Overreaching is a gait defect in horses that usually occurs at the trot. The hind foot moves forward and lands before the front foot has left the ground, catching and grabbing the front shoe or heel bulb. This can cause pulled shoes, cuts and soreness. For whatever reason, your horse's movement is not balanced, and it is not picking up its front feet in correct timing with its hind feet. There can be several causes, such as conformation, footing, training level, farrier work or how the horse is being ridden.
A horse's conformation can cause or contribute to overreaching. Horses with short backs and long limbs may have a tendency to overreach, particularly if they are also quite short in the forelimbs. If your horse is built "downhill," with its hips higher than its withers, that can cause overreaching as well. Very young horses are often downhill while growing, so often you will see foals overreach until their body shape and overall movement become more balanced. Meanwhile, do not ask your horse to perform an activity that is too energetic or difficult for its training level or ability.
Other conditions or situations can cause your horse to be imbalanced and thus tend toward overreaching. If it is not physically fit and is asked to perform manoeuvres such as too much lateral work, sharp turns or flying lead changes, or get into collected or extended frames, this can cause imbalance and overreaching. While fatigue can cause imbalance, so can excess energy or distractions, as the horse may not be paying attention to where its feet are. Pain can also cause imbalance, particularly an improper saddle fit that affects its shoulders and back. Paying attention to these possible issues may help you pinpoint the cause of your horse's overreaching.
Improper shoeing can cause overreaching, but shoeing adjustments can also help correct it, even if the shoeing was not the direct cause. If your horse has been trimmed or shod with a long toe and low heel, this frequently sets a horse up to overreach. Horses that go too long between shoeings or trims and thus have long toes can also have this issue. Your farrier can adjust your horse's breakover so that its front foot gets out of the way; tell your farrier that your horse is overreaching, and he should know what to do. Decreasing the time between shoeings can also help.
Heavy and deep footing can cause delays in the breakover of the front feet and thus cause overreaching. This can occur in deep sand, mud, snow or long grass. Make sure your arena sand is not too deep and is evenly distributed. If you need to ride in wet or muddy conditions, or in snow and long grass, consider adding studs to your horse's shoes for traction. It can take a horse time to get used to a traction device, and if it is not physically conditioned, it can actually injure ligaments and tendons, so exercise caution.