Newborn calves must acquire their immunity through the consumption of colostrum. High quality colostrum contains at least 50 mg/mL of Immunoglobulin G (IgG), the primary antibody that protects calves from infection. Colostrum varies considerably in IgG content; therefore, it is critical that producers test colostrum quality before feeding it.
Researchers at the University of Calgary conducted a study to determine which on-farm tool -- the colostrometer or the Brix refractometer -- is better able to determine colostrum quality compared to the laboratory analysis (radial immunodiffusion [RID]) of IgG.
They collected 572 colostrum samples between February and July, 2012 from 14 farms in central Alberta. Herd size ranged from 60 to 300 lactating cows. Samples were analyzed using a colostrometer and Brix refractometer, and results were compared to RID-determined IgG levels. The colostrometer had a greater correlation with RID results, indicating that it is more accurate than the Brix refractometer at predicting true IgG levels. Current literature suggests using 50 mg/mL on the colostrometer and 22o Brix as the cut point for identifying good-quality colostrum, but the results of this study suggest 80 mg/mL and 24o Brix would be better indicators of good quality.
Although the colostrometer is a better predictor of true IgG over a range of IgG values, it is not widely used on farms as it is very fragile, requires a full cup of colostrum, and the results vary with temperature of the colostrum. The Brix refractometer is less fragile, more user-friendly, and uses only 2-3 drops of colostrum. The results of this study showed that the Brix refractometer is most useful when looking at high-quality colostrum. If the colostrum measures 28o Brix or higher, there is a 95% chance that it truly is good quality.
The researchers concluded that the cut points for identifying good-quality colostrum may be different than previous literature suggests. This study also indicates that although the colostrometer is a more accurate tool over a range of IgG levels, the Brix refractometer is useful at confirming truly good-quality colostrum. Overall, using either tool is more beneficial than not measuring colostrum quality at all prior to feeding.