Evaluation of field-based diagnostic methods for assessing passive immune transfer in neonatal lambs

Passive immune transfer (PIT) is crucial for the survival and health of neonatal lambs, and its assessment is vital in early-life management. This study evaluated the effectiveness of three field-based diagnostic methods-analog Brix refractometry, digital Brix refractometry, and immunocrit-for estimating PIT in lambs, using serum total protein concentration as the reference standard. Thirteen lambs born from eutocic deliveries were assessed. The mean serum protein concentration was 7.50 ± 0.70 g/dL, exceeding the 5.0 g/dL threshold for adequate PIT. All alternative methods showed strong positive correlations with serum protein: analog Brix (r = 0.9795), digital Brix (r = 0.9870), and immunocrit (r = 0.8945), with perfect categorical agreement (Kappa = 1.0) across all methods. Analog and digital Brix readings were nearly identical, suggesting consistency between instruments. Although immunocrit showed slightly greater variability, it remained a valid diagnostic tool. A weak correlation was observed between colostrum Brix values and lamb serum protein (r = 0.16; p = 0.6115), indicating that colostrum quality alone does not guarantee successful PIT. Factors such as intake timing, volume, and neonatal vigor likely influence PIT outcomes. These findings support the use of Brix refractometry and immunocrit as reliable, rapid, and cost-effective tools for PIT assessment in lambs under field conditions. Their implementation may enhance early detection of PIT failure, reduce neonatal mortality, and improve flock health and productivity.