What Is The Flehmen Response?

The flehmen response (also called the flehmen posture, the flehmen position, and other similar names) is a behavior sometimes exhibited by horses when they encounter an interesting or stimulating scent.

In horses, the flehmen response is characterized by:

• A raised, extended neck and head.
• A simultaneous stiffening, raising, and curling of the upper lip.
• Inhaling (which might be difficult for observers to notice).

The mouth remains closed, or close to it, but the raised upper lip typically exposes some upper teeth.

Below: A horse exhibiting the behavior known as the flehmen response.

In addition to horses, the flehmen response has also been observed in a variety of other animals. While it may look a bit different, the flehmen response has been observed in cats (small and big), cattle, deer, elk, moose, rhinos, giraffes, goats, and more.

The Flehmen Response: What It Is

While most scientists aren't entirely sure why horses or other animals perform the flehmen response, most of them agree that it seems to be a way for the animal to transfer interesting or stimulating smells into the vomeronasal organ (VNO), also called Jacobson's organ.

This specialized organ processes these scents, which then go to the brain. As a result, the brain might trigger certain behaviors in response.

For example, stallions commonly flehmen when smelling the urine of a mare. This seems to be at least one of the ways a stallion detects the mare might be in estrus and receptive to breeding.

Below: Another horse exhibiting the flehmen response.

However, using the flehmen response to analyze scents isn't only about breeding. Stallions, mares, and geldings have all been observed performing the flehmen when encountering a variety of different scents. These scents might include urine or manure, new feed or feed supplements, an unknown scent floating on the wind, and more.

Below is the same mare shown at the top of the page exhibiting the flehmen response. When this photo was taken she had come to the feed truck along with a large herd of other mares.

Whether her flehmen response was due to the smells from the feed truck, the people in it, her herd mates, or some other stimuli isn't known.

Below: A mare showing the flehmen.

What The Flehmen Response Isn't

In a word, the flehmen response isn't a yawn. Some folks get them confused.

In horses, a yawn is recognized by:

• An extended neck and head that is typically close to level with the horse's back (not raised as in the flehmen response).
• The upper lip is raised, but not as stiffly as in the flehmen. Like the flehmen response, however, the upper teeth are often easily seen.
• The opening of both jaws, often very widely (not with the mouth closed, or close to it, as in the flehmen response).
• A deep inhale, followed by a deep exhale.

The exact reason horses and other animals yawn isn't always agreed upon among researchers. In general, though, it is thought to be a way to oxygenate the body, relax jaw muscles, or to help cool down after exertion.

Below: A yawning horse. Notice the level (not raised) head and neck, and that the jaws are open wide.

Here is another yawning horse. It also shows the wide-open jaws typical of a yawn, but not a flehmen response.