Protein level affects the relative lysine requirement of growing rainbow trout (Oncorhynchus mykiss) fry

摘要

The effect of two digestible protein levels (310 and 469 g/kg DM) on the relative lysine (Lys; g Lys/kg DM or g Lys/100 g protein) and the absolute Lys (g Lys intake/kg0p"75 per d) requirements was studied in rainbow trout fry using a dose-response trial. At each protein level, sixteen isoenergetic (22-23 MJ digestible energy/kg DM) diets were tested, involving a full range (2-70 g/kg DM) of sixteen Lys levels. Each diet was given to one group of sixty rainbow trout fry (mean initial body weight 0p"78 g) reared at 15pC for 31 feeding d. The Lys requirements were estimated based on the relationships between weight, protein, and Lys gains (g/kg0p"75 per d) and Lys concentration (g/kg DM or g/100 g protein) or Lys intake (g/kg0p"75 per d), using the broken-line model (BLM) and the non-linear four-parameter saturation kinetics model (SKM-4). Both the model and the response criterion chosen markedly impacted the relative Lys requirement. The relative Lys requirement for Lys gain of rainbow trout estimated with the BLM (and SKM-4 at 90 % of the maximum response) increased from 16p"8 (19p"6) g/kg DM at a low protein level to 23p"4 (24p"5) g/kg DM at a high protein level. However, the dietary protein content affected neither the absolute Lys requirement nor the relative Lys requirement expressed as g Lys/100 g protein nor the Lys requirement for maintenance (21 mg Lys/kg0p"75 per d).