Sucrose supplementation mitigates heat stress-induced alterations in rumen metabolism and immunity in dairy cows.

Rapid global warming is affecting the metabolic and immune responses of dairy cows, making heat stress a major challenge in the industry. This study aimed to develop nutritional strategies to mitigate these effects. Sucrose has been identified as a carbohydrate that not only provides immediate energy to the rumen. Specifically, we investigated whether sucrose supplementation could alleviate heat stress-induced changes in rumen metabolism and blood immune parameters. A total of 12 Holstein cows were used in this study. All cows were initially maintained under the optimal temperature period (OTP, n = 12). They were then assigned to either the high-temperature period control group (HTP-CON, n = 6) or the high-temperature period treatment group (HTP-TRT, n = 6). The feeding trial lasted for four weeks. Heat stress reduced milk yield by 22.36%, and sucrose supplementation tended to attenuate this reduction to 10.75%; heat stress decreased milk yield, whereas sucrose supplementation has minor mitigating effect on milk yield reduction. Furthermore, heat stress altered rumen metabolites, leading to metabolic imbalances, particularly in amino acid and fatty acid metabolism. Sucrose supplementation improved amino acid metabolic pathways, including phenylalanine and glutamate metabolism, which are essential for immune and metabolic homeostasis. Key metabolites such as aspartic acid, tyrosine, and isobutyrate were restored. Additionally, heat stress induced an inflammatory response, increasing the proportion of Th1 cells and upregulating IL-1β and IL-2 expression in PBMCs. Sucrose supplementation alleviated inflammation by reducing pro-inflammatory cytokine expression and normalizing the Th1 cell proportion. In conclusion, sucrose supplementation improved the resilience of dairy cows by alleviating metabolic imbalances and inflammatory responses caused by heat stress. These findings enhance our understanding of the relationship between immunity and metabolism under environmental stress and support the development of improved dairy management strategies.