Evaluation of 3 assays for failure of passive transfer in calves.

This study examined the sensitivity, specificity, predictive values, and classification accuracy of 3 commonly used screening tests for failure of passive transfer: the sodium sulfite turbidity test, the zinc sulfate turbidity test, and refractometry relative to serum immunoglobulin G1 (IgG1) concentrations determined by radial immunodiffusion. Serum samples were obtained from 242 calves ranging from 1 to 8 days of age. Using a serum concentration of 1,000 mg/dL IgG1, to define adequate passive transfer, the zinc sulfate test had a sensitivity of 1.00 and a specificity of 0.52 in the detection of inadequate passive transfer. The endpoint of the test appeared to be higher than desired; calves testing negative had mean serum IgG1 concentration of 955 mg/dL and a large proportion of calves with adequate passive transfer were misclassified as positive for failure of passive transfer. Using the qualitative zinc sulfate test, the percentage of calves correctly classified with regard to passive transfer status was less than that observed with either the sodium sulfite test or refractometry. The sensitivity of the sodium sulfite assay was 0.85 at a 1+ endpoint and 1.00 at a 2 or 3+ endpoint. The specificity of the sodium sulfite assay varied from 0.87 at a 1+ endpoint and 0.56 at a 2+ endpoint. The sensitivity and specificity of refractometry varied from 0.01 to 1.00 depending on the choice of endpoint. Refractometry correctly classified the largest proportion of calves with regard to their passive transfer status at test endpoints of 5.0 and 5.5 g/dL, 83% and 82% respectively. The highest percentages of calves correctly classified occurred with the sodium sulfite test using a 1+ endpoint (86.30%) and refractometry using a 5.0 g/dL endpoint (83.00%). A regression equation was developed that permitted calculation of an optimal endpoint for refractometric determinations of total serum protein concentration. A serum protein concentration of 5.2 g/dL was equivalent to 1,000 mg/dL serum IgG1. Optimal selection of tests for passive transfer status in calves will be governed by the prevalence of failure of passive transfer, test performance, and the anticipated costs of classification errors.

Prediction of calf mortality by use of tests for passive transfer of colostral immunoglobulin.

OBJECTIVE: To examine the ability of several commonly used tests for evaluation of passive transfer of immunoglobulin to predict mortality in dairy replacement heifers. DESIGN: Prospective observational study. ANIMALS: 246 dairy replacement heifers between 1 and 8 days of age. PROCEDURE: Using serum samples obtained from each calf, total serum protein concentration and results of zinc sulfate turbidity, sodium sulfite turbidity, radial immunodiffusion, and glutaraldehyde coagulation were determined. Calves were monitored for 100 days, and relative risks for death were calculated. Logistic regression models predicting death also were developed. RESULTS: None of the logistic regression models detected a significant association between test results and mortality. The greatest relative risks of mortality were observed in calves with serum protein concentrations < 4.5 g/dl, serum IgG1 concentrations < 500 mg/dl, and sodium sulfite test scores < 1+. CLINICAL IMPLICATIONS: Calves with lower passive transfer values had increased risk of death; however, failure of passive transfer is not an infallible predictor of mortality.

Evaluation of a whole blood glutaraldehyde coagulation test for the detection of failure of passive transfer in calves.

The accuracy of a commercially available whole blood glutaraldehyde clot test in the detection of failure of passive transfer (serum immunoglobulin [Ig]G1 < 1,000 mg/dL) in neonatal calves was evaluated. Serum samples were obtained from 242 calves ranging in age from 1 to 8 days, and comparisons were made with serum IgG1 concentrations determined by radial immunodiffusion. Both the sensitivity and specificity of the currently marketed whole blood glutaraldehyde clot test are inadequate for routine diagnostic use. Concerns regarding test sensitivity are the most problematic. Sensitivity varied from 0.41 to 0.00, depending on the choice of test endpoint. Specificity varied from 0.85 to 1.00, depending on the choice of test endpoint. Regression analysis demonstrated that the relationship between serum IgG1 concentration and the glutaraldehyde clot results, although significant (P < .10), was of negligible biological relevance (r2 = .034).