What is Flehmen?
The action you are talking about (curling open the lips to expose the teeth) is most likely to be a FLEHMEN RESPONSE. It is a German word in origin which means "to twist the mouth" and involves the upper and lower lips curling back. The horse is one of the animals which has a vomeronasal organ, or VMO (often referred to as the Jacobson's Organ) in the roof of the mouth. In drawing back the lips, smells are run over the organ where it detects chemical compounds, especially pheromones. What the horse is doing in effect, is to draw in the smell and then close the nostrils to allow for maximum exposure to the VMO for chemical analysis. Stallions often display this pose when smelling a mare's urine to detect whether she is in heat. Horses will also display the Flehmen response when they smell unususal smells like onions, perfumes and other things that are unfamiliar to them. It is also very interesting to note that the Flehmen response is often seen in horses with gastro-intestinal discomfort and can be an indicator of colic. Curling the lips back and 'smiling' has also been commonly seen in horses with ulcers. Some horses do this at feedtimes to show their irritation at having to wait for food to arrive. (Although, again, some people feel that because the horse may have ulcers, he is doing it in anticipation of pain while eating.) Horses that curl their lips back when tacked up are often doing so because of an ill-fitting bridle and bit in the mouth. I hope that this helps you understand what your horse is doing. If he seems to be doing it too often, or you notice something else is amiss, it may be worth your while having him checked over by a vet. Enjoy him - he sounds like a gem!
at 5:30 PM