Snorting and chewing helps horses calm down when they are stressed

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He sees a tree stump, and you roll your eyes… because you know what’s coming next. This is the part where your horse plants his feet, perks up his ears, snorts, blows, and chews his own saliva. If you said he’s stressed at that moment, you’d be right. That’s especially true because of the snorting and non-nutritive chewing, as revealed in a new study. But what you might not know is why he acts that way. Not why, as in what’s so terrifying about a tree stump. But rather, why do horses perform certain behaviours when they’re stressed?

According to Italian scientists, snorting and chewing in the face of stress are ‘resilience’ behaviours; that is, behaviours that help horses cope and recover more quickly after a stressful event. Stress causes significant hormonal changes designed to give them more energy (to escape or defend themselves from danger), but above all else, their body just wants to get back to the normal state of calm it was enjoying before the stressful moment. This state which is the opposite of stress, is called ‘homeostasis’.

Horses (like other animals and people) become ‘resilient’ to stress by displaying behaviours that help them return to a state of homeostasis. In essence, certain behaviours that look ‘stressful’ actually help alleviate stress.

Snorting and what scientists call non-nutritive chewing seem to be effective towards that goal in horses, said Chiara Scopa, PhD, of the Italian National Reference Centre for Animal Assisted Interventions at the Istituto Zooproflattico Sperimentale delle Venezie in Legnaro, Italy. Often overlooked, snorting and chewing can help clue horse people in to the fact that their horse is stressed—which isn’t always as obvious as it might seem.

“It’s crucial to recognize specific stress-related behaviours in horses, but there’s actually still very little that’s known about these behaviours,” Scopa said during her presentation at the 2018 conference of the International Society for Equestrian Science, held in Rome, Italy.

“When riders and caretakers identify these signs, they can properly interpret the internal state of their animals and improve their welfare accordingly,” she said.

In their study, Scopa and her fellow researchers exposed 33 horses to a balloon that suddenly appeared in their stalls. The scientists recorded cardiac rates – heart rate and heart rate variability, which have already been associated with states of stress – as well as behaviour.

They found that, of all the behaviours the horses performed, only two seemed to be related to resilience. Horses showed remarkable changes in their rates of chewing and especially snorting – the harsh, quick, loud respiratory sound (not to be confused with the rumbling snort that horses often make when grazing) right after seeing the balloon. And those changes were significantly associated with evolving patterns of heart rate variability, suggesting that the behaviours were helping to bring the horses’ nervous systems back to a state of homeostasis.

‘Resilience’ sounds like an exciting term related to individual horses’ ability to withstand the pressures of stress better than others. But in this context, it’s a scientific term that refers to horses’ ability in general to find stress-coping behaviours. As such, the study doesn’t yield hope for being able to test horses for their ‘resilience’, according to Paolo Baragli, PhD, of the Department of Veterinary Sciences in the University of Pisa, in Italy. And unfortunately, resilience probably isn’t linked to any particular kind of personality or temperament.

However, knowledge of resilience can be a huge step forward in ensuring better horse management and welfare, Baragli said.

“For owners and riders, it should be mandatory to know when their horses show calming behaviours (meaning that horses are experiencing stressing/arousal conditions),” he said. “Most of the behaviours that are typically described as a sign of stress or frustration during riding are not validated by physiological parameters, and therefore, we can’t be sure about their connection to stress.”

The fact that the new study highlights two behaviours – snorting and non-nutritive chewing – however, can now be eye-openers. “A main finding of this study is that non-nutritive chewing is actually not a behaviour indicating a relaxed state, as a lot of people believe, but rather indicates that the horse is trying to relax himself because he’s in a stressed/aroused state,” Baragli explained. “This is actually the opposite of many schools of thought, especially among horsemanship trainers. And the distinction is critical.”

This study was presented in September 2018 at the 14th International Equitation Science Conference in Rome and the abstract can be found in the proceedings. The work is now published in Scientific Reports Physiological outcomes of calming behaviours support the resilience hypothesis in horses, by C. Scopa, E. Palagi, C. Sighieri et al. It is open access and can be found here.

Editor’s note: When comparing the abstract of the study presented at 2018 ISES Rome with the journal article published in Nature, you will notice a difference in the terminology the authors have used to describe the respiratory sound produced by horses when presented with the novel object during the study. In the conference proceedings they use the term ‘snort’ and in the journal article they use ‘snore’ and give an explanation of their decision. Currently, there is no single ethogram with standardised definitions of behaviours that everyone agrees on, so for the purposes of this article, we have chosen to use the term ‘snort’ because after some consultation, it is one that most English-speaking horse people will relate to in this context. 

Christa Lesté-Lasserre

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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