Population
Population summary is presented in Table 1. On average 60 harness racehorses present each year at the Norwegian University of Life Sciences for HSTE using our standardised protocol. This represents approximately 1080 horses during the study period between 2005 and 2022. Of these, eighteen harness racehorses were diagnosed with compression of the base of the epiglottis during periods of poll flexion and met the inclusion criteria, giving an estimated prevalence rate of 1.7%. Of these eighteen horses, 11 were NSCTs and 7 were STBs. There were 50% (9/18) mares, 39% (7/18) stallions and 11% (2/18) geldings. The horses as a group presented at a mean ± SD age of 4.7 ± 2.0 years. The STBs presented at 4.0 ± 0.8 years (range 3-5 years) and the NSCTs at 5.1 ± 2.4 years (range 3-10 years). The presenting complaint was poor performance alone in 44.4% (8/18), abnormal respiratory noise alone in 33.3% (6/18) and both abnormal respiratory noise and poor performance in 11.1% (2/18). One horse (5.6%) presented due to physical collapse during a race and one horse (5.6%) presented for a routine fitness test. Three horses had abnormal respiratory noise mostly evident when driven on the bit (horse nr. 6, 9 and 15).