Effects of threonine supplementation in poultry by-product meal (petfood grade) replacement diet on growth performance, intermediary metabolism and immunity response in largemouth bass (Micropterus salmoides)

In order to investigate the effects of different dietary threonine levels on growth performance, glucose and lipid metabolism, immunity and utilization rate of poultry by-product meal (petfood grade) in largemouth bass(Micropterus salmoides), three isonitrogenous and isolipid diets were designed using M. salmoides with an initial body weight of (4.16±0.06) g as the research subjects (TC diet: threonine control group, LT diet: low threonine group and TS diet: threonine supplementation group) were cultured for for 8 weeks. Present results showed that compared with the TC diet, the LT diet significantly decreased the growth performance, feed efficiency and body nutrient composition, threonine addition could promote those differential effects caused by fishmeal totally substituted by poultry by-product meal. Moreover, the LT diet also suppressed the concentration of plasma nutrients and free amino acids compared with the control diet. TS diet had significant effects on elevating the plasma free amino acids concentration and made no notable difference compared to the TC diet. The mRNA expression level demonstrated that threonine supplementation markedly ameliorated the inhibition of anabolism, aggravation of catabolism and cellular inflammation caused by complete replacement of fishmeal with poultry by-product meal. Studies have shown that appropriate threonine supplementation could promote the growth performance by improving nutrient anabolism and immune response and inhibiting catabolism in M. salmoides.