Foals are born without any immune protection. | iStockBecause foals are born without any immune protection, failure of adequate antibody transfer through nursing leaves them vulnerable to life-threatening infections. Veterinarians must therefore confirm IgG levels shortly after birth and determine if intervention is needed. Brody Ann Klinglesmith, MS, DVM, resident veterinarian at Bar E North Breeding and Performance Horses, in Kiowa, Colorado, reviewed methods of measuring IgG levels in newborn foals during her presentation at the 2025 American Association of Equine Practitioners Convention, held Dec. 6-10, in Denver, Colorado.Klinglesmith explained that the equine fetus develops within an epitheliochorial placenta (where the outer membrane of the fetus contacts the maternal uterine lining), which means antibodies do not cross from mare to foal before birth. Newborn foals must ingest colostrum within the first 12-24 hours of life to absorb maternal antibodies through the gastrointestinal tract. Veterinarians measure immunoglobulin G (IgG), the most prevalent of all the colostrum components and the focus of diagnostics for clinicians, to determine whether this process, called passive transfer, has occurred.Testing IgG Levels in Newborn FoalsMeasuring IgG in the post-suckling foal can help ascertain the quality of antibody absorption and predict his immune systems ability to protect him from infections, lameness, septicemia (the presence of bacteria or bacterial toxins in the bloodstream), and death, Klinglesmith said. We want all veterinarians, especially ambulatory veterinarians who may be the first on scene to those foals, to be able to get really good, quantitative numbers in order to truly treat those foals in the best way possible, she added.She and her team looked at four different devices that determine efficacy of colostral antibody passive transfer in foals. They evaluated the testing options available based on:Ease of useRate of resultPortabilityAffordabilityKlinglesmith said the gold standard for checking IgG in foals is the single radial immunodiffusion test (SRID, a quantitative method that measures the concentration of antibodies or antigens), but it takes 24 hours and is not accessible to the ambulatory practitioner. Most veterinarians prefer the animal reproduction systems (ARS) densimeter (density meter), she added. There is also the SNAP foal IgG device, a semiquantitative test that estimates the amount of IgG in the sample. Finally, she said the Immuno-Check G by TargetVet is a 10-minute test that is simple to use and gives quick, reliable results for the ambulatory veterinarian.Evaluating IgG Testing Methods in HorsesTo see how the three testing methods compared to the gold standard, Klinglesmith and her colleagues collected blood samples from 18 neonates two, four, six and 12 hours post-suckling to see how the antibody numbers changed and numbers compared across devices.When looking at the TargetVet values against the ARS densimeter and gold standard SRID, they found comparable results. The SNAP test being semiquantitative did make direct comparisons a bit difficult, but there were significant differences between the SNAP test (and the other tests), especially at the two- and 12-hour time points, Klinglesmith said. Having true quantitative results is very valuable when managing foals that youre treating in order to determine if interventions are working or if you need to add some interventions.Take-Home MessageMeasuring IgG in newborn foals quickly and accurately is vital to determining the success of passive transfer and evaluating their health. Ambulatory veterinarians often evaluate foals first, so they need diagnostic tools that are accurate, easy, and reliable to use. Klinglesmith and her team found that the TargetVet and ARS densimeter were both comparable to the gold-standard SRID. We found that when it came to portability and accessibility, the TargetVet device was significantly better for ambulatory practices, she said.