The objective of this study was to compare the serum mineral concentrations of blood taken from jugular, mammary, and coccygeal veins. Eighty-seven Holstein– Friesian cows and heifers were used to determine serum concentrations of calcium (Ca), inorganic phosphorus (IP), and magnesium (Mg). Cows were bled from three and heifers from two veins at one occasion. The studied cows were consisted of high production dairy cows, dry cows, and heifers. Statistical analysis of these serum biochemical values was evaluated with analysis of variance test. Serum Ca concentrations of mammary vein were significantly lower than jugular vein in all groups (P=0.0033) and high production cows (P=0.0002). Serum IP concentrations of jugular vein in all groups were significantly lower than IP serum concentrations of coccygeal vein (P=0.0001) and mammary vein (P=0.0026). Comparison of different groups defined that serum IP concentrations of jugular vein in high production cows (P=0.0019) and heifers (P=0.0088) were significantly lower than coccygeal vein. In addition, serum IP concentrations of jugular vein in dry cows were significantly lower than coccygeal (P=0.0077) and mammary veins (P=0.0061). Statistical analysis did not reveal any significant difference between serum Mg concentrations of different veins in all or each groups (P>0.05). Introduction With the development of automated laboratory instrumentation, the use of certain blood parameters as indicators of the physiological, nutritional, metabolic, and clinical status of farm animals is gaining a wider application. In addition, methodology and reagents are becoming more standardized with the use of commercially available diagnostic kits (Doornenbal et al. 1988). For the evaluation of clinical tests in veterinary laboratories, a reference basis of normal values of clinically healthy farm animals is essential. It is well known that variables such as breed, stage of growth, age, reproductive status, and stage of lactation have an influence on many blood parameters (Radostits et al. 2007). The objective of the present study was to compare three venipuncture sites (jugular vein, coccygeal vein, and mammary vein) on the serum calcium (Ca), inorganic phosphorus (IP), and magnesium (Mg) concentrations in three groups of high production dairy cows, dry cows, and heifers.

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