Why do horses open their lips? Understanding the Flehmen Response and More

You've likely seen it before: a horse suddenly lifts its upper lip, often curling it back to expose its gums and teeth, sometimes with a vacant or almost comical expression. This peculiar behavior can leave onlookers scratching their heads, wondering what on earth is going on with their equine friend. While it might seem strange, this lip-lifting action is a fascinating and important way for horses to communicate and interact with their environment. The most common and widely recognized reason for a horse opening its lips is what's known as the Flehmen response.

The Flehmen Response: A Sensory Investigation

The Flehmen response, pronounced "FLEH-men," is a behavior observed in many species, including horses, cats, goats, and even some deer. It's essentially a way for them to "taste" or better analyze scents in their surroundings. When a horse performs the Flehmen response, it's not just being quirky; it's actively engaging its olfactory system in a very sophisticated manner.

Here's a breakdown of how and why it happens:

How it Works: The horse lifts its upper lip and curls it back, a movement that draws air into the nasal passages. Crucially, this action also closes off the nasal passage from the mouth. This allows the horse to draw scent molecules that have entered the mouth (often through licking or tasting something) up into a special organ called the vomeronasal organ, also known as Jacobson's organ.
What the Vomeronasal Organ Does: This organ, located in the roof of the mouth, is a secondary olfactory system. It's particularly adept at detecting pheromones – chemical signals that communicate information about reproductive status, social hierarchies, and even emotional states.
Why They Do It:
- Assessing Pheromones: This is the primary driver of the Flehmen response. Horses use it to gather crucial information about potential mates. A mare in heat will release pheromones that a stallion will immediately pick up on and investigate using the Flehmen response. Similarly, a stallion might Flehmen to assess the reproductive readiness of a mare.
- Investigating New or Interesting Scents: While pheromones are a big factor, horses will also Flehmen in response to other strong or unusual smells they encounter. This could be the scent of a new feed, a different horse, or even something from the environment that piques their curiosity. It's like a horse's way of saying, "Hmm, what is this I'm smelling?"
- Testing for Taste or Sensation: Sometimes, a horse might Flehmen after tasting something unusual or even something unpleasant. It's a way to further analyze the taste and potential effects of what they've ingested.

The Flehmen response is characterized by the distinct facial expression: the lifted upper lip, often wrinkled nose, and a slightly parted mouth. It can last from a few seconds to much longer, depending on the intensity of the scent being investigated.

Beyond Flehmen: Other Reasons for Lip Movements

While the Flehmen response is the most dramatic and noticeable reason for horses to open their lips, there are other, less dramatic reasons for lip movements:

1. Social Communication and Dominance

Horses are highly social animals, and subtle body language plays a significant role in their interactions. A less pronounced lip curl or a slight parting of the lips can be part of a broader communication strategy.

Establishing Dominance: In some social contexts, a horse might use a subtle lip curl as a mild threat or to assert its dominance over another horse. It's a less aggressive way of saying, "Stay back" or "This is my space."
Showing Affection or Appeasement: Conversely, a very soft, relaxed lip curl, often accompanied by relaxed ears and a soft eye, can be a sign of appeasement or even a subtle form of affection, particularly when interacting with a trusted human or a dominant horse they respect.

2. Reacting to Discomfort or Irritation

Sometimes, a horse's lip movements can signal that something is not quite right.

Dental Issues: If a horse is experiencing pain or discomfort in its mouth, such as from sharp points on its teeth or other dental problems, it might lift or move its lips in an attempt to alleviate the pressure or avoid chewing on that side.
Bit Discomfort: When a rider applies pressure with the reins, the bit sits in the horse's mouth. If the bit is ill-fitting, the pressure is applied too harshly, or the horse is simply uncomfortable with the bit, it might open its lips or curl them away from the bit as a reaction. This is a common sign that a rider should reassess their aids or the equipment.
Skin Irritation: In rare cases, a horse might lift its lips due to irritation on its muzzle or around its mouth from insects, allergies, or an injury.

3. Eating and Drinking

While not as dramatic as the Flehmen response, the simple act of eating and drinking involves opening the lips to some degree.

Horses use their lips and prehensile tongue to grasp food, like hay or grass, and bring it into their mouths. When drinking, they scoop water into their mouths by forming a cavity with their lips and tongue.

Understanding Your Horse's Signals

As an owner or handler, learning to interpret your horse's lip movements is key to understanding its needs and emotions. The context in which the lip lifting occurs is crucial. Consider:

The Environment: Is there a new horse nearby? A strange smell? A potential mate?
The Horse's Body Language: What are its ears doing? Its tail? Its eyes? Is the rest of its body tense or relaxed?
Recent Events: Has the horse just been ridden? Fed? Interacted with other horses?

By paying close attention to these details, you can decipher whether your horse is engaging in a sophisticated sensory analysis, communicating socially, or signaling discomfort.

Frequently Asked Questions (FAQ)

Why does my horse lift its lips and curl them back?

This is most likely the Flehmen response. Your horse is using a special organ in its mouth called the vomeronasal organ to get a better analysis of a scent, often pheromones from other horses or a strong, interesting smell in its environment.

When should I be concerned if my horse opens its lips?

You should be concerned if the lip opening is accompanied by other signs of discomfort, such as pawing, head shaking, or reluctance to eat or drink. It could indicate dental issues, bit discomfort, or other oral pain.

Is the Flehmen response a sign of a sick horse?

Generally, no. The Flehmen response is a normal, healthy behavior for investigating scents. It's only a concern if it's a new or unusual behavior for your horse, or if it's associated with signs of distress or illness.

Can horses control when they Flehmen?

While the initial trigger is an external scent, the active curling of the lips is a voluntary action. Horses choose to engage their vomeronasal organ to investigate scents they find particularly compelling or informative.