THE MODULATORY EFFECT OF DIETARY BETAINE ON INTESTINAL ABSORPTIVE CAPACITY, LIPOGENESIS AND EXPRESSION OF LIPID METABOLISM- AND GROWTH-RELATED GENES IN NILE TILAPIA FED ON SOYBEAN MEAL-BASED DIET

Abstract

The current experiment was randomly designed in a 2×2 factorial design. Two dietary protein sources were utilized; fish meal and soybean meal; with betaine incorporation to both of them. This study aimed to determine the impact of incorporation of betaine into soybean meal-based (SBM) diets through its effects on growth performance, intestinal healthiness and expression of some lipid metabolism- and growth-related genes. Fish (19.84±0.20 g) were stocked in 12 aquaria and allotted into triplicate four groups (10 fish per aquarium). Four test diets were formulated to contain fish meal (FM) as a positive control, FM with betaine (FM + Betaine), SBM diet and SBM with betaine (SBM + Betaine), respectively. After 60 days, dietary betaine improved the growth performance of fish fed FM or SBM as revealed by higher final body weight, body weight gain and average daily gain and lower feed conversion ratio. Monitoring the whole-body composition revealed that addition of betaine to diet relatively augmented flesh protein content and reduced its fat content. In addition, betaine incorporation in diets significantly (P<0.05) increased the intestinal villi length especially in the jujenal portion as well as the numbers goblet cells. Furthermore, betaine had a downregulating effect on expression of lipid metabolism-related genes, fatty acid synthetase (Fas) and lipoprotein lipase (Lpl) and upregulating effect on insulin growth like factor-1 (Igf-1) gene in liver. It could be concluded that dietary supplementation of betaine incorporation to soybean-based diets enable nutritionists to substitute FM in fish diet. Also, betaine could improve growth performance, carcass quality (through increasing protein and decreasing lipid in fish) and enhance intestinal functions capability. Key words: Betaine; growth performance; insulin like growth hormone factor; lipid metabolism related genes; Nile tilapia; soybean meal