Using a hand-held refractometer is an inexpensive, reliable on-farm method to check if you colostrum program is working well.
How well is your colostrum program working? Are you confident that every calf is given 10 percent of their body weight as clean (< 100,000 cfu bacteria), high quality (22+ BRIX) colostrum within four hours of birth? While it can be next to impossible to ensure that all of these important steps happen on a busy farm, every single time a calf is born, there is an easy way to check what calves “say” about the colostrum management on your farm.
Serum total protein (STP) is a reliable on-farm estimate of IgG in the blood in young calves and can be inexpensively checked calf-side or at the vet clinic using a refractometer. Numerous research studies have shown that total protein of 5.2 to 5.5 g/dl indicates that calves have achieved “successful passive transfer” of immunity – that is, a serum IgG concentration ≥10 g/L.
Refractometers are commonly used on farm to measure colostrum quality and work by measuring the way light bends when it passes through a solution. We have learned that a BRIX score of 22 g/dl correlates to colostrum containing at least 50 g/L of IgG. In the same way, total protein predictions or BRIX scores can be used to estimate IgG in the blood of calves using a hand-held refractometer.
Research has shown that in calves less than seven days of age, the majority of proteins circulating in the blood come from colostrum, therefore total protein is a reliable indicator of circulating IgG. There are two scenario’s in which STP is not a reliable indicator and actual IgG must be measured: in calves that were given colostrum replacer and in calves with dehydration.
- In calves fed a colostrum replacer, the ratio of fat to protein and IgG to protein is different than in fresh maternal colostrum, resulting in inaccurate results on a refractometer.
- In calves with dehydration, the blood volume is decreased, resulting in more concentrated protein in the blood, potentially causing false positive readings on a refractometer. A quick way to check hydration levels is to do a skin tent on the neck. If skin does not snap back instantly, the calf has some dehydration. A skin tent that does not snap back within two to three seconds would be a calf that should receive fluids immediately and be checked the following day for serum protein.
To test serum total protein on your farm, work with your veterinarian to learn how to draw blood from the jugular vein in calves one to seven days old. It is important to wait at least 24 hours after first colostrum feeding before blood draw to ensure the colostrum IgG’s have made their way to the blood stream. Collect 2- 5 ml of blood into a clean vacutainer. Either centrifuge the blood for a few minutes, or allow the blood to sit undisturbed at room temperature 12-24 hours until it coagulates leaving plasma at the bottom and serum at the top. With a clean pipette, collect a few drops of the clear serum and place on the refractometer.
Depending on the version of refractometer you are using, read either serum total protein (TP percent) or BRIX. Serum total protein below 5.2 g/dl and BRIX below 8.4 percent is a fail, which correlates to less than 10 g/L serum IgG.
Michigan State University Extension recommends a goal of at least 90 percent of calves one to seven days old testing > 5.2 g/dl; or successful passive transfer of immunity. Those under this standard are said to have Failure of Passive Transfer.
It is a good idea to check calves regularly even when things are going well. Keep records of calves so that over time, you can monitor the success of the colostrum program on your farm. If less than 90 percent of calves are having successful passive transfer, look for the weak link in your system. All calves should receive 10 percent of body weight (generally four quarts) as clean, high quality colostrum within four hours of birth.