A horse's hooves are the animal's foundation. Unlevel, or unbalanced, hooves are impediments to soundness. The entire matter can take on a chicken-or-the-egg quality, as unsoundness and soreness in the horse can cause or exacerbate uneven hoof wear, while uneven hoof wear can contribute to lameness and soreness. Improper farriery, whether it comes in the form of forcing the hoof into a preconceived shape, or trimming incorrectly over the long term -- is a factor that can lead to hoof imbalance. It amounts to man-made causes of lameness. The impact and pressure exerted on the hoof is transferred up the leg and into the body of the horse where residual and continual soreness are created. Essentially, "unlevel" hooves cause dramatic health consequences for the horse and this is considered a serious issue.
Unbalanced hooves cause the horse to compensate as he moves and works under saddle. This compensation increases the uneven wear pattern of the hoof. Notice that the hoof wall will flare, wave or grow out unevenly. There will be chipping and unusually smooth areas of wall. Horses may also move with an unusual cadence or action. Shoes will show a lopsided wear pattern.
Unlevel hooves create additional strain on the leg as the horse compensates by shifting and carrying his weight in a forced manner. Such posture shifts create tendon, muscle and ligament soreness and injury. Horses will move in an odd manner and eventually experience long-term soundness issue such as arthritis or laminitis. Short-term results may include tripping or on-and-off lameness.
Saddle work exacerbates improper hoof balance. As the horse carries a rider in athletic pursuit he increases the strain on his body and legs. This leads to poor performance, reluctance to work and recurring lameness or soreness. Hoof issues increase leg, shoulder, back and neck strain and pain. Often these horses exhibit "sour" or reluctant attitudes, nervousness and reactivity, cold-backed reactions (bucking, rearing, agitation at saddling), and other behavioural problems relating to pain.
Unlevel hoof balance causes impediments to training. Long-standing incorrect hoof shape can take months or years to correct as the shape of the hoof must be slowly brought into balance (that is, into the correct or natural balance appropriate for each horse). Often the horse's legs and body have adapted to the unbalanced hoof and additional soundness issues will emerge from dramatic changes -- even if these alterations are beneficial. Horses that have had improper hoof balance may already have irreversible physical changes within the hoof structure as well as throughout their body.