In a previous Michigan State University Extension article, Did that calf get enough good quality colostrum?, we discussed research recently conducted on using a Brix Refractometer to assess failure of passive transfer (FPT). The refractometer is used to check serum from calves, and can, therefore, provide valuable monitoring of a farm’s colostrum program.
The first step is to purchase a Brix Refractometer. There are many models available and most seem to work very well. One basic requirement is that it reads from zero up to approximately 25 percent brix so you can use it for both colostrum and FPT determination. Other features to consider are size, whether or not it has a shield to block out light and general ruggedness of the machine. Cost ranges from $200 to $500.
However, after you purchase your refractometer, you will also need additional supplies and some training. Necessary supplies include: blood tube holders (or syringes) and 20-gauge one-inch needles, blood sample tubes to hold the sample for clotting, a centrifuge (optional) and small disposable pipettes for collection of the serum from the blood tubes.
Dairy producers should work with their veterinarian to gain experience in collecting blood samples from the calf’s jugular vein. Your veterinarian can also recommend specific blood collection supplies. Blood samples should be drawn from calves between 36 and 60 hours after birth.
Once the sample is collected in the tube, clotting should occur in about five to 60 minutes depending on the type of tube used and type of clot activator present in the tube. Without a centrifuge, samples will need to sit for 24 hours prior to retrieving the serum sample. A small table top centrifuge can be purchased for under $200 and will speed the separation of serum more quickly. No matter by which method the serum is separated, draw off a small amount of clear serum from the blood tube using the small pipette and place two or three drops on the Brix Refractometer for reading.
By definition, FPT has occurred when total serum protein is below 5.2 – 5.5 g/dL or total serum IgG is below 10 mg/mL. A recent Washington State University College of Vet Medicine study evaluated use of the Brix Refractometer to determine FPT and correlated the Brix percentage reading with serum IgG levels. From the study, they determined that a Brix reading of 8.3 percent equated to an Immunoglobulin G (IgG) of 10 mg/mL. Producers collecting serum samples from calves should therefore be looking to achieve at least an 8.3 percent Brix reading.