The Way to a Man’s Heart Is through His Stomach: What about Horses? Carol Sankey 1 *, Se ´ verine Henry 1 , Aleksandra Go ´ recka-Bruzda 2 , Marie-Annick Richard-Yris 1 , Martine Hausberger 1 1 Ethologie Animale et Humaine, Universite ´ Rennes1/UMR-CNRS6552, Station Biologique, Paimpont, France, 2 Polish Academy of Sciences, Institute of Genetics and Animal Breeding, Jastrze ˛biec, Wo ´ lka-Kosowska, Poland Abstract Background: How do we bond to one another? While in some species, like humans, physical contact plays a role in the process of attachment, it has been suggested that tactile contact’s value may greatly differ according to the species considered. Nevertheless, grooming is often considered as a pleasurable experience for domestic animals, even though scientific data is lacking. On another hand, food seems to be involved in the creation of most relationships in a variety of species. Methodology/Principal Findings: In this study, we used the horse training context to test the effects of food versus grooming during repeated human-horse interactions. The results reveal that food certainly holds a key role in the attachment process, while tactile contact was here clearly insufficient for bonding to occur. Conclusion/Significance: This study raises important questions on the way tactile contact is perceived, and shows that large inter-species differences are to be expected. Citation: Sankey C, Henry S, Go ´ recka-Bruzda A, Richard-Yris M-A, Hausberger M (2010) The Way to a Man’s Heart Is through His Stomach: What about Horses? PLoS ONE 5(11): e15446. doi:10.1371/journal.pone.0015446 Editor: Georges Chapouthier, Universite ´ Pierre et Marie Curie, France Received August 13, 2010; Accepted September 21, 2010; Published November 15, 2010 Copyright: ß 2010 Sankey et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funding was provided by Comite ´ d’Orientation Scientifique et Technique (COST, Les Haras Nationaux, http://www.haras-nationaux.fr/portail/) and Re ´gion Bretagne (http://www.bretagne.fr/internet/jcms/j_6/accueil). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: carol.sankey@univ-rennes1.fr Introduction How do we bond to each other? What is it that leads to the process of attachment? In psychology, bonding is defined as the process of development of a close, interpersonal relationship [1]. Bonding typically refers to the process of attachment that develops between romantic partners, close friends or parents and children, but has also been used for human-animal relationships [2]. There is evidence that oxytocin and vasopressin hormones are involved in the bonding process and in other forms of prosocial and reproductive behaviour [3]. Of all bonds, the maternal (mother-infant) bond is one of the strongest, in which suckling (i.e. breastfeeding in humans) has been reported to have a fostering role [4,5]. Animal research has shown that the endocrine response to suckling (oxytocin release) plays an essential role in maternal bonding by promoting maternal care-giving behavior [6]. Thus one of the strongest bonds in the animal kingdom is, at least partly, a feeding bond. Interestingly, the detachment in the feeding bond goes together with a detachment in the affectionate bond [7]. More generally, food sharing has been described as a reciprocal act of physical affiliation [8] and an essential component for the development of pair bond [9]. Food calls are another example of how food holds a prime position in the formation and maintenance of close relationships [10]. Don’t we also say that little gifts keep friendship warm? Is there a better little gift than a box of sweets or chocolates to make a lover’s heart melt or fill a grandmother with joy? However, inter-individual bonding is often described in terms of social interactions and physical contacts. For this may well reflect real bonding in some species (e.g. in humans: [11], in cats: [12]), the value of tactile contact may differ according to the species considered. The same questioning arises when considering human-animal relationships. Even though it is clear that the taming process can be achieved by positive association condition- ing: humans being the providers of food and water for domestic animals, they become secondarily associated with those positive stimuli [13], many still use diverse forms of tactile contact (e.g. stroking, grooming) to initiate bonding. While for the domestic dog, the human presence itself may be rewarding [13], more precocial species seem to have a less positive perception of human contact [14]. Nevertheless, grooming is often believed to be and used as a primary reinforcement, partly because it has been shown to induce a decrease in the groomee’s heart rate [15,16]. Here, we investigated whether grooming could be used to promote bonding and facilitate learning, by comparing it to a food-reward that has proven efficient for both [17,18]. Materials and Methods Experiments complied with the current French and Polish laws related to animal experimentation and were in accordance to the European directive 86/609/CEE. This experiment only included PLoS ONE | www.plosone.org 1 November 2010 | Volume 5 | Issue 11 | e15446