Brix Refractometer to Measure Immunity in Calves
We have another research report on the use of Brix refractometry to measure immunity in female dairy calves. If you do not care to read any farther just remember the number 8.4 to indicate passive transfer failure.
The report, "Deelen, S.M. and others, "Evaluation of a Brix Refractometer to estimate serum immunoglobulin G concentration in neonatal dairy calves," Journal of Dairy Science 97:3838-3844 June 2014," is summarized by the authors:
"Brix refractometer measurements were highly correlated with serum IgG. A value of <8.4% most accurately predicted FTP [failure of passive transfer], providing a reasonable estimate of serum IgG concentrations in the majority of the calves tested." (page 3843)
The one reservation the authors point out is that their study population of calves was from well-managed dairies that had low rates of passive transfer failure (about 5 percent). From a practical point of view I doubt that this bias invalidates their recommendation to use 8.4% as the threshold for passive transfer failure. This number was over 94% accurate in identifying positive calves (adequate immunity similar to 5.5 BSTP). It did misclassify some calves as positive that were actually failures - at the BSTP level of 5.2 about 5% of negatives (below 5.2) were misclassified as okay.
Overall, pretty accurate for an on-farm super quick test. My recommendation now is to purchase a unit that can be used to test both colostrum and blood serum using Brix scales.