It was recently asked “Does the bit hurt my horse?”. Although people might want to think otherwise, bits, and even bitless bridles do hurt horses. The pain can vary from mild to more severe. The mild pain can be simple pressure, and is generally not considered cruel. If fitted incorrectly, or if the horse has a wolf tooth, a bit can cause more unnecessary pain and discomfort. A rider with unsteady hands will cause more pain by jerking on the bit repeatedly.
The gentlest bit is the snaffle. This is a bit without shanks, there are many kinds of snaffles, some more harsh than others. The gentlest snaffle is not jointed and has a thick rubber mouth piece. The more joints a snaffle has (they often have only one joint) and the thinner the mouth piece, the more severe the bit. As well snaffles that have twists, ridges, and sharp edges, on the mouth piece will be severe.
photo source - the very gentle Mullen Snaffle, pictured above, with a far more severe snaffle, with twisted wire, pictured below.
Snaffles work by putting pressure on the mouth, lips, and against the jawbone. In most cases these are the first bits horses are introduced to in training, Western horses then progress to the curb bit (or some form of bitless bridle), while English horses (particularly those used in Saddleseat or Dressage) to on to the Double Bridle, or other form of bridle and bit combination. A good deal of pleasure horses remain ridden only with a snaffle, while horse shows often require mature horses to be fully trained into the full bridle, and bits that go with them.
Horses that wear snaffles are trained for direct reining, a pull on the right rein leads them to turn to the right, a pull on the left rein leads them to turn left. There are some indirect reining techniques as well.
author photo - showing the double bridle
In the double bridle, there is a tiny snaffle, known as the Bradoon, this is a very thin bit, used in combination with a curb type bit.
The curb bit is traditionally thought of as a Western bit, but this is not correct. It works by applying pressure on the jaws, and the high port puts pressure on the top of the mouth, it has leverage action which puts pressure on the top of the horses head (the poll), and with a chain (or leather strap) underneath the jaw it puts pressure there as well. The curb is by far, more severe than a normal snaffle, and if used incorrectly, or roughly, can cause undue pain and distress to a horse.
photo source - a typical western curb, in some cases the port (middle section in the mouth) is much higher.
The longer shanks from the mouth piece to the reins mean more leverage is created, thus a more severe bit. The higher the port in the mouth, the more pressure it will put on the top of the mouth, thus being more severe.
Occasionally a curb will be jointed, in such a case it has no high port, but will have the nutcracker effect on the horses lips and side of their jaws, as in a regular snaffle.
Horses who wear curb bits are generally trained on the snaffle first, then move into the curb. Once in the curb they are taught to respond to neck reining so pressure is not used on their mouth other than to keep the horses head in position, and often for speed control.
Curb bits are not for beginners, only a tiny amount of movement with the reins is needed for a horse to feel it in the mouth, and any harsh, or sudden, tugs will cause undue pain. Horses in distress from curb bits will often open their mouths and try to raise their head to get away from the pain.
photo source This horse is in pain and throwing his head to avoid it, you will note there is a "tie-down" on the horse so it cannot raise its head further.
This is often considered an English style bit, using two sets of reins, but is not quite as severe as the double bridle, which uses the bradoon (mentioned earlier) and an English curb. It is commonly used in polo, but really should be used by holding the reins in both hands. As with the double bridle, there are two sets of reins, and a rider must hold these in a way that they can control each separately.
photo source - you will note there is a bit of a cheat here, a strap connects the two rings of the bit and only one rein leads from each side to the riders hands. This bit is less severe than a curb, you will note the short shanks. Below is a picture of this system in use on a polo pony, clearly the animal is showing signs of pain and distress.
There are more types of bits than have been mentioned, but we can see that bits do cause pain, in some form or another, and it is this pain that we use to control them. There is no need to cause undue pain by using a bit incorrectly or by using too harsh a bit rather than better training. If a person is looking to buy a horse, they should always check the bit being used on the horse to see how severe it is. To be fair even bitless bridles work by inflicting pain, usually on the top of the horses head, or under the jaw.