Why do horses snort? Researchers in France have found that they appear to be associated with generally positive emotions.
The study team from the University of Rennes 1 said their findings called into question the traditional view of the snort as being mainly for hygiene – clearing the nostrils.
Their findings have linked it to what they describe as a relaxation phase associated with positive emotions of low intensity – what could be termed an ongoing state of good wellbeing.
Mathilde Stomp and her colleagues, writing in the open-access journal PLoS ONE, said the snort is common among perrisodactyls (the mammalian family which includes the horse, tapir, and rhinoceros), and in some species it has been linked to positive contexts.
“We hypothesized that this could be also the case in horses.”
Whinnies, they noted, had been linked to emotions in horses, encoding either their level of arousal or the nature of their emotions.
They said there was a clear need for a thorough description of non-vocal acoustic signals – snorts, snores or blows.
The sound produced through the nostrils during forceful expiration has up to now been mostly considered as having a role in clearing the nostrils of phlegm, flies or other irritants. “However, observations revealed that snorts were produced more in some individuals than in others, without relationship with air conditions.”
The researchers described a study involving 48 horses facing extremes in living conditions, ranging from the restricted conditions of a single stall, with a few hours a day on grass, to a more natural environment, living permanently in stable groups at pasture.
The animals were spread across four sites in Brittany, France.
The riding school horses comprised two populations, 19 at one site and 18 at the other, with different daily management across the two operations. While all were stabled, one population enjoyed one to four hours each day at pasture with variable social partners, while those in the other population went out as groups (from 2 to 11 individuals) on to pasture for about six hours per day every day.
The remaining 11 study animals were kept permanently at pasture, fed hay when necessary, and ridden occasionally for leisure.
The behavioural and postural status of the animals were observed when they snorted. Additionally, the study team evaluated the welfare state of each using recognised welfare indicators.
They found that snort production – there were 560 recorded across the whole study – was significantly associated with situations known to be positive for horses, such as feeding in pasture, and with a positive internal state (ears in a forward or sidewards positions).
The riding school horses produced twice as many snorts when in pasture than in their stall. Indeed, eight horses did not produce any snorts in their stalls.
Further, the horses permanently kept at pasture emitted significantly more snorts than riding school ones in comparable situation.
Horses produced fewer snorts when assessed as being under greater levels of stress, while those assessed with lower stress scores snorted more often.
“Snorts therefore appear as reliable indicators of positive emotions. The more horses emitted snorts, the more they were in a good welfare state,” they said.
In the riding school populations, the horses produced, on average, 5.66 snorts per hour, plus or minus ±3.32. Snort rates clearly differed according to the context of production, with age and sex found to have no bearing.
In total, the study team recorded 454 snorts in the riding school horses: 189 in stall (29 horses) and 265 in pasture (36 horses).
Discussing their findings, the study team said: “It is clear that snorts cannot be merely considered as having a simple hygienic function of clearing the nostrils, expressed during no particular context nor in a specific arousal state.
“Air conditions/dust cannot explain the present results as different horses in the same air conditions could differ in terms of snort production (e.g. correlation with welfare score).”
Snorts, they said, might prove to be a useful indicator of positive emotions.
They proposed that snorts indicated “a relaxation phase associated with positive emotions of low intensity and thus expressed even more by horses in a chronic good welfare state”.
“However, our study does not totally allow to rule out the sanitary function of snort, since dust differences present in stall and pasture contexts have not been examined in detail, but the results show that this is unlikely to explain differences between individual horses.”
The full study team comprised Stomp, Maël Leroux, Marjorie Cellier, Séverine Henry, Alban Lemasson and Martine Hausberger.
Stomp M, Leroux M, Cellier M, Henry S, Lemasson A, Hausberger M (2018) An unexpected acoustic indicator of positive emotions in horses. PLoS ONE 13(7): e0197898. https://doi.org/10.1371/journal.pone.0197898