Growth and protein utilization in Atlantic salmon (Salmo salar L.) given a protease inhibitor in the diet

In a series of experiments the effects of dietary protease inhibitor inclusions on growth and amino acid absorption rate were investigated in Atlantic salmon (Salmo salar L.). An optimal inclusion of inhibitor was found by conducting dose-response studies with specific growth rate as the main response variable. No negative effects on feed conversion ratio or nitrogen digestibility were observed at this level. In protein sources studies the addition of potato protease inhibitor to a fishmeal based diet increased specific growth rate by 14%. When a proportion of the fishmeal was replaced with hydrolysed protein (fish silage) the addition of the inhibitor resulted in a 31% increase in specific growth rate. Absorption of amino acids from the gastrointestinal tract into the blood was investigated in two experiments using C-14-labelled algal (Synechoccus leopoliensis) protein. The absorption pattern of C-14-labelled amino acids was altered by adding potato protease inhibitor when the algal protein was supplied in intact form, but not when the algal protein was hydrolysed. The absorption of amino acids from a hydrolysed protein was significantly faster than from intact protein. The enzymatic activity of pepsin in the stomach and of trypsin, chymotrypsin, carboxypeptidases A and B in the different segments of the intestine changed significantly with increasing inclusion of potato protease inhibitors in the diet.