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Bovine mastitis is among the most serious disease in the dairy industry and brings huge economic losses due to the decrease in milk quality and quantity. Betaine, a naturally occurring compound, possesses several pharmacological activities including anti-inflammatory and anti-oxidant ability, but whether betaine has protective effects on bovine mastitis is unknown. The aim of this study is to investigate the effect of betaine on mastitis and further discover its feasible molecular mechanism in lipopolysaccharide (LPS)-stimulated bovine mammary epithelial cells (BMECs). BMECs were pre-treated with or without betaine or LPS. Cell viability was measured with CCK-8 to examine the cytotoxicity. The levels of pro-inflammatory cytokines were measured by ELISA kits. Western blotting was used to explore the regulation of genes associated with inflammatory and oxidative stress genes. The results showed that LPS treatment significantly increased the production of pro-inflammation (IL-1β, IL-6 and TNFα), enhanced malondialdehyde (MDA) content, reduced superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, and markedly up-regulated the protein expression of COX2 and iNOS (p < 0.05). However, betaine pre-treatment remarkably restored the above phenomenon compared with the LPS group. Additionally, we also observed that betaine exposure significantly restricted LPS-induced the phosphorylation of IκB and NF-κB p65 (p < 0.05). Moreover, pre-treatment of BMECs with betaine abolished LPS-induced the increase of Nrf2 and HO-1 protein levels (p < 0.05). These results confirm that betaine can alleviate LPS-induced inflammatory response and oxidative damage by modulating NF-κB and Nrf2 signalling pathways. Betaine alleviated the production of pro-inflammation cytokines (IL-1β, IL-6 and TNFα) in BMECs after LPS stimulation. Betaine restored LPS-elicited nuclear factor kappa-B (NF-κB) signalling pathway activity. Betaine recovered LPS-induced the activity of SOD and GSH-Px and MDA content. Betaine inhibited the increase of protein expression of Nrf2 and HO-1 challenged with LPS. [ABSTRACT FROM AUTHOR]