Calves are a unique species in how they rely on colostrum ingestion to provide immune protection for the first months of life. Are refractometers an accurate way to quickly and easily measure immune transfer in individual calves?
Adequate colostrum ingestion is the single most important determinant of health, survival, performance and therein profitability in calf’s life. Passive Transfer is commonly used to describe the phenomenon by which a calf acquires its immunity from the dam via colostrum.
My calves received colostrum. How can I now verify that my calves have enough immunity?
Many producers often question if there are visual ways to determine if a calf fails passive transfer; however, it usually requires pulling a blood sample, centrifuging the sample to collect serum and either directly or indirectly measuring the level of IgG.
The indirect way to measure IgG in the serum is by utilizing an optical or digital refractometer which measures serum total protein (STP). This method is considered a calf side test because the blood can be collected on a particular day, centrifuged, and the serum can be placed on the refractometer with the result being known right then. Because serum total protein is readily analyzed and available on the farm, many producers have relied on this test to determine the level of passive transfer in calves. While this has been practiced for many years and it is regarded as a useful tool, the results have frequently been misinterpreted due to limitations of the test.
It is important to understand how a refractometer works and the composition of the serum tested before heavily placing emphasis on data from STP. Believe it or not, refractometers were originally designed for use in the wine, beer and maple syrup industries to measure the amount of sucrose or sugar in water. The refractometer itself, whether it is optical or digital, relies on a light source and prism.
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