Study validates stall-side IgG assay for foal passive transfer checks: full analysis

A newly published Equine Veterinary Journal study adds fresh evidence for a stall-side option in one of equine neonatology’s most time-sensitive decisions: whether a foal has received enough maternal antibody. The paper validates the Sidekick lateral-flow IgG assay as a point-of-care test for measuring foal immunoglobulin G, reporting strong agreement with gold-standard laboratory methods and good repeatability, with the goal of helping clinicians act faster when failure of passive transfer is suspected. The article was published online April 28, 2026. (pure.ulster.ac.uk)

That matters because passive transfer remains a core early-life checkpoint in foal care. Foals depend on colostrum-derived immunoglobulins after birth, and inadequate transfer is associated with increased susceptibility to infection and sepsis. Standard laboratory methods such as radial immunodiffusion and immunoturbidimetric assays are well established, but they require sample handling, transport, and turnaround time that may not fit the pace of on-farm decision-making. Clinical references commonly define complete failure of passive transfer at less than 800 mg/dL at 18 to 24 hours in some settings, while treatment-oriented categories often distinguish severe failure below 200 mg/dL, partial failure at 200–800 mg/dL, and adequate transfer above 800 mg/dL. (pure.ulster.ac.uk)

In the new study, investigators assessed the Sidekick test using serially diluted foal samples spanning 0.8–20 g/L, with three replicates, and compared results against radial immunodiffusion and immunoturbidimetric testing. They also used serum and plasma samples from 10 foals to create cohorts representing successful and failed passive transfer, and they checked agreement between matched whole-blood and plasma samples in three foals. Reported recovery across the clinically relevant 4–8 g/L range was 96.3% to 109.5%, with coefficients of variation from 3.7 to 10, which the authors described as excellent recovery and high repeatability. They concluded that the assay could reduce delays tied to processing, transport, and reporting, and help inform whether to start or continue treatment for a foal with failure of passive transfer. (pure.ulster.ac.uk)

The broader industry context helps explain the interest. Point-of-care and field-friendly IgG testing in foals is not new, and equine clinicians have long used a mix of direct and indirect methods, including commercial stall-side assays and refractometry-based estimates. But the tradeoff has often been convenience versus precision. Prior literature and clinical teaching materials continue to emphasize that direct IgG measurement is the more reliable approach, while total protein or refractometer-based screening can be less dependable in some neonatal settings. Sidekick’s own product materials position the assay as a real-time option for foals at elevated risk of failure of passive transfer and say it was designed for use when waiting on a laboratory result may delay care. (sciencedirect.com)

I didn’t find substantial independent expert commentary on this specific paper yet, which isn’t unusual given how recently it was published. Still, the paper’s framing aligns with long-standing clinical priorities in equine neonatal medicine: test early enough to preserve treatment options, and use results to guide colostrum supplementation, plasma administration, or closer monitoring. Educational and reference sources continue to recommend IgG assessment in the first day of life, especially when nursing, colostrum quality, dystocia, maternal illness, or sepsis risk raise concern. (ivis.org)

Why it matters: For veterinary professionals, this is less about a brand-new clinical concept than about workflow. If a quantitative stall-side assay can reliably mirror lab-based IgG testing, it could tighten the timeline between blood draw and treatment, reduce uncertainty in ambulatory practice, and support clearer conversations with pet parents and breeding clients during the narrow passive-transfer window. It may be especially useful in farms or practices where laboratory access is limited after hours or on weekends. At the same time, the study’s small sample size means practices will likely want to see larger independent datasets before treating the assay as a full replacement for established laboratory methods in all cases. (pure.ulster.ac.uk)

What to watch: The next step is likely external validation in larger, more diverse foal populations, along with real-world data on how stall-side quantitative IgG testing changes treatment timing, plasma use, outcomes, and cost in breeding-season practice. (pure.ulster.ac.uk)