Evaluation of serum concentrations of total protein and gamma-globulin as an indicator of serum immunoglobulin G concentration in dairy calves.

The aim of this study was to evaluate precision of estimating serum IgG concentration from total protein (TP) or gamma-globulin (γGLB) concentration as an alternative approach, and to compare morbidity of preweaning dairy calves differing in serum γGLB concentration. In trial 1, blood was sampled from 129 Holstein calves in the first week after birth, and serum concentrations of TP, γGLB, and IgG were measured. Spearman's correlation coefficient (r) between serum IgG and TP concentrations was 0.89, and r between serum IgG and γGLB concentrations was 0.96. Absolute residual (observed - predicted) serum IgG concentrations were smaller when estimated by serum γGLB concentration than by serum TP concentration, and differences in the absolute residuals were smaller for calves fed colostrum replacer (1.68 vs. 4.29 g/L) than those fed whole colostrum (2.41 vs. 3.48 g/L). In trial 2, blood was sampled from 740 Holstein heifer calves during the first week of age, and serum γGLB concentration was measured. The calves were divided into 4 categories based on their serum γGLB concentration; ≥1.0 g/dL (excellent), 0.7 ≤ γGLB <1.0 g/dL (good), 0.4 ≤ γGLB <0.7 g/dL (fair), and <0.4 g/dL (poor). Morbidity for diarrhea and respiratory disease in preweaning dairy calves was determined for the first 28 and 56 d of age, and compared among the 4 categories based on serum γGLB concentration. Calves with serum γGLB concentration higher than 0.7 g/dL (good and excellent) had less diarrhea during the first 28 d of age than those with lower serum γGLB concentration (fair and poor). Calves with serum γGLB concentration higher than 1.0 g/dL (excellent) had less respiratory diseases for the first 56 d of age than those with lower serum γGLB concentration (good, fair, and poor). These results suggest that serum IgG concentration can be estimated more precisely from concentration of γGLB than TP particularly for calves fed colostrum replacer, and that γGLB concentrations in the first week of age are associated with morbidity of calves. Transfer of passive immunity in dairy calves can be assessed effectively by serum γGLB concentration.