Growth response and resistance to Streptococcus iniae of Nile tilapia, Oreochromis niloticus, fed diets containing different levels of wheat distillerʹs dried grains with solubles with or without lysine supplementation

A study was conducted to evaluate the effect of dietary levels of wheat distillerʹs dried grains with solubles (DDGS) with or without lysine supplementation on growth, body composition, hematology, immune response, and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus iniae challenge. Nine isonitrogenous, isocaloric diets were formulated to contain 0 (control), 100, 200, 300 and 400 g/kg wheat DDGS without (W0–W400) and with (WL100–WL400) lysine supplementation to a level equal to that of the control diet as partial replacement of a combination of soybean meal (SBM) and maize meal (MM) on an equal protein basis. Each diet was fed to juvenile Nile tilapia (3.92 ± 0.07 g) in triplicate aquaria twice daily to apparent satiation for 10 weeks. Fish fed W400 had lower (P<0.05) weight gain (WG), feed efficiency ratio (FER), and protein efficiency ratio (PER) compared with those fed the control diet. Supplementation of lysine to the 400 g/kg wheat DDGS diet (WL400) increased (P<0.05) WG, FER, PER to levels similar to those fed control diet. The values of these variables did not differ among fish fed W0–W300 and WL100–WL400. No differences (P>0.05) were observed among whole body moisture, protein and fat of fish receiving various diets. Whole body ash tended to increase with increasing levels of dietary wheat DDGS, but the differences were not always significant. Hematological and immunological parameters, the average number of days to first mortality after S. iniae challenge and cumulative mortality 4 weeks post challenge were not affected (P>0.05) by dietary treatments. Results of this study suggest that wheat DDGS can be incorporated in Nile tilapia diets at a level of 300 g/kg as a substitute, on an equal protein basis, for a combination of SBM and MM without requiring lysine supplementation. The inclusion level of wheat DDGS can be increased to at least 400 g/kg (highest level evaluated) if lysine was supplemented to a level equal to that of the control diet.