Horse sports face public scrutiny, particularly regarding concerns about horse welfare. Understanding how the physical positioning of the horse's head and neck while being ridden affects behavior is crucial for improving welfare standards. This study aimed to investigate the influence of head–neck position (HNP) in ridden horses–specifically, the vertical and poll angles–on conflict behavior (CB). Furthermore, it aimed to identify a critical threshold at which HNP significantly affects behavioral outcomes. Elite dressage horses were observed during warm-ups and tests at competitions, and horses presented in educational videos were analyzed to examine the relationship between HNP and CB. A total of 191 rides were analyzed, HNP parameters (angle to the vertical of nasal plane, poll angle, and shoulder angle) and CB indicators (e.g., unusual oral behaviors and tail swishing) were recorded over 3-minute intervals using Observer XT (Noldus). Data were analyzed using general linear mixed-effects models, with CB (sum of all behaviors) as the response variable and horse-rider-ID as a random effect. Both poll and vertical angles had significant negative effects on CB, indicating that horses exhibited more CB when these angles decreased (p < 0.001, df = 139.64/137.28, respectively). Shoulder angle also had a significant impact on CB in one model (p = 0.014, df = 136.61). A vertical angle of -7.5° behind the vertical was identified as the cut-off value associated with an increase in CB. Stallions exhibited more CB than mares and geldings (p < 0.001, df = 73.16). The models demonstrated good fit, with consistently non-significant effects of age, breed, and bit type. Optimizing HNP during riding is crucial for enhancing behavioral well-being and the overall welfare of dressage horses in competitive settings.
