Colostral immunoglobulin G as a predictor for serum immunoglobulin G concentration in dairy calves

Feeding newborn calves high-quality colostrum is of well-recognised importance as calves that do not receive an adequate concentration of immunoglobulin-G (IgG) have an increased risk of morbidity and mortality. This experiment aimed to characterise IgG concentrations in colostrum from the first milking in New Zealand dairy cows, examine IgG status of calves, and to evaluate the use of a refractometer for estimating quality of colostrum in terms of IgG concentration. Heifer calves entered the calf shed at 0-24 hours of age and were fed pooled first-milking colostrum within eight hours of entering the shed. Blood samples were taken the following morning. Cows were individually milked and samples from individual and pooled colostrum were analysed. IgG concentration of serum and colostrum samples were determined by turbidimetric immunoassay. IgG concentration was adequate according to commercial reference ranges in 70.1% of individual colostrum, 80.0% of pooled colostrum and 82.5% of calf serum samples. There was no relationship between calf serum and IgG concentration in dam or pooled colostrum. The refractometer was a good predictor of IgG concentration in serum (r=0.64, P<0.0001) and colostrum both in dam (r=0.87, P<0.0001) and pooled (r=0.81, P<0.0001) samples. The relationship between IgG concentration and refractometer reading indicates that it could be a useful on-farm tool.