Combined effects of chelated minerals and chromium as a nutritional intervention strategy for high-oxidative stress transition cows

Abstract The transition period in dairy cattle represents a critical physiological window where oxidative stress (OS), insulin resistance (IR), and systemic inflammation often converge, predisposing animals to subclinical ketosis (SCK) and significant production losses. Although the benefits of individual trace elements are well-documented, the synergistic potential of a chelated mineral mixture (CMM) and chromium (Cr) as a targeted "rescue strategy" for cows pre-screened for high OS remains under-investigated. This study evaluated the combined effects of a CMM and organic Cr as a targeted nutritional intervention strategy for transition dairy cows pre-screened for high OS. Thirty-six multiparous Holstein cows were assigned to four cohorts ( n = 9 each): Negative Control (NEG; low OS), Positive Control (POS; high OS), CMM, and CMM/Cr, supplemented from T − 28 to T + 28 . Blood samples were collected at five time points relative to each animal’s calving date: T -28 , T -14 , T 0 (calving), T +14 , T +28 . Serum was harvested and stored at –20°C for subsequent biochemical analysis. Daily milk yield was recorded, and milk aliquots (10 mL) were collected at T +14 , T +28 for composition analysis and somatic cell counting (SCC). Un-supplemented POS cows exhibited severe redox imbalance, an exaggerated postpartum insulin nadir, hyper-lipolysis [elevated non-esterified fatty acids (NEFA) and β- hydroxybutyrate ( β -HBA); P < 0.05], and elevated serum amyloid A (SAA; P < 0.05]. Significant Treatment x Time interactions ( P < 0.05) occurred across key biomarkers. The combined CMM/Cr intervention restored redox homeostasis, significantly decreasing reactive oxygen species and the Oxidative Stress index (OSi; P < 0.05). At T + 28 , serum SOD activity in CMM/Cr cows was significantly lower than all other cohorts ( P < 0.05), reflecting reduced demand for superoxide scavenging following redox resolution. CMM/Cr stabilized insulin concentrations, improved insulin sensitivity (RQUICKI; P < 0.05), and attenuated NEFA and β -HBA surges ( P < 0.05). Furthermore, CMM/Cr suppressed SAA ( P < 0.05), whereas postpartum haptoglobin levels were maintained higher in CMM and CMM/Cr cows than in POS controls ( P < 0.05). CMM/Cr significantly attenuated SCC dynamics ( P < 0.05). Milk yield and composition represented non-significant numerical trajectories ( P > 0.05). OSi correlated inversely with milk yield ( r = -0.74, P < 0.05) and positively with NEFA, β -HBA, and SAA ( P < 0.05). This study demonstrates that combined CMM and Cr supplementation provides as an effective nutritional intervention strategy to mitigate systemic OS and metabolic dysregulation in transition cows while maintaining overall production output.