Functional Classification of Tropical Cattle Feeding Systems Reveals Consistent Associations with Dairy Lipid Quality, Enteric Methane Emissions, and Preclinical Metabolic Outcomes: A Multi-Study Narrative Synthesis.

Administrative labels such as "organic" or "pasture-fed" animal food products inadequately capture the biological complexity of dairy production systems and consequently fail to differentiate potentially meaningful associations with nutritional quality, environmental impact and consumers' health. We developed a functional classification framework based on three measurable traits: (1) botanical diversity, (2) concentrate dependence, and (3) input intensity, and applied it to six observational and/or experimental studies from tropical Mexico (n = 109 farms across Yucatán, Chiapas, and Colima federal states). Animal production systems were categorized as: (a) biodiverse grazing (silvopastoral, organic, or traditional grazing; >15 plant species or 8-14 species with concentrate < 25% dry matter intake and no synthetic inputs) or (b) conventional (monoculture/indoor systems; <5 plant species or 6-10 species with concentrate >40% with a use of agrochemicals). Biodiverse grazing systems produced lower daily milk yields (6.1 vs. 7.7 L d-1; p < 0.0001) but yielded milk with more favorable cardiovascular lipid indices: atherogenic index (AI: 1.6-2.2 vs. 1.9-2.5), thrombogenic index (TI: 2.3-2.7 vs. 2.3-3.1), and health promotion index (HPI: 0.46-0.67 vs. 0.40-0.54). Artisan cheese from biodiverse systems contained substantially higher concentrations of tocopherols (127 vs. 77 mg 100 g-1 DM) and monoterpenes (460-475 vs. 111-126 ng kg-1). An intensive silvopastoral system reduced enteric methane emissions by 18.2% (376 vs. 460 g d-1; p < 0.05) and by 21.3% per unit dry matter intake (24.0 vs. 30.5 g kg-1 DMI; p < 0.0001). Forage nutritional quality (crude protein, neutral detergent fiber, acid detergent fiber) varied by species and season, with these parameters influencing estimated methane emissions. In a C57BL/6 murine model of high-fat diet-induced obesity, milk from biodiverse silvopastoral systems attenuated body weight gain (30.5 vs. 36.8 g; p < 0.05), preserved glucose tolerance (AUC: 32,616 vs. 45,248), nearly eliminated hepatic macrovesicular steatosis, and promoted smaller adipocyte size (1863 vs. 3880 µm2; p < 0.05) compared with conventional milk. These findings suggest that functional ecological traits provide a useful framework for evaluating dairy systems, with biodiverse grazing offering a potential convergence of environmental sustainability and preclinical health benefits. Nevertheless, external validation across diverse tropical regions and direct human intervention trials remain necessary to establish generalizability, and the associations identified should be considered hypothesis-generating rather than confirmatory.