The development of equine immunity: Current knowledge on immunology in the young horse.
Authors: Perkins G A, Wagner B
Journal: Equine veterinary journal
Summary
# Editorial Summary: Equine Immune Development in Foals and Young Horses The immune system's maturation from foetal life through to adulthood represents a critical yet incompletely understood period in equine health management. Perkins and Wagner (2015) synthesised current knowledge on how foal immunity develops, revealing that whilst innate immune responses function adequately from birth, adaptive immunity follows a staggered timeline—some antibody responses (IgG1, IgG3, IgG5 and IgA) mature within three months, whilst others (IgG4, IgG7 and IgE) develop gradually throughout the first year, with similar delays observed in T helper cell function. Th1-mediated responses begin shortly after birth but increase slowly over twelve months, whilst Th2 immunity remains virtually absent in the first three months of life, a deficiency that directly correlates with foals' heightened susceptibility to pathogens such as *Rhodococcus equi* and their characteristically poor vaccination responses during early life. This maturation lag explains why traditional vaccination protocols often fail in young stock and underscores the need for evidence-based timing adjustments in preventive medicine strategies. For practitioners involved in foal health, nutrition and performance development, recognising that immune competence and immune maturity are distinctly different concepts should inform management decisions regarding infection prevention, supplementation timing and the realistic expectations for early immunisation programmes.
Read the full abstract on PubMed
Practical Takeaways
- •Young foals are immunologically immature and have reduced responsiveness to traditional vaccines during the first 3 months of life; vaccination timing strategies should account for delayed Th2 immunity development
- •Foals show increased susceptibility to certain pathogens like Rhodococcus equi due to delayed T-cell response development; heightened biosecurity and management protocols are warranted in the first year of life
- •Understanding the maturation timeline of different immune components (antibody types and T-cell responses) can inform prevention strategies and help clinicians establish more appropriate protective protocols for young horses
Key Findings
- •Innate immune responses are functional from birth, but adaptive immune responses are delayed in foals
- •IgG1, IgG3, IgG5 and IgA antibodies mature within 3 months of life, while IgG4, IgG7 and IgE develop slowly over the first year
- •Th2-cell production (IL-4) is almost undetectable in the first 3 months of life, explaining reduced vaccine responsiveness in young horses
- •Th1-cell responses (IFN-γ) begin shortly after birth with gradual increases during the first year, contributing to increased susceptibility to Rhodococcus equi