Abstract
The welfare of horses involved in sport and leisure activities has come under increasing scrutiny, both from within the equine sector and from the public. A systematic review of scientific evidence was conducted to derive observable, evidence-based behavioural measures of positive or negative affective state and factors relating to quality of life in the domestic horse (Equus caballus). Two separate searches (including the terms 'emotion/affect', or 'stress') were conducted, with 179 articles being retained. In Part I of this two-part review (companion paper published simultaneously), articles relating to the extent to which the species-specific needs of the horse are fulfilled in the home environment (n = 21), in relation to social grouping (n = 20), and during weaning (n = 14) were reviewed. Experimental tests of affective state in relation to housing and management (n = 8), and studies relating to stereotypical behaviour (n = 7) were also included. Opportunities for behavioural expression were dependent upon the provision of social and physical resources. Withdrawn or agitated behaviours in situ, avoidance behaviour during handling and agonistic intra-species interactions were indicative of negative affective state. Affiliative intra-specific social interactions, and forage ingestion were considered positive signs. For horses to live a good life, their need for space, companionship, and forage must be prioritised from birth and throughout their lives.