Effects of replacement of dietary rapeseed meal by distiller's dried grains with solubles (DDGS) on growth performance, muscle texture, health and expression of muscle-related genes in grass carp (Ctenopharyngodon idellus)

The objective of this study was to compare the biological value between dietary rapeseed meal (RSM) and maize distiller's dried grain with solubles (DDGS) in juvenile grass carp (initial body weight: 5.38 +/- 0.18 g) through a 60 d feeding trial. A control diet containing 28% RSM and 4 experimental diets containing 10.0, 20.6, 30.9, and 41.1% DDGS to replace RSM were formulated. The results showed that dietary DDGS inclusion significantly affected the growth performance including final body weight, SGR, FR, and FE, which all showed a quadratic trend as DDGS level increased. The optimal dietary DDGS level was estimated as 28.2% and 32.1%, respectively, based on the quadratic models of SGR and FE. As dietary DDGS level increased, hepatosomatic index decreased linearly (P = 0.000), while condition factor decreased and then increased in a quadratic model (P = 0.020). The mesenteric fat index showed a trend opposite to condition factor responding to DDGS level. Serum ALT, AST, and triglyceride levels decreased linearly with increasing dietary DDGS. As DDGS inclusion level increased, collagen content in raw muscle increased linearly, while muscle texture including hardness, gumminess and chewiness decreased linearly (P = 0.000). Muscle fiber diameter linearly increased with DDGS level (P = 0.000), while fiber density decreased in a quadratic model (P = 0.008). Apparent digestibility coefficients (ADCs) of dry matter and energy decreased at higher DDGS inclusion level (30.9% or more) while ADC of protein increased first and then decreased. The relationship between dietary DDGS inclusion level and expression of fgf6a, myhc, mrf4, mstn, and myf5 were explained by quadratic regression models. fgf6b expression decreased with DDGS level. Overall, Dietary DDGS replacing RSM showed positive effects on growth performance, lipid metabolism and muscle collagen content, while negatively affected hardness of muscle.