Effects of Dietary Betaine on the Laying Performance, Antioxidant Capacity, and Uterus and Ovary Function of Laying Hens at the Late Stage of Production

Simple Summary Egg is a staple food in the human diet, containing all nutrients except vitamin C and dietary fibre. As the layers age, egg production and egg quality drop. Betaine is a natural compound widely found in many plants and animals, such as beets, spinach, wheat, and shellfish. It is readily available and cheap. Many studies have addressed betaine as a valuable dietary addition to alleviating inflammation, apoptosis, and oxidative stress. However, it is unclear whether dietary betaine consumption can improve the laying performance during the late-laying period. In this study, betaine was added to the diet of 65-week-old Jinghong-1 layers, whose laying performance declines after 60 weeks and can be below 80% at 80 weeks when the commercial cycle ends. We found that dietary betaine increased egg production and eggshell thickness. Our data further suggested that dietary betaine improved the function of the uterus and ovary, manifested by increased antioxidation capacity, higher expression of calcification-associated genes and hormone receptors, and decreased expression of pro-apoptotic genes. Considering the tendency to keep hens in production longer and the hens' welfare, this study may offer a partial solution to the problem of egg production and quality.Abstract Betaine has been found to alleviate oxidative stress, inflammation, and apoptosis. However, whether dietary betaine can protect late-laying hens against these adverse effects is unknown. Here, 270 65-week-old Jinghong-1 laying hens were randomly divided into the Control, 0.1% Betaine, and 0.5% Betaine groups and fed a basal diet, 0.1%, and 0.5% betaine supplemented diet, respectively. The trial lasted for seven weeks. Birds that consumed 0.5% betaine laid more eggs with thicker eggshells. Accordingly, uterine reduced glutathione (GSH), glutathione peroxidase (GSH-PX), and ovarian superoxide dismutase (SOD) contents were increased. The uterine calcium ion content and the mRNA expression of ovalbumin, ovotransferrin, and carbonic anhydrase two were increased. Moreover, ovarian IL-1 beta, Caspase-1, Caspase-8, and Caspase-9 mRNA expressions were decreased; luteinising hormone receptor (LHR) and follicle-stimulating hormone receptor mRNA expressions were increased. Furthermore, dietary betaine decreased the ovaries' mRNA expression of DNA methyltransferase 1 (DNMT)1, DNMT3a, and DNMT3b. The methylation level at the promoter region of ovarian LHR decreased. These results indicated that dietary betaine consumption with a concentration of 0.5% could increase the laying rate and the eggshell thickness during the late-laying period. The underlying mechanism may include antioxidative, anti-apoptosis, and hormone-sensitivity-enhancing properties.