Evaluation of variation in serum globulin concentrations in dairy cattle

Background: Several factors may influence the concentration of serum globulins in healthy cows and thereby affect clinical interpretation; however, few studies have addressed sources of variation in globulin values. Objectives: The purpose of this study was to compare colorimetry-based total serum globulin values with electrophoretically-determined serum globulin fractions and with TgG concentration, and to evaluate diurnal and long-term physiological variation and the effects of lactation and venipuncture site on serum globulin concentrations in Holstein dairy cattle. Methods: Serum total globulin and albumin concentrations were analyzed by colorimetry and electrophoresis in 86 lactating cows; IgG concentrations were determined by radial immunodiffusion in 41 dry and 34 lactating cows. Serum globulins were analyzed hourly for 24 hours in 8 lactating cows and weekly for 15 weeks in 6 additional cows. Globulin concentrations were compared in samples obtained from jugular and coccygeal venipuncture sites in 4 cows. Results were analyzed using parametric statistical tests. Results: Colorimetry-based total serum globulin concentrations correlated well with gamma-globulin fractions (r(2) = 0.87) and IgG concentrations (r(2) = 0.91). Diurnal variation of total serum globulins concentration was significant (P.01); however, globulins did not vary significantly over a 15-week period. Mean serum globulins concentration in samples obtained from the jugular vein was 2.35 g/L higher than that in samples obtained by coccygeal venipuncture (P <.0001). Conclusions: The colorimetric method used widely in routine laboratory analyses remains a useful test for globulins determination in dairy cattle. However, time of sampling and venipuncture site should be considered in the interpretation of serum globulins on serial or interindividual specimens. (C) 2004 American Society for Veterinary Clinical Pathology.