Simple SummaryThe impact of various degrees of poll hyperflexion on the welfare of ridden horses has previously been evaluated. The International Society for Equitation Science advised that lesser degrees of poll flexion should also be investigated. The aim of this study was to evaluate the effects of two degrees of poll flexion with a difference of only 15° on the respiratory system and behaviour of a horse during ridden exercise. Twenty high-level dressage and twenty show-jumping horses were ridden twice for 40 min 3 weeks apart, with the first ridden exercise at an 85° ground angle and the second at a 100° ground angle (the angle between the ground and the line from the forehead to the muzzle). Conflict behaviour was registered, as were manifestations of upper airway collapse, observed on an over-ground endoscopy. Arterial blood oxygen and lactate, pleural pressure, pharyngeal diameter, and heart and respiratory rates were evaluated. For both groups, at 100°, both conflict behaviours and upper airway abnormalities were seen more frequently, the intrathoracic pressure was higher, and the pharyngeal diameter was lower. At 85°, relaxation behaviours were more frequent. Compared to the first ridden exercise, the HR and RR were lower at the beginning of the second ridden exercise but higher at the end. The differences found here support the idea that an increase of just 15° in ridden poll flexion can have negative effects on the respiratory system and behaviour of a horse and therefore on its welfare.AbstractFrom previous studies, the International Society for Equitation Science has advised that further research be conducted on the physiological/psychological effects of less-exacerbated poll flexion angles. We aimed to evaluate the effects of two riding poll flexion positions with a difference of only 15° on the respiratory systems and behaviour of horses through an evaluation of dynamic airway collapse via over-ground endoscopy, the pharyngeal diameter, pleural pressure, arterial oxygenation and lactate, HR/RR, and the occurrence of conflict behaviours. Twenty high-level dressage and twenty show-jumping horses underwent a 40 min ridden test at a ground angle of 85°; 3 weeks later, they underwent a ridden test at a 100° ground angle (the angle between the ground and the line from the forehead to the muzzle) and in a cross-over design. Using a mixed model for repeated measures, Wilcoxon/Friedman tests were carried out according to the experimental design and/or error normality. For both groups, at 100°, conflict behaviours and upper airway tract abnormalities were significantly more frequent, and the pleural pressure was higher, and the pharyngeal diameter was lower. At 85°, relaxation behaviours were significantly more frequent. Lactate was significantly higher at 100° only in the dressage horses. Compared to the first test at 85°, the HR/RR were significantly lower at the beginning of the second test (at 100°) but higher at the end. The significant differences identified in these dressage and show-jumping horses support the idea that an increase of just 15° in riding poll flexion can have negative effects on the respiratory system and behaviour of a horse and therefore on its welfare.