What is a Flehmen Response?

Discover why your horse is curling his upper lip.

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What is the Flehmen Response?
A horse exhibiting the flehmen response will curl his upper lip, raise his head, maybe turn his head from side to side, and make a bit of a snuffling sound. | Photo: Alexandra Beckstett/The Horse
Q: What does it mean when my horse raises his head and curls his upper lip?

A: This is one of my favorite behaviors! This is called the flehmen response. It is fun to see, but it is actually a mechanism to initiate some really cool activity in the brain.

If you watch a horse do a full out flehmen, he will curl his upper lip, raise his head, maybe turn his head from side to side, make a bit of a snuffling sound, and afterward there will be clear, watery droplets from the nostrils. In adult horses it’s seen most often in stallions when they’re testing vaginal secretions from mares or sniffing urine and manure.

The flehmen response is supposed to help move compounds such as pheromones, hormones, and others into the vomeronasal organ. The vomeronasal organ, or VNO, is a neat little structure that sits under the floor of the nasal cavity. Most animals have this, and humans seem to have a vestigial (functionless) one. In the horse access to the VNO is from a duct in the nasal passages (in other species the opening is at the roof of the mouth)

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Prior to attending veterinary school, Dr. Nancy Diehl completed a master’s degree in animal science while studying stallion sexual behavior. Later, she completed a residency in large animal internal medicine at the University of Pennsylvania’s New Bolton Center and worked in equine practices in Missouri and Pennsylvania. Diehl also spent six years on faculty at Penn State, where she taught equine science and behavior courses and advised graduate students completing equine behavior research. Additionally, Diehl has co-authored scientific papers on stallion behavior, early intensive handling of foals, and feral horse contraception. Currently she is a practicing veterinarian in central Pennsylvania.

One Response

  1. My horse does it when I’m next to him get is a 24 year old thoroughbred gelding why does he do it to me or other people

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