Abstract
Failed transfer of passive immunity (FTPI) has been used to predict pre-weaning disease in beef calves. However, FTPI has a wide range of reported sensitivities and specificities; therefore, the diagnostic value of testing for FTPI to predict a beef calf’s disease risk is questionable. Our objective was to determine the positive and negative predictive value of FTPI classification on pre-weaning morbidity in beef calves using a Bayesian latent class analysis. Pre-weaning health records and IgG concentrations from 1,569 beef calves across 3 populations were used. Calves were classified as having FTPI using 7 IgG cut-off values (500, 800, 1,000, 1,200, 1,600, 1,800 and 2,400 mg/ dL). A Bayesian latent class model assuming conditional independence between the IgG concentrations and morbidity diagnosis was used to obtain estimates of the test sensitivity, specificity and positive and negative predictive value for the IgG cut-off values using informed priors; estimated herd cumulative incidence of morbidity ranged from 3.5% to 26.1%. Immunoglobulin G had a median (95% credible interval) sensitivity ranging from 28% (22%, 36%) for 500 mg/dL to 47% (40%, 55%) for 2,400 mg/dL and a median (95% credible interval) specificity ranging from 98% (95%, 100%) for 500 mg/dL to 64% (62%, 67%) for 2,400 mg/dL. Testing for FTPI performed the best in herds with a high cumulative incidence of morbidity (> 15%). In herds with low cumulative incidence of morbidity, testing for FTPI did not aid in the detection of calves that would develop pre-weaning morbidity.
Published Version
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