Immunity of Foals: What Is Normal IgG?

Foals are born with an intact, though low-functioning, immune system. Because there is no transfer of immunoglobulins, including immunoglobulin G (IgG), from mares to their fetuses in the uterus, foals depend on antibodies they acquire from colostrum to fend off pathogenic assaults. In fact, the immune status of foals can be gauged by measuring the amount of IgG in serum, but at what age are IgG levels at their peak?

A group of Australian researchers tracked IgG levels of healthy foals from birth to weaning*. Blood samples were collected from all 35 foals immediately after birth but before nursing and then at 12 hours, 24 hours, 7 days, 15 days, 21 days, 28 days, 56 days, 84 days, 112 days, and 140 days of age. Blood was taken from the jugular vein and centrifuged, and the plasma was removed and frozen for later analysis. IgG concentrations in plasma were determined by the radial immunodiffusion test for equine IgG.

As expected, IgG was highest collectively for the group of foals at 12 hours (4,129 mg/dl), and IgG gradually decreased as the foals matured until they reached 56 days of age, at which time levels fluctuated a bit.

“Well-nourished mares in good health typically produce sufficient antibody-rich colostrum for their newborn foals,” said Catherine Whitehouse, M.S., a nutrition advisor at Kentucky Equine Research. “To support high-quality colostrum production and optimal passive transfer of antibodies, mares can be supplemented with a marine-derived source of omega-3 fatty acids, the most noteworthy of which are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). This would be especially prudent for mares that are known to produce poor-quality colostrum.”

The importance of offering a marine-derived source of omega-3s should be underscored, according to Whitehouse.

“Long-chain omega-3s, like DHA and EPA, from a marine-derived source are used more efficiently as precursors to local hormones than short-chain omega-3s, such as those found in flax or other plant products. By using a product rich in DHA and EPA, you’re one step ahead of other omega-3 supplements,” she explained.

The use of products containing omega-3 fatty acids on breeding farms has amplified recently, not just because of their usefulness in boosting immunity, but also due to their benefits to stallions, particularly those used in artificial-insemination programs.

Be sure to choose an omega-3 product that is made entirely from marine sources, such as EO-3, and not one blended with plant-based ingredients.

*Kang, H.S., K. Jackson, and A.J. Cawdell-Smith. 2018. IgG levels in healthy foals from birth through weaning. In: Proc. Australasian Equine Science Symposium 7:37.