Neutrophil functions and serum IgG in growing foals.
Authors: Demmers S, Johannisson A, Gröndahl G, Jensen-Waern M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Neutrophil Functions and Serum IgG in Growing Foals Passive immunity in foals wanes significantly during the first weeks of life, creating a critical window of vulnerability to infection, yet the maturation timeline of active immune defences remains poorly characterised. Demmers and colleagues tracked neutrophil phagocytosis, oxidative burst capacity, and CD18 expression in six Standardbred foals from 2 to 56 days old and monthly thereafter to 8 months, comparing results against healthy mature horses and using flow cytometry, chemiluminescence, and radial immunodiffusion to measure immune competence. Phagocytic function remained significantly impaired until 3 weeks of age when autologous serum was used as an opsonin, whilst killing capacity—assessed via oxidative burst—was initially depressed but reached or exceeded adult levels by 3 months; serum IgG fell from 10 g/l at 2 days to a nadir of 5 g/l at 2 months before gradually recovering to 10 g/l by 8 months. These findings illuminate why foals experience heightened bacterial infection risk during the first 3–8 weeks of life: they lack both adequate passive antibody coverage and functionally mature innate immune responses during this critical developmental window. For practitioners managing young foals, this evidence underscores the importance of maintaining strict biosecurity and monitoring protocols during the pre-weaning period and supports judicious use of prophylactic strategies during this immunologically vulnerable phase.
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Practical Takeaways
- •Foals have significantly compromised immune function during their first 3 weeks of life; heightened vigilance for early signs of infection is warranted during this critical window
- •Passive immunity from maternal IgG wanes by 2 months—monitor foals closely during this transition period before active immunity is fully established
- •Young foals (especially <3 months) are at highest risk of bacterial infection due to combined deficits in neutrophil killing capacity and serum IgG levels
Key Findings
- •Neutrophil phagocytic ability was impaired until 3 weeks of age when using autologous serum as opsonin
- •Killing capacity (oxidative burst) was low initially but reached or exceeded mature horse levels by 3 months of age
- •Serum IgG declined from 10 g/L at 2 days to 5 g/L at 2 months, then gradually recovered to 10 g/L by 8 months
- •Impaired neutrophil function and declining IgG in early foalhood may explain increased susceptibility to bacterial infections during this period