Snorting horses are not indignant - a puff of the nostrils actually shows they're happy.
Researchers found equines snort more when feeding or freely roaming a pasture than they do while cooped up or working all week.
Scientists say their finding could help improve animal welfare by making it easier for owners to pick out when their horse is enjoying themselves.
Until now, a snort was thought to be a way for horses to clear dust from their airways or shoo away flies.
Researchers at the University of Rennes in France explained that trying to understand how a horse is feeling is a challenge to vets.
Anecdotal reports from horse owners indicate the animals produce more snorts when they are happy.
To investigate, scientists evaluated snorts among 48 horses in Brittany, France.
Some spent much of their time in individual stalls at a riding school where they worked between four and 12 hours a week.
The others lived in stable groups and were free to roam in their pasture.
The team found snorting was heavily linked with positive situations and a happy internal state, as shown by the ears pointing forward or sideways.
For example, riding school horses produced twice as many snorts in pasture than when they were in stalls.
Animals snorted most when they were eating, or during 'slow exploratory' walks, researchers found.
Overall during the tests, the horses snorted 560 times, ranging from one horse who snorted 0.75 times on average an hour, to a horse that snorted 12.8 times an hour.
No horse snorted when it was being aggressive to a human.
Taken together, the researchers said their findings suggest that snorts are reliable indicators of positive emotions in horses.
Study lead author Mathilde Stomp said: 'The snort, a non-vocal signal produced by the air expiration through the nostrils, is associated with more positive contexts (in pasture, while feeding) and states (with ears on forward position) in horses.
'Moreover, it is less frequent in horses showing an altered welfare.
'These results provide a potential important tool as snorts appear as a possible reliable indicator of positive emotions which could help identify situations appreciated by horses.'
Snorting may not just be a sign of happiness in horses. The author said that in her experience rhinos also snorted when in 'positive situations'.
The findings were published in the journal PLOS One.
This article has been adapted from its original source.
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