Evaluation of the optical refractometer for lamb serum immunoglobulin estimation

Resistance of lambs to neonatal diseases has been shown to be related to their serum immunoglobulin levels. These may be estimated in the laboratory by the zinc sulphate turbidity test (ZSTT). An experiment was designed to evaluate the optical refractometer, a relatively simple and inexpensive piece of equipment which measures the refractive index of a serum sample and thus provides an estimate of its total protein content. Refractometer readings of neonatal lamb sera were found to be closely correlated to their ZSTT readings (r = 0.89). The refractometer appears eminently suited to farm use avoiding elaborate and time consuming laboratory procedures. The limitations of the tests are discussed.