Dietary betaine supplementation improved egg quality and gut microbes of laying hens under dexamethasone-induced oxidative stress.

Oxidative stress is a frequent concern in the breeding of laying hens, and limit the healthy development of poultry. Dexamethasone (DXM) has been demonstrated to induce oxidative stress. Conversely, betaine is an alkaloid with a potent antioxidant activity. The study was designed to investigate the ameliorative effect of betaine on DXM-induced oxidative stress in laying hens. The results revealed that DXM treatment significantly decreased laying rate, shell strength, albumen height, Haugh unit, egg weight, folk weight and albumen weight, alongside increased malondialdehyde (MDA) and decreased total antioxidant capacity (T-AOC) in serum and liver (P < 0.05). In contrast, dietary betaine addition reversed those parameters mentioned above (P < 0.05). Hepatic RNA-seq analysis showed that there existed 110 up- and 88 down-regulated genes in DXM group when compared with the control. Meanwhile there were 117 upregulation and 169 downregulation genes in BT group when compared with DXM group. Besides, we found that dietary betaine addition significantly down-regulated cell adhesion molecules, glycerolipid metabolism and glycolysis gluconeogenesis pathways. In addition, a total of 44 and 94 differential metabolites were identified respectively from Con vs. DXM and DXM vs BT. More importantly, dietary betaine addition significantly increased the levels of pantothenic acid, gamma-Aminobutyric acid, equol and choline, all of which were related to antioxidant and anti-inflammatory properties. Furthermore, gut microbiota analysis indicated that the Chao and Observed_species indexes were remarkably higher in BT group (P<0.05). Heatmap analysis revealed that Subdoligranulum, Prevotella, Blautia, YRC22, Bacteroides, Ruminococcus and Coprococcus were notably restored in BT group (P<0.05). Taken together, our findings collectively illustrate that dietary betaine addition could attenuate DXM-induced oxidative stress, improve egg quality and gut microbes of laying hens.