Equine Failure of Passive Transfer Study Guide

Overview and Clinical Importance

Failure of Passive Transfer (FPT) is the most common immunodeficiency disorder in horses, occurring in 3-24% of newborn foals. Due to the epitheliochorial nature of the equine placenta, no immunoglobulin transfer occurs in utero, making foals entirely dependent on colostral antibody absorption for early immune protection. FPT is defined as inadequate transfer of maternal immunoglobulins (primarily IgG) from colostrum to the foal's bloodstream, resulting in increased susceptibility to life-threatening infections including septicemia, pneumonia, and septic arthritis.

FPT represents a critical NAVLE topic because early recognition and treatment dramatically improves survival rates. Understanding the pathophysiology, diagnostic testing, and treatment protocols is essential for any equine practitioner managing neonatal foals.

Pathophysiology of Passive Transfer

Equine Placentation and Immunoglobulin Transfer

The mare has an epitheliochorial placenta with six tissue layers separating maternal and fetal blood. This prevents transplacental transfer of immunoglobulins, making foals born agammaglobulinemic (essentially no circulating antibodies). While there is minimal IgM production in utero, this is insufficient for protection against environmental pathogens.