Effect of dietary betaine on growth performance, antioxidant capacity and lipid metabolism in blunt snout bream fed a high-fat diet

An 8-week feeding experiment was conducted to determine the effect of dietary betaine levels on the growth performance, antioxidant capacity, and lipid metabolism in high-fat diet-fed blunt snout bream (Megalobrama amblycephala) with initial body weight 4.3 +/- 0.1 g [mean +/- SEM]. Five practical diets were formulated to contain normal-fat diet (NFD), high-fat diet (HFD), and high-fat diet with betaine addition (HFB) at difference levels (0.6, 1.2, 1.8%), respectively. The results showed that the highest final body weight (FBW), weight gain ratio (WGR), specific growth rate (SGR), condition factor (CF), and feed intake (FI) (P < 0.05) were obtained in fish fed 1.2% betaine supplementation, whereas feed conversion ratio (FCR) was significantly lower in the same group compared to others. Hepatosomatic index (HSI) and abdominal fat rate (AFR) were significantly high in fat group compared to the lowest in NDF and 1.2% betaine supplementation, while VSI and survival rate (SR) were not affected by dietary betaine supplementation. Significantly higher (P < 0.05), plasma total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), aspartate transaminase (AST), alanine transaminase (ALT), cortisol, and lower high-density lipoprotein (HDL) content were observed in HFD but were improved when supplemented with 1.2% betaine. In addition, increase in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) in 1.2% betaine inclusion could reverse the increasing malondialdehyde (MDA) level induced by HFD. Based on the second-order polynomial analysis, the optimum growth of blunt snout bream was observed in fish fed HFD supplemented with 1.2% betaine. HFD upregulated fatty acid synthase messenger RNA (mRNA) expression and downregulated carnitine palmitoyltransferase 1, peroxisome proliferator-activated receptor alpha, and microsomal triglyceride transfer protein mRNA expression; nevertheless, 1.2% betaine supplementation significantly reversed these HFD-induced effects, implying suppression of fatty acid synthesis, beta-oxidation, and lipid transport. This present study indicated that inclusion of betaine (1.2%) can significantly improve growth performance and antioxidant defenses, as well as reduce fatty acid synthesis and enhance mitochondrial beta-oxidation and lipid transportation in high-fat diet-fed blunt snout bream, thus effectively alleviating fat accumulation in the liver by changing lipid metabolism.