Availability and utilisation of free lysine in rainbow trout (Oncorhynchus mykiss) -: 2.: Comparison of L-lysine • HCl and L-lysine sulphate

A basal diet, aiming at a low lysine concentration (9 g/kg DM), was formulated with wheat gluten as the sole source of protein. Lysine concentration was increased in two steps of approximately 4 g/kg DM each by use of either L-lysine . HCl or L-lysine sulphate. Each diet was fed at a restricted rate to three groups of 20 rainbow trout for 56 days. Faecal samples were collected via a sedimentation system and availability was determined using acid-insoluble ash as a marker. Retention was measured via comparative whole body analysis. Faecal lysine excretion was not affected by lysine supplementation. Body weight gain and gain/feed ratio, as well as the composition of body weight gain, were significantly affected by dietary lysine concentration but not by lysine source. The utilisation of supplemental lysine, calculated as Delta retained/Delta digested X 100, was, on average, 68% and was not significantly different between the two lysine sources (P = 0.62). It is concluded that both lysine sources are equally available to rainbow trout. (C) 2000 Elsevier Science B.V. All rights reserved.