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First UK study identifies peak risk period for Lawsonia seroconversion in foals   THE UK’s first seroprevalence study of Lawsonia intracellularis in foals has identified the age at which they are most likely to be exposed to the bacterium, helping stud farms determine the optimal time for vaccination. Vets from Rossdales Equine Hospital , in collaboration with the VetPartners Clinical Board Support Team, conducted the study into Lawsonia intracellularis , the bacterium responsible for equine proliferative enteropathy (EPE). The bacterium can cause sporadic disease in foals, but until now, it has been unclear how frequently foals in the UK are exposed to it. Caroline Ribonnet and Emily Floyd, both RCVS Recognised Specialists in Equine Internal Medicine, and Vicky Colgate, a veterinary researcher with an MSc in Veterinary Epidemiology and Public Health, all from the world-renowned Rossdales Equine Hospital in Exning, near Newmarket, collaborated to determine antibodies to, and faecal shedding of, Lawsonia Intracellularis in foals from UK Thoroughbred Stud farms.     A total of 47 foals from six farms were enrolled and monitored from birth, with testing carried out every three months until 12 months of age. Complete data was obtained for 37 foals. The main objective of the study was to determine the seroprevalence of L. intracellularis in mares and in foals during the first year of life on Thoroughbred stud farms in the UK. As well as the timing of seroconversion in foals, the research team were also interested in identifying any clinical signs, changes in clinicopathologic parameters and evidence of faecal shedding associated with L. intracellularis. Findings from the study revealed that at timepoint 0 (parturition), 77% of mares and 64% of foals were seropositive, indicating significant colostral transfer of maternal antibodies to the foals. Over the course of the study, 75% of foals seroconverted, meaning they became seropositive following a previous negative test, indicating exposure to the bacterium following loss of maternal antibodies. Only 22% (8 out of 37) of foals that completed the study did not seroconvert, and at least one seroconversion event was recorded on every participating farm. The research also identified a clear peak period of exposure: most seroconversions occurred between six and nine months of age, particularly between September and January, the autumn and winter period. As the samples were taken before vaccination against Lawsonia intracellularis became widespread in the UK, the findings provide valuable insight to guide vaccination strategies on UK Thoroughbred stud farms. With the vaccine requiring administration 30 days prior to anticipated disease, the study’s results suggest that vaccination protocols should be commenced before the peak epidemiological exposure period of autumn/winter, and before 6-9 months of age. Additionally, the study provides comparative seroprevalence data against which future studies could explore the effect of introducing routine vaccination protocols. The initial concept for the study came from Rossdales Clinical Director Emily Floyd, who works within their Neonatal Intensive Care Unit. Funding for the project was obtained from the Horserace Betting Levy Board (HBLB) Small Project Research Grant 2014 and the Thoroughbred Breeders Association (TBA). Natalie Robinson, from VetPartners’ Clinical Board Support Team (CBST), joined the research to support with statistical analysis. The CBST has both clinical and extensive research experience and empower VetPartners clinical teams to undertake clinical quality improvement and research.  Vicky said: “This study has helped us identify when foals on UK stud farms are most likely to encounter Lawsonia intracellularis for the first time. The results suggest that exposure most commonly occurs between six and nine months of age, after maternal immunity has declined, which provides valuable information when considering vaccination strategies. By understanding this risk period more clearly, breeders and veterinarians can make more informed decisions about protecting youngstock from this potentially serious disease.” Caroline added: “As the first UK study to investigate the seroprevalence and timing of Lawsonia intracellularis exposure in foals, these findings provide an important foundation for future research. The work improves our understanding of how widely the bacterium is present on stud farms and offers evidence that can help guide both disease surveillance and preventative healthcare strategies in the years ahead.” Read the study here: https://doi.org/10.1111/eve.70115 Bio details: Caroline Ribonnet MVetMed, DipECEIM, MRCVS is an RCVS Recognised Specialist in Equine Internal Medicine and a Diplomate of the European College of Equine Internal Medicine (ECEIM). After graduating from Ghent University in 2016, she completed an internship in equine medicine and surgery before undertaking a residency in Equine Internal Medicine in Belgium, achieving Diplomate status in 2023. Caroline joined Rossdales Equine Hospital as a medicine clinician. Between two maternity cover periods at Rossdales, she spent a year as head of internal medicine at Via Nova Equine Services in Belgium, focusing on equine sports medicine. During her time at Rossdales, she was first author of a study investigating the prevalence of Lawsonia intracellularis infection in the UK equine population, conducted in collaboration with Rossdales and VetPartners. Caroline is currently a medicine clinician at Bell Equine Veterinary Clinic in Kent. Dr. Victoria A. Colgate MA VetMB MSc MRCVS qualified from the University of Cambridge in 2014. After graduating she completed a Clinical Training Scholarship at the Cambridge Equine Hospital before working in a busy polo practice in Ascot. She joined Rossdales Equine Hospital in June 2017 as the Margaret Giffen Resident in Clinical Research, where in addition to carrying out research projects she attained an MSc in Veterinary Epidemiology and Public Health. After time away in a specialist role as a Veterinary Epidemiologist at Equine Infectious Disease Surveillance (EIDS), Vicky returned to Rossdales in July 2023 as a Research Associate, a role kindly funded by the Margaret Giffen Charitable Trust. She has a strong interest in the care and welfare of sports horses and drives forward the practice's application of evidence-based medicine through implementation of clinic-based research and production of associated publications. Emily F. Floyd BVSc, DipACVIM, CertAVP (Veterinary Dermatology), MRCVS is an RCVS Recognised Specialist in Equine Medicine (Internal Medicine) and Diplomate of the American College of Veterinary Internal Medicine. Emily is a member of the internal medicine  team at Rossdales Equine Hospital and has a particular interest in equine neonatology . She joined Rossdales in 2009 and became a partner in April 2016 and a clinical director in 2021. Emily’s main role is working within the Neonatal Intensive Care Unit , in addition to working within the internal medicine department. In 2012, she became an RCVS Specialist in Equine Medicine (Internal Medicine), having been awarded recognised specialist status by the Royal College of Veterinary Surgeons (RCVS). She is also a Diplomate of the American College of Veterinary Internal Medicine, which she achieved during 3 years at the University of California’s Veterinary Medical Teaching Hospital at Davis prior to joining Rossdales. She has completed a number of research projects related to neonatal foal conditions and has published and lectured widely on the subject. Emily also has a keen interest in veterinary dermatology and in 2025 she was awarded the Certificate in Advanced Veterinary Practice in Veterinary Dermatology.