Resumen
Vitamin K2 (menaquinones) has gained increasing scientific interest due to its emerging physiological roles, yet food-composition data remain incomplete. Among menaquinones, menaquinone-4 (MK-4) is the predominant analogue in bovine muscle, but no study to date has directly compared MK-4 concentrations in beef obtained from different production systems. This study quantified MK-4 levels by high-performance liquid chromatography with ultraviolet detection (HPLC-UV) in beef from steers raised either under a well-managed, ecologically aligned grazing system or a grain-finished system. Fatty acid composition was additionally assessed to independently contextualize the novel MK-4 determinations. Beef from the grazing system exhibited markedly higher MK-4 concentrations (15.40 ± 2.54 µg/100 g) than grain-finished beef (2.30 ± 0.61 µg/100 g; P < 0.001). Fatty acid profiles followed established patterns, with grazing increasing ALA, EPA, DHA, and total n-3 PUFA while reducing LA and total n-6 PUFA, yielding an n-6/n-3 ratio of 2.79 versus 23.80 in grain-finished beef. Together, the expected fatty acid signature, biological plausibility, and the extremely large effect size observed for MK-4 (Hedges’ g = 6.79) support the possibility that production system is a key determinant of MK-4 levels in beef. Therefore, this work strengthens current understanding of how rearing practices shape the micronutrient composition of livestock products and may have implications for sustainable livestock systems and for human nutrition.