Use of serum total protein as a proxy for passive transfer status in lambs

BACKGROUND: Serum total protein (TP) is commonly used to investigate failure of passive transfer of immunity (FPTI) in cattle. This short communication explores the use of serum TP as a proxy of passive transfer (PT) status in lambs. METHODS: Blood samples were obtained from 434 lambs within 8‒24 hours of birth to measure serum immunoglobulin G (IgG) and TP. The relationship between serum IgG and TP was described using a linear regression model. Receiver operating characteristic analysis was used to select a serum TP cut-off for sub-optimal PT. The serum TP cut-off with the optimal sensitivity (86.8%, 95% confidence interval [CI]: 80.8‒92.1%) and specificity (80.2%, 95% CI: 75.3‒84.8%) to detect serum IgG concentrations of 24 mg/mL or less was 6.8 g/dL. LIMITATIONS: This work involved lowland lambs sampled from a single well-managed farm. Further work is needed to establish FPTI cut-offs in a variety of sheep populations. CONCLUSIONS: Serum TP measurement is an appropriate field diagnostic to estimate the PT status of lambs in lowland flocks.