Measuring colostrum quality with a Brix refractometer is a practical method to ensure each calf gets good quality colostrum
IgG is seen as the most reliable indicator of successful transfer of passive immunity to newborn calves. If calves reach a serum IgG level of ≥ 10g/L in a sample obtained between 1 to 7 days after birth, transfer is considered to be successful. To reach this passive immunity level, calves need to be fed at least 3-4 litres of good quality colostrum within 6 hours after birth. Based on the assumption that calves need to receive 100 to 200 g of IgG to ensure they have sufficient immunity against disease, an IgG concentration in cow colostrum of 50 g/L is considered as a cut-off value between good and bad quality colostrum[2,3,4].
A US study on 827 samples in 67 herds showed that almost 30% of colostrum samples had an IgG concentration < 50 g/L. A more recent study carried out in the Netherlands showed similar results: 65% of colostrum samples tested was of good quality, 18% moderate and 17% was of poor quality. It is therefore important for farmers to measure the quality of colostrum they feed to their calves.
The radial immunodiffusion assay (RID), is considered to be the gold standard method for measuring colostral antibodies. Near Infrared spectrometry (NIRS) can be considered as another gold standard test. Neither of these methods can be used routinely on farms[8,9]. Measurement of specific gravity has been proposed as a way to assess colostrum quality but major drawback is the fragility of the colostrometer and the need to clean it between measurements. Color assessment has shown not to be reliable enough.
A hand-held Brix meter can be used to measure the sugar concentration in a few drops of colostrum. The refractive index converted on a Brix scale can be used to distinguish good quality (IgG ≥ 50 g/L) versus poor quality colostrum (IgG < 50 g/L)[9,11,12]. The results of a meta-analysis of 11 studies in which a Brix refractometer was used under practical conditions is presented in this article.
Key takeaways from the research:
Measuring colostrum quality with a Brix refractometer is a practical method to measure levels of colostral antibodies
Colostrum with a Brix value ≥ 22% should be used
Colostrum with a Brix value of < 18% should be discarded
If colostrum has a Brix value of ≥ 18% but < 22%, supplementation should be considered
The results of 11 studies were included in the meta-analysis, resulting in an analysis of 4,251 samples.
Of the total number of colostrum samples the percentage of samples with an IgG level ≥ 50 g/L varied between 67.3% and 92.3%, with a median value of 77.9%, measured by RID (9 studies) or NIRS (2 studies).
If a Brix value of 22% was taken as cut-off point, the sensitivity (ability of the Brix test to identify a sample with IgG ≥ 50g/L as being of good quality) of the Brix test was 80.2% and the specificity (ability of the Brix test to identify a sample with IgG < 50 g/L) was 82.6%. If a Brix value of 18% was taken as the cut-off value, sensitivity increased to 96.1% but specificity decreased to 54.5%. Using this information, it is proposed to use a cut-off value of 22% to select good quality colostrum and to consider storing some of that colostrum as frozen colostrum for other calves. A cut-off value of 18% should be used to discard poor quality colostrum. Colostrum with a value below 18% should therefore not be used. If values are between 18 and 22%, supplementation with colostrum form another dam or with a colostrum product should be considered.
It was concluded that measuring the Brix value with a refractometer is a practical method to test the quality of colostrum on farm. If a value of 22% is taken as cut-off, more than 20% of samples do not have an IgG level of ≥ 50 g/L.
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