Phytochemicals in Ruminant Diets: Mechanistic Insights, Product Quality Enhancement, and Pathways to Sustainable Milk and Meat Production—Invited Review

Dietary phytochemicals, primarily derived from grasses, legumes, and agro-industrial byproducts of plant origin, encompass distinct chemical classes such as polyphenols (including tannins, flavonoids, and other polyphenol compounds), saponins, organosulfur compounds, and essential oils (largely composed of terpenoids and phenylpropanoids). These compounds can function as rumen modifiers, antimethanogenic agents, anthelmintics, growth promoters, stress mitigators, and biopreservatives in ruminant production systems. Thus, they improve feed efficiency, nutrient utilization, and nitrogen retention while mitigating greenhouse gas emissions. In dairy systems specifically, phytogenic feedstuffs enhance milk yield and composition by enriching conjugated linoleic acids (CLAs), omega-3 fatty acids, and antioxidant compounds, leading to superior nutritional and oxidative stability. In meat production systems, they improve tenderness, flavor and shelf life through reduced oxidation and enhanced muscle metabolism. Despite these benefits, dose optimization, bio-efficacy, and species-specific responses remain critical research priorities. Use of phytogenic-based feeding strategies aligns with global sustainability goals by reducing reliance on feed additives, promoting environmentally resilient and circular food systems. This review synthesizes emerging evidence on the mechanisms, production outcomes, and functional benefits of dietary phytochemicals, providing a scientific framework for their strategic application in sustainable ruminant milk and meat production.