Hemoconcentration differs in neonatal dairy calves: Considerations for assessment of transfer of passive immunity

[Display omitted] •Calves showed individual variability in the degree of hemoconcentration.•Adjusting total protein increased the proportion of calves with poor and fair TPI.•Variability in hemoconcentration should be considered when assessing TPI. Assessing transfer of passive immunity (TPI) is a critical management strategy to evaluate colostrum management and feeding; however, variability in hemoconcentration or serum or plasma volume in calves might influence TPI assessment. The objectives of this study were to (1) describe the variability in hemoconcentration as well as TPI in Holstein calves in New York State and (2) describe the effect of adjusting total protein (TP) for the degree of hemoconcentration by applying a sample average proportion of plasma in blood (PP) on TPI assessment. Records of TP and PP from 703 Holstein calves 1 to 9 d of age from 19 commercial dairy farms were analyzed. The PP was determined by centrifugation of microhematocrit tubes and serum and plasma TP was determined by digital refractometry. Transfer of passive immunity was categorized using unadjusted TP (uTP) as excellent = ≥6.2, good = 5.8–6.1, fair = 5.1–5.7, and poor