Could Adults be Used to Improve Social Skills of Young Horses, Equus caballus? Marie Bourjade Maı ¨c Moulinot Se ´verine Henry Marie-Annick Richard-Yris Martine Hausberger UMR CNRS 6552 Ethologie-Evolution- Ecologie, Universite ´ de Rennes 1 Avenue du Ge ´ne ´ral Leclerc Campus de Beaulieu F-35042 Rennes Cedex, France E-mail: marie.bourjade@univ-rennes1.fr ABSTRACT: We investigated the effects of the introduction of foreign adults on the behavior of young horses. First, we observed the behavior of 1- and 2-year-old domestic horses housed in same-age and same-sex groups (a standard housing system, but different from a natural situation). Then, two same-sex adults were introduced into each experimental group. Observations made before, during and after an introduction indicated that young horses reared in homogeneous groups of young had different behaviors compared to other domestic horses reared under more socially natural conditions. After the introduction of adults, young horses expressed new behaviors, preferential social associations emerged, positive social behavior increased and agonistic interactions decreased. These results have important implications both for understanding the influence that adults may have on the behavior of young horses, and in terms of husbandry, indicating the importance of keeping young horses with adults, although further studies are still necessary. ß 2008 Wiley Periodicals, Inc. Dev Psychobiol 50: 408–417, 2008. Keywords: horse; social influence; young–adult interaction; social development INTRODUCTION Young animals receive social influence from their conspecifics and are able to learn from them: develop- mental trajectories result in recurring social interactions among group members (Hinde, 1983; West, King, & White, 2003; White, King, Cole, & West, 2002b). Social context, partly determined by the social structure of a species, refers to the quality and number of individuals young can interact with (age, sex, relatedness...) or to the duration of their association. Such a social context can affect learning opportunities and therefore shape the young’s behavior (Berman, Rasmussen, & Suomi, 1997; White et al., 2002b). Mothers provide the first social influence young mammals receive (Berman et al., 1997; Holmes & Mateo, 1998; Kendrick, Haupt, Hinton, Broad, & Skinner, 2001). However, the presence of siblings or conspecifics of the opposite sex can affect social preferences (e.g., Belding ground squirrels, Spermophilus beldingi: Holmes & Mateo, 1998; domestic horses: Khalil & Kaseda, 1998) or social behavior (e.g., social play in female kittens, Felis catus: Caro, 1981; aggressiveness in mice, Mus musculus: Korpela & Sandnabba, 1994). Similarly, other adult group members can influence sexual development, maturation, or development of aggressive- ness (e.g., musk shrews, Suncus murinus: Rissman, Taymans, & Wayne, 1990; guinea pigs, Cavia porcellus: Sachser & Lick, 1991; mice: Sandnabba, 1993; elephants, Loxodonta africana: Slotow, van Dyk, Poole, Page, & Klocke, 2000; golden hamsters, Mesocricetus auratus: Delville, David, Taravosh-Lahn, & Wommack, 2003). Social enrichment experiments with captive, domestic, or wild animals showed mainly that the presence of conspecifics enhanced success in coping with future social challenges (Pietropaolo et al., 2004; Schapiro, Bloomsmith, Porter, & Suarez, 1996). For example, young rhesus monkeys, Macaca mulatta, housed in pairs or in groups developed more species-specific behavioral patterns in comparison to isolated individuals (Schapiro et al., 1996). In elephants, older bull control young males by decreasing their aggressiveness and suppressing their Received 22 February 2007; Accepted 8 January 2008 Correspondence to: M. Bourjade Contract grant sponsor: COST (‘‘Haras Nationaux’’) Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/dev.20301 ß 2008 Wiley Periodicals, Inc.