Applied Animal Behaviour Science 126 (2010) 37–44 Contents lists available at ScienceDirect Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim Discrimination between conspecific odour samples in the horse (Equus caballus) Becky Hothersall a,∗ , Patricia Harris b , Lotta Sörtoft c , Christine J. Nicol a a Animal Welfare & Behaviour Group, Department of Clinical Veterinary Science, University of Bristol, Langford, North Somerset BS40 5DU, UK b WALTHAM Centre for Pet Nutrition, Freeby Lane, Waltham-on-the-Wolds, Melton Mowbray, Leicestershire LE14 4RT, UK c Hartpury College, Hartpury, Gloucestershire GL19 3BE, UK article info Article history: Accepted 11 May 2010 Available online 8 June 2010 Keywords: Horse Olfaction Social discrimination Urine Faeces abstract Behavioural observations suggest that smell is important in social discriminations between horses but balanced studies of this capacity are lacking. We used a habituation–discrimination procedure to investigate the ability of horses to distinguish between pairs of odour samples from different individuals. In Study 1, separate tests were conducted for urine, faeces or fleece fabric previously rubbed on the coat (to pick up body odour samples (BOS)) and donor pairs differed in sex, and age. 10 pregnant mares each underwent three tests, one per sample type. A test consisted of three successive 2-min pre- sentations of a sample from Individual A with a simultaneous presentation of a sample from Individual B during the final presentation. Doubly repeated measures ANOVA indicated a main effect of sample type on investigative response (df = 2, f = 7.98, P = 0.004): durations were longer for BOS than for urine or faeces but habituation across trials was most consis- tent for urine. In the final presentation, mares demonstrated discrimination by investigating the novel urine sample (B) more than the repeated sample (novel: median 8.0 s, IQR = 10; repeated: median 2.5 s, IQR = 6; z = -2.558, P = 0.008). In Study 2, urine samples from cas- trated male donors were used and neither mares nor their 4-month-old foals discriminated between samples from different individuals in the final presentation. The findings suggest that urine odour may contain some information that horses can use to discriminate between conspecifics. This may be limited to the level of broad categories such as sex or reproduc- tive status; further investigation is needed to reveal what functional information can be transmitted and what compounds are involved. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The ability of animals to discriminate between con- specifics confers obvious benefits. Differentiation between kin and non-kin helps avoid inbreeding, identifying own- from other-group members helps herd members to co- ordinate their movements, and knowledge of another ∗ Corresponding author at: Animal Welfare & Behaviour Group, Divi- sion of Clinical Veterinary Science, University of Bristol, Langford, North Somerset BS40 5DU, UK. Tel.: +44 117 331 9062. E-mail address: b.hothersall@bristol.ac.uk (B. Hothersall). individual’s age, sex or dominance status allows an animal to modify its behaviour appropriately (Heitor and Vicente, 2007). Recognition at the individual level permits further adjustment of animals’ responses in light of their previous experience of one another, including the outcome of ago- nistic or co-operative interactions. These benefits are appli- cable to domesticated or captive animals as well as those living in the wild. It is important to understand how and to what extent farmed and companion animals discriminate between conspecifics because welfare can be compromised if living conditions disrupt animals’ normal mechanisms for discrimination, breaking down stable social structures and increasing aggression (Mendl et al., 2002). 0168-1591/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.applanim.2010.05.002