Testing for failure of passive transfer: are all tests made equal?

Abstract

Testing for failure of passive transfer (FPT) is common practice, yet there is still confusion around the best tests to use. Worldwide, the most common tests used are IgG concentration, total protein (TP) concentration (measured in a laboratory or on a refractometer) and gamma glutamyl transferase (GGT) activity. Of these, IgG concentration is the gold standard but is expensive to test. In a recently published study we compared IgG results with laboratory TP, BRIX refractometer results and laboratory GGT, and concluded that of the three test laboratory TP concentration was the best predictor of IgG uptake and GGT the worst. Using a BRIX refractometer was marginally less accurate than laboratory TP testing but its cost and speed advantages meant that it would still be of significant value when evaluating potential FPT problems on farm. This paper describes the process used to come to these conclusions.