorous mammal (mink) and fish (rainbow trout). In mink, both unprocessed meal and extruded diets were tested, while only extruded diets were tested in rainbow trout. Adding BPM (0, 125 and 250 g kg−1) to diets had no effect on CTTAD of macronutrients in the unprocessed diets, but decreased the CTTAD of starch (linear P<0.001) in the processed diets. Adding BPA (0, 125 and 250 g kg−1) to both unprocessed and processed diets increased (linear P<0.05) the CTTAD of ash but reduced (linear P<0.001) the CTTAD of starch. In general, increasing levels of BPM in the diets had no adverse effect or slightly reduced the CTTAD of individual amino acids, while increasing levels of BPA had no adverse effect or increased the CTTAD of nitrogen and individual amino acids in both the unprocessed and the processed diets. Both bacterial protein meal products reacted similarly to extrusion with respect to CTTAD of macronutrients and individual amino acids. Extrusion improved the CTTAD of nitrogen, phenylalanine, and arginine, but decreased the CTTAD of tryptophan. In rainbow trout, diets containing BPA had lower CTTAD of starch than the control and the BPM diets. Increasing levels of BPM and BPA in the diets reduced the CTTAD of nitrogen, total amino acids, and several indispensable and dispensable amino acids. The CTTAD of nitrogen and indispensable amino acids were similar in BPA and BPM in rainbow trout. There were significant correlations between mink and trout for CTTAD of indispensable amino acids, ranging from 0.86 to 0.94, but the trout had higher CTTAD of nitrogen and amino acids than mink for all diets. The results suggest that both BPM and BPA could replace up to 250 g kg−1 of crude protein from high-quality fish meal in diets for mink and rainbow trout with only minor effect on CTTAD of amino acids and other nutrients.