Why do some horses foam up their bit and lips?
Because they can. All sarcasm aside, it’s perfectly natural for a horse to foam around the lips as he is being ridden. It’s commonly seen in dressage horses, and perhaps this is the best example to explain how the foam happens in the context of dressage. (Bear with me a sec even if you are not a dressage rider…)
In dressage, the horse is considered supple (strong and flexible) and carrying his own weight when he can lift his back and have the energy in his hind legs travel over his lifting top line, through the neck, over the poll, and down to the mouth. His muscles are soft and strong, the horse is not braced, rigid, or stiff. In this state of suppleness, his salivary glands are stimulated to produce more saliva, typically because of the positioning of his body. The saliva then collects in his mouth, where a supple and soft jaw and tongue move around.
Latherin and motion make the foam!
Combine this saliva production, mouth movement, and the substance latherin (this also makes sweat foam) and you get some foamy lips. It’s perfectly safe. It’s not a sign the horse is abused, overworked, or in pain. It’s also not a direct result of your horse wearing a bit. Horses ridden without bits can (and do) foam at the mouth.
Many of us have ridden horses with “hard mouths”. It’s not fun for anyone. A hard mouthed horse will not foam at the mouth, and he will also be stiffer in his body and more uncomfortable to sit the jog or trot. If I recall correctly, it’s also easier to get into a tug of war on a hard mouthed horse. It’s not wrong to be hard mouthed, but it’s something that proper training and riding can address, if you like.
Migs gets a foamy mouth when he eats his hay pellets - lots of chewing and saliva.
Now…there are also some instances in which a foamy mouth can mean TROUBLE with a capital T. Oral ulcers, such as in the case of the viral vesticular stomatitis, gum diseases, and choke can all create foamy lips. A twig, stick, or other foreign body stuck in your horse’s mouth can also do this. Let’s not forget about some toxic plants, clovers that cause slobbers, and even rabies, a 100% fatal disease.
The key idea here is that if your horse suddenly starts foaming at the mouth, call your Veterinarian ASAP. And don’t sweat it if he never starts to get foamy lips while being ridden, that’s not a big deal either!