The effect of passively acquired antibodies on Lawsonia intracellularis infection and immunity in the horse.
Authors: Page A E, Stills H F, Horohov D W
Journal: Equine veterinary journal
Summary
# Editorial Summary Equine proliferative enteropathy (EPE), caused by *Lawsonia intracellularis*, typically affects young horses, though the underlying mechanisms remain incompletely understood; one longstanding hypothesis suggested that declining maternal antibodies predisposed foals to infection. Page *et al.* prospectively followed 369 Thoroughbred mare–foal pairs across 15 Kentucky farms over 13 months, measuring *L. intracellularis*-specific antibodies via ELISA from birth through the yearling year to determine whether passive immunity influenced disease susceptibility. Contrary to expectation, passive antibody status had no protective effect: approximately 5.3% of seropositive foals developed clinical EPE and 6.3% subclinical infection, with no significant difference between those with high versus low maternal antibody titres. Sex and weaning timing emerged as stronger risk factors, with colts showing over five times greater odds of clinical EPE than fillies (OR 5.468), whilst foals weaned in September or later demonstrated substantially reduced risk (OR 0.281). These findings suggest that age-related susceptibility to EPE cannot be attributed simply to antibody waning, redirecting investigation towards sex-hormone influences, microbial exposure timing, and potential environmental or management factors that correlate with weaning season—insights that warrant further study to better inform preventative strategies on farms experiencing EPE.
Read the full abstract on PubMed
Practical Takeaways
- •Passive immunity from mares does not protect foals against L. intracellularis infection; other age-related factors may explain susceptibility patterns
- •Colt foals warrant closer monitoring for EPE signs compared to fillies, suggesting sex-based biological differences in disease susceptibility
- •Weaning timing (September or later) may be protective; earlier weaning may increase EPE risk, potentially through stress or management factors
Key Findings
- •Passively acquired antibodies to L. intracellularis had no protective effect against clinical or subclinical EPE, with 5.3% and 6.3% of seropositive horses developing clinical or subclinical disease respectively
- •Colts were significantly more susceptible than fillies to presumptive clinical EPE (OR 5.468, P=0.034) and combined clinical/subclinical EPE (OR 3.861, P=0.006)
- •Foals weaned in September or later showed lower risk of developing presumptive EPE (OR 0.281, P=0.05)
- •Study challenges the hypothesis that age-based susceptibility to EPE is explained by declining maternal antibodies