Straight from the horse's mouth: Changes in salivary oxytocin, cortisol and behaviour in horses interacting with unfamiliar humans

Human-horse interactions can have positive outcomes for humans, but not much is known about their effects on horses. As horses are increasingly used for equine-assisted interactions and many horses interact with unfamiliar humans on a daily basis, there is a need to study how interactions with unfamiliar humans affect horses. Salivary oxytocin and cortisol in combination with behavioural parameters are useful for assessing the effects of human-horse interactions on equine stress and welfare. This study investigated the effects of 10 min of standardized, affiliative interactions with two unfamiliar humans on salivary cortisol and oxytocin concentrations in 18 riding school horses related to their behaviour. Interactions were limited between 10:00–15:00 to avoid circadian effects. Pre- and post-interaction saliva samples were taken from the humans and the horses before and immediately after the interactions with an average sample interval of 20.7 ± 0.6 min and concentrations were determined through ELISA. Behavioural parameters included standing in voluntary proximity, receiving physical contact, nose touching, sniffing in relation to oxytocin and locomotion, chewing, licking, and head shaking related to cortisol. In humans, descriptive statistics indicated that the salivary oxytocin and cortisol concentrations were similar pre- and post interaction. In horses, a linear mixed model showed no significant differences in salivary oxytocin and cortisol concentrations when comparing pre- and post-interaction samples. Salivary oxytocin in horses was not significantly affected by voluntary proximity, receiving physical contact, nose touching, sniffing. Salivary cortisol in horses was negatively affected by headshaking and tended to be positively affected by lip licking. These results do not indicate that affiliative interactions with unfamiliar humans negatively affect stress and eventually welfare in horses, in this particular population under the context studied.