Effects of betaine on growth performance and intestinal health of rabbits fed different digestible energy diets

Abstract An experiment was conducted to determine the effects of betaine on growth performance and intestinal health in rabbits fed diets with different levels of digestible energy. During a 36-d experiment, a total of 144 healthy 35-d-old weaned New Zealand white rabbits with a similar initial body weight (771.05 ± 41.79 g) were randomly distributed to a 2 × 3 factorial arrangement. Experimental treatments consisted of two levels of digestible energy (normal: 10.20 and low: 9.60 MJ/kg) and three levels of betaine (0, 500, and 1,000 mg/kg). Results indicated that rabbits fed the diet with low digestible energy (LDE) had reduced body gain/feed intake on days 1 to 14 and 1 to 36 (P < 0.05), increased the apparent total tract digestibility (ATTD) of neutral detergent fiber, acid detergent fiber (ADF), and n-free extract, and decreased the ATTD of gross energy (GE), crude fiber, and organic matter (OM; P < 0.05). The LDE diet upregulated the gene abundance levels of duodenum junctional adhesion molecule-3 (JAM-3) and downregulated the ileum toll-like receptor 4, myeloid differentiation factor 88, and interleukin-6 (IL-6; P < 0.05). Activities of amylase, lipase, trypsin, and the immunoglobulin M content in the jejunum were decreased in the LDE treatment group (P < 0.05). Dietary betaine supplementation increased the ATTD of GE, dry matter (DM), ADF, and n-free extract by LDE (P < 0.05). The villus height, crypt depth, and goblet cell numbers were decreased, and the villus–crypt ratio was increased in the duodenum (P < 0.05). The gene abundance levels of duodenum IL-2 were downregulated, and the duodenum JAM-2 and JAM-3 were upregulated (P < 0.05). Furthermore, the addition of betaine to the LDE diet increased the ATTD of GE, DM, and OM in rabbits (P < 0.05). Gene abundance levels of ileum IL-6 and duodenum JAM-3 were upregulated (P < 0.05). In summary, LDE diets can reduce the activity of intestinal digestive enzymes and decrease the ATTD of nutrients. However, the addition of betaine to LDE diets improved the intestinal barrier structure and nutrient ATTD in rabbits, with better results when betaine was added at an additive level of 500 mg/kg.