Dietary Betaine improves the intestinal health and growth performance of heat-stressed growing rabbits in summer.

The main objective of this study is to explore how various amounts of Bet affect growth performance, nutritional digestibility, and intestinal health of growing rabbits under high-temperature environment in summer. A total of 150 healthy 35-day-old weaned QiXing meat rabbits (Germany White rabbit × Sichuan White rabbit) were individually assigned to five treatments, each with 30 replicates and one rabbit per replicate. The control group was fed with basal diet, while the experimental group received a basal diet supplemented with 0.75, 1.0, 1.5, and 2.0 g Bet/kg diet, respectively. During the whole experimental stage, all animals can eat and drink freely, and they were kept in the rabbit house with an average daily temperature of 30.11 ± 0.5℃ and a relative humidity of 71.02 ± 5.07%. The results showed that dietary supplementation with 1.5 g/kg Bet increased average daily gain and decreased feed to gain ratio from day 1 to day 42 as compared to the control group (P < 0.05), adding 0.75, 1.0, 1.5 and 2.0 g/kg Bet increased average daily gain and average daily feed intake from day 22 to day 42 (P < 0.05), and increased the nutritional digestibility of acid detergent fiber (P < 0.05). Furthermore, dietary supplementation with 1.0, 1.5 and 2.0 g/kg Bet reduced D-lactate content and diamine oxidase activity in the serum (P < 0.05). Compared to the control group, supplementation of 0.75 and 1.5 g/kg Bet improved glutathione peroxidase activities in the duodenum and ileum, adding 0.75, 1.0, 1.5 and 2.0 g/kg Bet decreased malonaldehyde content in the duodenum and jejunum (P < 0.05). Moreover, the supplement of 1.5 and 2.0 g/kg Bet upregulated JAM-2 and IL-10 levels in the jejunum (P < 0.05). In conclusion, supplementation with Bet in the diet improves the growth performance, nutrient digestibility and intestinal health of growing rabbits under high-temperature environments, and the 1.5 g Bet/kg diet group has the best effect.