It’s not uncommon to see professional riders go around with their horses' mouths lathered in white foam, dripping down their legs and chest. But how does this white foam appear and what actually is it?

Horses' saliva has very high concentrations of Latherin, which is a surfactant protein that can turn sweat and saliva into a foam-like substance. Horses have evolved to produce Latherin rich saliva in order to easily digest dry forage and improve thermoregulation. It is important to note that latherin only ‘foams’ up with friction. It would be alarming to see a horse out in the paddock excessively foaming from the mouth (and if this is the case call a vet immediately), however when a horse is being worked with a bit and bridle foamy lips are desired.

The friction and activity of the bit in the horse's mouth transform the Latherin saliva into a soapy-like substance creating ‘happy foam’. Similarly, when the horse is excessively sweating under saddle foam is created with the friction of the saddle pad. Horses have evolved to excrete protein-rich sweat in order to cut through their oily coat and facilitate water flow for evaporation and effective cooling. The term ‘happy mouth’ is used when a horse creates a foamy dribble, this is a good indication that the horse is happy and accepting of the bit as the tongue can relax and the jaw can supple under a soft hand.

Equidae, the taxonomic family of horses, have the most unique chemical makeup of sweat and saliva in the whole mammalian kingdom. They are the only mammals that produce excessive quantities of Latherin protein, whereas humans produce primarily water and electrolytes with minimal protein. RT-PCR screening conducted in research laboratories revealed Latherin transcripts are only present in horse epidermis and salivary glands, no other tissues (McDonald et al., 2009).

So, how do you get ‘happy foam’?

With a soft, kind hand and correct fitting bit, your horse will naturally produce foamy lips. Sweet iron bits are also a fantastic tool. When the sweet iron is exposed to saliva oxidation occurs creating a sweet, tingly sensation in the mouth which encourages salivation and ‘happy foam’.

GumBits are another fantastic alternative to encourage salivation. Essentially chewing gum for horses, encourages chewing activity, triggers salivation, and eliminates teeth grinding, horses also love the sweet taste. GumBits are made of all-natural FDA approved ingredients and are safe for horses.

References
McDonald, R.E., Fleming, R.I., Beeley, J.G., Bovell, D.L., Lu, J.R., Zhao, X., Cooper, A. and Kennedy, M.W. (2009). Latherin: A Surfactant Protein of Horse Sweat and Saliva. PLoS ONE, 4(5), p.e5726. doi:10.1371/journal.pone.0005726.