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Correlation of Bovine Serum Macroglobulin and Calcium at Parturition

Departments of Biochemistry and Nutrition and of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061
and Biology Division, Oak Ridge National Laboratory, Oak Ridge,Tennessee 37830

ABSTRACT

Serum globulin varied little in cows sampled over a physiological cycle of 1 yr except at parturition and onset of lactation. The 19S macroglobulin peak in parturient cows was elevated 75% shortly before calving with a return to normal (4.8 ± .7% of serum protein) within 18 days after birth. Serum protein remained constant. A drop in serum calcium at birth accompanied the macroglobulin changes from 3.0 mM to 1.9 mM calcium. The elevated 19S macroglobulin component was ₂-macroglobulin by preparative fractionation of macroglobulin samples followed by electrophoresis and by analytical ultracentrifuge studies. Eight cows with parturient hypocalcemia developed the same serum macroglobulin patterns as normal cows during parturition, but serum calcium dropped to .92 mM with inorganic phosphate also decreasing significantly. We isolated, identified, and physically and chemically characterized bovine ₂-macroglobulin to ascertain its function in physiological adjustments to parturition and lactation. Elevated ₂-macroglobulin in parturient or milk fever cows and the diminished serum calcium of these animals were uncorrelated.