Effect of dietary supplementation of betaine on productive performance, egg quality and jejunal tight junction-related gene expression in laying hens raised under hot environmental conditions

The objective of this experiment was to investigate the effect of dietary supplementation of betaine on productive performance, egg quality, and jejunal tight junction-related gene expression in laying hens raised under hot environmental conditions. A total of 216 laying hens of 32 weeks of age were allotted to 1 of 3 dietary treatments with 6 replicates and 12 hens per replicate in a completely randomized design. A commercial-type basal diet was prepared, and 3.0 or 6.0 g/kg of betaine was supplemented to the basal diet. Diets were fed to hens for 6 weeks. Hens were raised during the hot season (the end of July to the middle of September), and the average daily room temperature and relative humidity were 25.8 ± 2.0 °C and 74.8 ± 7.3%, respectively. At the end of the experiment, 2 hens per replicate were euthanized to collect jejunal mucosa samples. Results indicated that a tendency (linear, P = 0.094) for increased hen-day egg production was observed as inclusion amounts of betaine in diets were increased. Increasing inclusion amounts of betaine in diets decreased (linear, P < 0.05) broken and shell-less egg production. Egg quality was not influenced by dietary treatments, except for a quadratic increase (P < 0.05) in eggshell strength by increasing inclusion amounts of betaine in diets. Increasing inclusion amounts of betaine in diets increased the expressions of occludin (OCLN; linear, P < 0.01) and claudin-1 (CLDN-1; linear, P = 0.062), but decreased the expressions of zonula occludens-1 (ZO-1; linear and quadratic, P < 0.05) and junctional adhesion molecule B (JAM-2; linear and quadratic, P < 0.01) in the jejunal mucosa. In conclusion, dietary supplementation of betaine improves laying performance and selectively modifies in jejunal tight junction-related gene expressions in laying hens raised under hot environmental conditions.