Measurement of serum immunoglobulin G (IgG) is used for the assessment of passive transfer of maternal immunity in neonatal crias and foals, with an IgG concentration <10 g/L and <8 g/L respectively, being supportive of failure of transfer of passive immunity (FTPI). Rapid diagnosis of FTPI on the farm allows for the implementation of life-saving treatment to prevent neonatal septicemia in cria and foals and lowers economic loss for camelid and equine breeding operations. The first aim of this prospective study is to assess the accuracy and precision of the stall-side lateral flow IgG assay in serum samples and determine concordance of IgG results in serum and plasma samples for the diagnosis of FTPI in crias. The second aim is to assess accuracy and precision of the stall-side lateral flow IgG assay for the diagnosis of FTPI in serum samples from foals. Blood samples from 50 neonatal cria and 70 neonatal foals will be collected and stored frozen until batch analysis. For accuracy, IgG as measured by the lateral flow IgG assay will be compared to the gold standard automated turbidimetric immunoassay (TIA) with standard method comparison analysis. The TIA assay is configured for automated chemistry analyzers in crias and foals and is in current use for measurement of IgG in these neonates in the Clinical Pathology Laboratory in the Animal Health Diagnostic Center (AHDC). A third, popular commercially available assay will be included in the comparison for foal serum (SNAP Foal IgG assay) as its accuracy and precision has not previously been compared to the TIA. If results are congruent among the assays, then the lateral flow assay offers a better option in foals than the SNAP assay due to its lower cost. For precision, we will determine the interassay coefficient of variation of samples with high, medium, and low IgG concentrations in cria and foal serum analyzed on 10 different days with the lateral flow assay. We already have 28 and 33 serum samples from crias and foals, respectively, in frozen storage for use in the study. These are residual samples remaining after measurement of IgG with the TIA for routine diagnostic purposes and we will continue to obtain additional foal and cria serum samples in this manner. We also have 12 heparinized plasma samples that are paired with serum samples from crias in frozen storage, which were collected with the assistance of our participating private alpaca herd. Serum is the traditional sample for IgG measurement, however plasma is far easier to obtain as the sample does not have to clot before plasma can be separated from cells for analysis. Currently, we do not know if IgG results are equivalent in these two sample types. As a subaim, we will compare IgG concentrations in serum and plasma with the lateral flow and TIA assay in 20 crias to determine if plasma can be used by practitioners and veterinary laboratories alike for IgG measurement. We expect to find that the lateral flow assay will provide similar results to the TIA assay and will be precise, thereby validating its use by practitioners to assess crias and foals for FTPIs tall-side. We expect to find that it will provide similar results in foals to the currently used SNAP foal IgG, giving practitioners a cheaper choice for selecting a stall-side for assessing for FTPI. We also expect that plasma and serum IgG results will be comparable in crias, thus expanding the sample type practitioners can use to test for FTPI.