Refractometry as a measure of the immunoglobulin status of the newborn dairy calf: comparison with the zinc sulfate turbidity test and single radial immunodiffusion.

Immunoglobulins were quantitated by single radial immunodiffusion in 34 female Holstein-Friesian calves which had been kept with their dams for the first 24 hours of life. The mean immunoglobulin G1 (IgG1) concentration was 1.063 g/dl; IgG2, 0.093 g/dl; IgM, 0.171 g/dl; and IgA, 0.125 g/dl. Both serum total protein as measured by refractometer and zinc sulfate turbidity measured at 498 nm gave good correlations with total protein, which were significant, P less than 0.001. Plasma total protein had a slightly poorer correlation with total immunoglobulins, presumably due to variable fibrinogen content. Plasma total protein gave a better correlation with total immunoglobulins than did any of the immunoglobulin classes individually. Total protein by refractometer underestimated naturally occurring or added immunoglobulins by one-third.