The Stud Book Returns of racehorse breeders to Weatherbys Group Ltd. in 2003 recorded 16,008 live foals in England, Scotland, Wales, the Irish Republic and Northern Ireland; the same organization estimates the U.K. racehorse population to be 40,000 (Defra, 2004). The link between diminished equine well-being and social isolation (where physical segregation from conspecifics is regarded as preventing the expression of instinctive social behaviour) is well documented (e.g. Fraser, 1992, ). The negative consequences of social deprivation during the primary socialization period have been studied in adult equines; these include fear responses when presented with novel stimuli, generalized fear-induced aggression and stereotypic behaviours (Fraser, 1992, ; McGreevy et al., 1995b, . The manifestation of ‘a normal behavioural repertoire’ is widely viewed as an indication of well-being (Hurnik et al., 1985, ). The acquisition of typical equine behaviour occurs in a socialization period that involves close contact with conspecifics (e.g. identification through olfactory investigation and reciprocal maintenance behaviours such as allo-grooming).