A horse is said to have a “hard” mouth when he has developed callouses in the corners of his mouth or dead spots on the bars of his mouth where nerve endings have been damaged. The more callouses or dead spots, the more pain he can take and the harder you will have to pull on him to get the response you want.
A horse that has had harsh treatment either from a severe bit or heavy handed reining techniques is less able to discern the pressure from the bit and does not respond quickly to the pressure cues.
It is recommended by some trainers that a young horse be trained in a bit that puts pressure onto the tongue more than on the bars in the early years thus saving bar pressure for a more mature horse with more training. His more sophisticated understanding of pressure (even othr body cues) will require less bar use and help prevent bar damage.
Some hard-mouth callouses can be recovered by a long, bitless vacation. However, dead spots may never recover.
Trainers often encounter hard-mouthed horses. Since a horse has several sensitive areas of his mouth, different bits can exploit different areas. For instance, a horse with dead bars might work well in a bit that exploits the tongue or palate instead of the bars. He may also work in a Bitless Bridle or a Hackamore.
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