Oregano essential oil enhanced body weight and well-being by modulating the HPA axis and 23-nordeoxycholic acid of cecal microbiota in Holstein steers under cold stress.

BACKGROUND: Prolonged exposure to cold stress in cattle increases basal energy consumption and impedes optimal production. Consequently, herds require adequate attention during cold, extended winters to alleviate cold stress and maintain profitability. This study investigated the effects of oregano essential oil (EO) on body weight (BW), well-being, blood parameters, and cecal microbiota. Eighteen steers were randomly divided into two groups (n = 9) and fed either a basal diet (CK) or the same diet supplemented with 20 g/(d·head) EO for 270 days. RESULTS: EO increased BW by increasing cecal microbial abundance and carbohydrate metabolism CAZymes, leading to elevated the total volatile fatty acids (VFA) levels. Cold stress activated the HPA axis, and mitigated stress by reducing serum levels of cortisol (COR), corticosterone (CORT), adrenocorticotropic hormone (ACTH), and dopamine (DA). EO increased well-being by decreasing viral species without apparent contribution to drug or antibiotic resistance development, and cecal metabolites were primarily enriched in growth, carbohydrate metabolism, and amino acid metabolism pathways. Specifically, tryptophan metabolism (2-picolinic acid, quinolinic acid, and oxindole) enhanced steer well-being by increasing antioxidants (superoxide dismutase (SOD), peroxidases (POD), and glutathione (GSH)) and reducing inflammatory factors (interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)) following EO treatment. Notably, low-abundance microorganisms (s_Streptomyces_gardneri, s_Paenibacillus_sp._S09, and s_Nocardia_sp._Root136) may play a significant role in growth and immunity. CONCLUSION: These findings provide fundamental insights into how EO alleviates cold stress by modulating the HPA axis, promotes growth and well-being of steers under cold stress by influencing mediates tryptophan metabolism of cecal microbiota in Holstein steers.