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Measurement of serum Total Protein (TP) or Immunoglobulin G (IgG) is frequently used within the dairy industry to monitor failure of passive transfer (FPT) in calves. Through such monitoring, modifications to colostrum handling and feeding techniques can be incorporated into farm practices to improve calf management. Most studies establishing cutoff values of TP or IgG for determination of FPT have been based on data primarily obtained from Holstein calves. The purpose of this study was to determine factors associated with TP and IgG serum concentration in dairy replacement calves. Factors that were studied included, breed (Holstein and Jersey), weight, age, hydration status (packed cell volume) and rectal temperature. A total of 673 calve 1 to 30 days of age were included in the study; 411 Jersey and 262 Holstein calves. Jersey calves had consistently higher TP and IgG serum concentration than Holstein calves. TP concentration was approx. 0.5 g/dL higher, while IgG concentration was more than double that of Holstein calves. This indicates that the cutoff values established for TP (>5.0 mg/dL) and IgG (>1000.0 mg/ dL) in Holstein calves are not appropriate to be used in Jersey calves, needing more research to establish adequate cutoff values for Jersey calves. Another factor strongly associated with both TP and IgG concentration was calf age. Maximum concentrations were achieved at 2-3 days of age. After that, concentrations decreased by approx. 0.07 g/ dL of TP and 74 mg/dL of IgG per day. Our results indicate that there is a narrow window for optimal evaluation of colostrum management in dairy replacement calves, and that different breed of cattle need their own established reference values.