Abstract
BACKGROUND: Mare's milk has gained attention as a functional food due to its bioactive compounds and potential microbiome-modulating properties. This systematic review evaluated the evidence on its potential role in gut microbiome restoration and immune modulation following COVID-19, particularly in pediatric and maternal populations. METHODS: PubMed/MEDLINE, Scopus, Web of Science, and Embase were systematically searched for studies investigating mare's milk or koumiss and their effects on gut microbiota, immune responses, inflammatory markers, or gastrointestinal outcomes. RESULTS: Eight studies were included: five examined COVID-19-associated gut microbiome alterations, and three investigated the biological effects of mare's milk or fermented mare's milk. COVID-19 was consistently associated with reduced microbial diversity, depletion of beneficial bacteria, and enrichment of opportunistic pathogens, with some changes persisting after recovery. CONCLUSIONS: Koumiss demonstrates biologically plausible microbiome-modulating and immunoregulatory properties that may support recovery from COVID-19-associated gut dysbiosis. However, current evidence remains indirect, and clinical studies are needed before recommendations can be made.