Investigation of Metabolites and Mineral Content in Blood Serum of Dairy Cows of the Simmental Breed in Samsun Province During the Transition Period

This study evaluated the metabolic and mineral profiles in the blood serum of Simmental dairy cows during the transition period to assess their energy, protein, and mineral status. A total of 78 cows from 10 farms in Samsun Province were grouped based on farm size (medium, large), altitude (sea level, mid-altitude), and dietary energy level (low, optimum). Blood samples were collected three weeks before calving, at calving, and three weeks postpartum. Farm size and altitude had no significant effect on serum glucose and NEFA levels; however, dietary energy levels had a significant impact (P = 0.004). Cows fed optimum energy diets had significantly higher prepartum serum glucose concentrations (P < 0.008). NEFA and BHBA levels remained below risk thresholds, indicating no severe negative energy balance. Postpartum, serum total cholesterol and HDL levels increased significantly (P < 0.001), while LDL levels remained stable, reflecting mild liver stress and effective NEFA utilization. LDL levels were higher in cows on low-energy diets (P < 0.001), but without adverse hepatic effects. Total protein levels were lowest prepartum and increased postpartum, particularly in cows fed optimum energy content. Liver enzymes (AST and ALT) were influenced by both feed and period but remained within normal physiological limits. Triglyceride levels remained within reference ranges, suggesting no hepatic fat accumulation. Altitude had a significant effect on MDA levels, which were elevated at mid-altitudes. In contrast, SOD levels showed no significant variation. Serum calcium and magnesium were influenced by dietary energy levels, while phosphorus levels remained unaffected. In conclusion, both dietary energy level and physiological period significantly influenced metabolic and mineral parameters in Simmental dairy cows during the transition period. Conversely, farm size and altitude had minimal effects. Feeding cows an optimal-energy diet supported overall metabolic health throughout the transition period.