Serial investigation of Lawsonia intracellularis seroprevalence and shedding in Thoroughbred foals during the first year

Abstract

Background

There are no studies reporting seroprevalence and faecal shedding of Lawsonia intracellularis (L. intracellaris) in UK foals during their first year of life.

Objectives

To determine seroprevalence and faecal shedding for L. intracellularis in Thoroughbred mares and foals in the United Kingdom. To evaluate associations between clinicopathologic parameters and serology titres in foals.

Study design

Single-centre prospective cohort study.

Methods

Foals from six farms underwent clinical examination, blood sampling for haematology and biochemistry, serum immunoperoxidase monolayer assay (IPMA) for analysis of antibodies against L. intracellularis, and faecal PCR at birth, 3, 6, 9 and 12 months of age. A blood sample was collected from the dams at time point 0 for IPMA analysis.

Results

Forty-seven foals from six different farms were enrolled and 37 completed the entire study. At foaling, 77% (95% CI: 64%–88%) of mares and 64% (95% CI: 50%–77%) of foals were seropositive. There was a positive linear relationship between mare and foal serum titres (rho = 0.723; p < 0.001) and between foal serum titres and immunoglobulin G (IgG) levels (rho = 0.38; p = 0.008). Peak timing for seroconversion occurred between 6 and 9 months of age and between September and January. Only 2 faecal PCR samples tested positive, and no clinical signs of disease were recognised in any foal. Twenty-nine out of 37 foals (78%; 95% CI: 65%–92%) did not seroconvert between 3 and 12 months of age.

Main limitations

Convenience sample encompassing a small number of farms and foals recruited from a single county.

Conclusions

This study suggests frequent exposure to L. intracellularis on UK Thoroughbred stud farms. Peak timing of seroconversion was between 6 and 9 months of age.