Refractometers are the go-to farm tool for checking passive transfer, fast, cheap, and simple, but this study looked at where that method actually falls short. Researchers examined the limitations of using serum total protein or Brix readings to identify failure of passive transfer, questioning how reliable that single number really is. For producers leaning entirely on a refractometer reading to make herd health decisions, this is worth knowing before treating it as the final word.
"Hot topic: Accuracy of refractometry as an indirect method to measure failed transfer of passive immunity in dairy calves fed colostrum replacer and maternal colostrum" — A.J. Lopez, M.A. Steele, M. Nagorske, R. Sargent, D.L. Renaud. J Dairy Sci. 2021;104(2):2032-2039.