Equine IgG / Passive Immunization (Foals)

Why Foals Need Colostrum

Foals are born immunologically naive and with virtually no circulating antibodies of their own. The mare’s diffuse epitheliochorial placenta prevents the transfer of maternal immunoglobulins to the unborn foal. The protection of the newborn foal during the first weeks of life therefore relies exclusively on the intake of immunoglobulins—primarily immunoglobulin G (IgG)—from colostrum (first milk). Healthy foals begin suckling within the first one to two hours; maternal antibodies are detectable in the blood after just a few hours.

Insufficient Passive Immune Transfer (FPT)

The absorption of intact immunoglobulins through the intestinal epithelium is only possible during the first few hours of life and declines rapidly; with so-called intestinal closure (gut closure) occurring within about 24 hours, the ability to absorb these substances largely ceases, so that oral administration of colostrum thereafter is of little benefit. If colostrum is ingested too late, in insufficient quantities, or of inadequate quality, or if absorption is impaired, this results in insufficient passive immune transfer (Failure of Passive Transfer, FPT). FPT is the most common immune system disorder in foals; contributing factors include premature milk let-down in the mare, poor-quality colostrum, inadequate suckling, and prematurity.

Consequences for the foal

Failure of passive transfer does not itself cause any distinct symptoms, but it is a major risk factor for the foal’s health: Affected animals are significantly more susceptible to infections, particularly neonatal sepsis (septicemia), which is one of the leading causes of illness and death in the first weeks of life. Adequate transfer is a prerequisite, but no guarantee, that a foal will remain healthy.

IgG Test for Foals

The success of passive transfer in foals can be assessed by measuring the serum immunoglobulin G (IgG) concentration, typically about 18 to 24 hours after birth; foals at risk may be tested earlier. As a reference, a serum IgG concentration above 800 mg/dl is considered sufficient, a value between 400 and 800 mg/dl indicates partial failure, and a value below 400 mg/dl indicates complete failure of passive transfer. An early assessment of IgG status allows for targeted corrective measures, such as supplemental colostrum administration within the absorption window or intravenous plasma administration after the window has closed.

Rapid Test Component

The Fassisi® Equine IgG enables a semiquantitative assessment of immunoglobulin G status in foals using serum or whole blood, thereby supporting bedside evaluation of passive immune transfer.

References can be found here.