To investigate the effects of supplemental monensin administration on the metabolic responses of dairy cows, a systematic review and dose-response meta-analysis was conducted. Initially, 604 studies were identified through comprehensive database searches, including Google Scholar, Scopus, Science Direct, and PubMed, using keywords related to dairy cows, monensin, and metabolic outcomes. After a 2-stage screening process, 51 articles with a total of 60 experiments were selected for meta-analysis based on criteria such as the study implementation date between 2001 and 2022, the presence of a control group that did not receive monensin supplementation, the reporting of at least one outcome variable, and the presentation of means and corresponding errors. The meta-analysis used the one-stage random effects method, and sensitivity analyzes were performed to assess the robustness of the results. The results showed that the administration of monensin at a dosage of 19-26 ppm was inversely related to methane emissions and that the administration of monensin at a dosage of 18-50 ppm resulted in a significant decrease in dry matter intake (DMI). Administration of monensin at doses of 13-28 and 15-24 ppm also resulted in a significant decrease in ruminal acetate proportion and an increase in propionate proportion, respectively, with no effects on ruminal butyrate, NH3, or pH levels. There were no effects on blood parameters or nitrogen retention, but a significant negative correlation was observed between monensin supplementation and fecal nitrogen excretion. Based on the analysis of all variables evaluated, the optimal dose range of monensin was estimated to be 19-24 ppm.

The aim of this study was to conduct a comprehensive review with meta-analysis to determine the effects of the dose–response relationship between monensin supplementation and dairy cow performance and milk composition. Results from 566 full-text articles and 48 articles with 52 studies were meta-analyzed for pooled estimates. Monensin supplementation up to 23 ppm increased milk production, with the optimal dose being 12.6 ppm. Monensin supplementation at doses ranging from 16 to 96 ppm increased milk production in the prepartum phase (− 28 to 0 day relative to calving). From 60 to 150 DIM, monensin supplementation up to 21 ppm had a significant positive effect on this outcome, while supplementation in the 37 to 96 ppm range caused a decrease in this variable. At 0 to 60 and > 150 DIM, monensin supplementation had no effect on milk yield. At dosages of 22 to 96 ppm, 12 to 36 ppm, and below 58 ppm and 35 ppm, respectively, monensin supplementation resulted in significant decreases in dry matter intake (DMI), milk protein percentage, milk fat percentage, and milk fat yield. Overall, based on the results of this meta-analysis and considering all variables, the recommended optimal dose of monensin could be about 16 ppm.

This narrative review summarizes the role of microminerals in mitigating heat stress (HS) in dairy cows, with a focus on antioxidant defense, immune function, and metabolic regulation. A systematic literature search (2000–2025) in Scopus, Google Scholar, and PubMed included only studies conducted on dairy cows under HS. Evidence indicates that chromium, selenium, zinc, copper, cobalt, and combined micromineral supplements affect production performance, physiological responses, and overall health in heat-stressed dairy cattle. Chromium supplementation has been widely studied for its role in enhancing energy metabolism, contributing to increased dry matter intake (DMI), milk yield, and better heat tolerance. Selenium, as part of selenoproteins, supports antioxidant capacity, thermotolerance, and immune function, though its effect on milk yield remains inconsistent. Zinc helps antioxidant defense, reduces inflammation, and maintains calcium homeostasis, but its impact on production outcomes is unclear. Copper supports immune and antioxidant functions, with results influenced by dose, source, and animal physiological status. Cobalt, essential for vitamin B12 synthesis and rumen microbial activity, is linked to higher milk and milk fat production; however, excessive intake may impair milk protein synthesis. Multi-micromineral strategies show synergistic benefits, including improved milk composition, udder health, immune function, and reproductive performance under HS. Nevertheless, responses vary with mineral form, dosage, physiological stage, and environmental conditions. In conclusion, micromineral supplementation represents a promising nutritional strategy to alleviate HS in dairy cattle. Yet, variability in outcomes highlights the need for further research to define optimal dosing, clarify mineral interactions, and establish practical guidelines for sustainable productivity and animal welfare in heat-stressed systems.