The effect of passively acquired antibodies on Lawsonia intracellularis infection and immunity in the horse

AE Page, HF Stills Jr and DW Horohov

It is well understood that equine proliferative enteropathy caused by Lawsonia intracellularis affects weanling horses. The reasons for this have not been documented and a decline in passively acquired antibodies has been hypothesised. This study investigated the effect of the decline in maternal antibodies on the development of clinical or subclinical equine proliferative enteropathy. Four hundred and fifty-three mare and foal pairs from a small area around central Kentucky were enrolled in the study; serum samples were taken within 48 hours of parturition and at monthly intervals thereafter until the foals were yearlings. Antibody status was measured using an enzyme-linked immunosorbent assay (ELISA); disease status was either subclinical (if there were no clinical signs but hypoalbuminaemia was detected) or clinical, if clinical signs were apparent. At the initial post partum sample 44.2% of mares and 38% of foals were seropositive, although a marked variation in farm-specific seroprevalence was noted. During the study period 5.3% and 6.3% of seropositive horses developed clinical or subclinical disease, respectively. There was no effect of maternal antibody status on the development of subclinical or clinical disease. Colts were found to be significantly more likely than fillies to develop clinical disease (odds ratio 5.468) and foals weaned later were at lower risk of developing clinical disease (odds ratio 0.281)

The bottom line: This study shows that passively acquired antibodies to Lawsonia intracellularis to do not have an effect on the development of clinical or subclinical equine proliferative enteropathy, therefore additional factors associated with the weaning period, such as stress, may be the underlying reason for weanling predisposition to the disease.

Photo: Lawsonia Foal


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