Why does my horse curl his upper lip? 


This is called the flehmen response, and many animals demonstrate this behavior.  The typical flehmen response also includes raising and stretching the neck while curling the upper lip and exposing the teeth.  Cats, horses, rhinos, and even hedgehogs have this response. It’s used for a few reasons, mainly to help with your horse’s sense of smell.  The flehmen response acts in conjunction with the vomeronasal organ near the palate to amplify smells.  Those smells are usually horse related smells, like manure and urine, but also include other novel smells that your horse may find while cruising around doing horse things. Fancy, right?  



Not a horse to hide his feelings about wormers, this is the flehmen response after a dose.  


In horses, stallions exhibit this behavior quite a bit, especially around the ladies.  Mares will often demonstrate the flehmen response after giving birth.  Geldings are the group of horses that rarely demonstrate the flehmen response, but you will still find they will.   I have known horses that are obsessed with other horse’s manure, in the paddocks, in the ring, in the cross tie bins and will regularly display the flehmen response.  Other horses do so after eating something horrible (like a wormer), or even if they are looking for just the right spot to roll in the field.  



The flehmen response, complete with extended and lifted head and neck.  


Most horses will also display the flehmen response when they are in pain, usually with abdominal pain.  I have seen horses do this, and they may not raise their heads and necks, so all you see is the upper lip curling or twitching.  


When does your horse display the flehmen response?