Infection caused by Kingella kingae is an emerging infection in young children. A novel bacterial species was identified by MALDI-TOF as Kingella kingae in synovial and bone tissues surgically debrided from thoroughbred horses aged between 3 and 15 months with osteo-articular infection.  Subsequently we investigated serological responses. We tested serum samples from three separate herds by indirect immunofluorescence antibody test (LED-IFAT) using a pathogenic isolate K. kingae and novel equine species K. equi sp nov.as substrates. Equines in Farm A showed no evidence of antibodies to Kingella and therefore served as control. Seropositivity was detected in equines in Farm B (5/10 tested) and Farm C (1/9 tested). In Farm B 1/5 seropositives demonstrated seroconversion on paired sera. Based on this preliminary study, it is possible to detect by LED-IFAT antibodies to a previously unidentified equine pathogen and this assay may be of value in screening herds to determine seroprevalence and seroconversion rates for this novel pathogen.