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 a calf’s life. Passive Transfer is commonly used to describe the phenomenon by which a calf acquires its immunity from the dam via colostrum.
Serum total protein (STP) is an indirect measure of IgG levels. While measuring IgG directly is the gold standard, it is expensive and slow. Refractometers offer a practical on-farm alternative.
Brix refractometers are reliable for measuring IgG in both colostrum and serum. Research shows a strong correlation between Brix percentages and actual IgG concentrations.
Test healthy calves between 24 hours and 7 days of age. A threshold of 8.4% Brix or 5.2 g/dL STP is used as a benchmark for successful passive transfer.
“...the correct way to utilize this test is on a population level and to answer one question: Is my colostrum management program likely working or not working?”
Some colostrum replacer products may result in lower STP readings compared to natural colostrum, potentially leading to a false diagnosis of failure of passive transfer (FPT).