Spatiotemporal dynamics of equine group formation reveal the gradual emergence of social cohesion.

Stable social relationships are essential for horse welfare, yet domestic management often involves regrouping unfamiliar individuals, potentially causing social stress. Fine-scale dynamics of social integration remain poorly quantified due to limitations of observational sampling. Using ultra-wideband real-time positioning, we tracked the development of spatial and social relationships in two newly formed equine groups (n = 19) over 2-12 months. Inter-individual distances decreased significantly, with time spent within 3 m of conspecifics increasing from 1.2 to 27.3% within two months, demonstrating progressive spatial cohesion. Horses introduced with familiar companions integrated more rapidly than those introduced without familiar partners. Agonistic behaviour peaked initially and declined as stability emerged, yet occurred most frequently between closest associates, reflecting either active relationship negotiation or increased interaction opportunity from sustained proximity. No clinically relevant injuries occurred. Affiliative behaviours increased over time and were concentrated among preferred partners. Proximity to hay influenced social interactions, but its effects were context-dependent, varying with resource density, spacing opportunities, and group composition. Network structures initially showed centralisation near feeding areas, later transitioning to more even distribution. These high-resolution data reveal temporal trajectories of equine social integration and underscore welfare recommendations to minimise regrouping, introduce horses with familiar companions, and allow extended stabilisation periods.