Supplementation of Rosemary Extract Improves Lactation Performance and Rumen Function in Dairy Buffaloes Under Hot Weather

Rosemary extract (RE), rich in carnosic and rosmarinic acid, which have antibacterial/antioxidant/anti-inflammatory effects, is a potential natural feed supplement for heat-stressed dairy buffaloes. This study systematically evaluated dietary RE effects on dairy buffaloes during hot weather. Twenty Mediterranean dairy buffaloes were randomly allocated into two groups for a 35-day trial: the control (CON) group receiving a basal diet, and the RE group receiving the same basal diet supplemented with 20 g/d of RE. Results showed RE tended to reduce buffalo body surface temperature; increased milk production, 4% fat-corrected milk, milk protein, lactose, and solids-not-fat; and optimized milk fatty acid profiles. In regard to blood, the RE group exhibited higher catalase activity, total antioxidant capacity, and concentrations of immunoglobulin A and M, together with lower concentrations of the pro-inflammatory cytokines interleukin-1β and tumor necrosis factor-α. Additionally, RE markedly elevated concentrations of total volatile fatty acid, acetate, propionate, and butyrate; improved microbial α-diversity indices (Sobs and Ace); and increased the abundances of Rikenellaceae_RC9_gut_group and Butyrivibrio spp., as well as the enrichment of multiple genera belonging to the family Lachnospiraceae. In conclusion, supplementing the diet of heat-stressed dairy buffaloes with 20 g/d of RE improves milk production and composition-related performance by optimizing the rumen ecosystem and enhancing systemic health status, with these effects observed as short-term responses under the conditions of the present study.