Founder is the term given when the distal phalanx (pedal
bone) becomes unstable within the hoof capsule, this occurs when the laminal
bond has been weakened and unable to continue transferring the weight of the horse or
pony from the skeletal structures through to the hoof capsule. Founder must not
be confused with laminitis (inflammation of the
laminae) as its founder that threatens the life of
the animal in question.Sink or rotate?
The distal phalanx usually founders in one of two ways, either 'rotating' or
'sinking' (sometimes a bit of both). The dorsal wall lifting theory proposes that pedal rotation is
associated with long narrow hoof shapes which distort at the toe and sinking is
frequently seen in hooves with rounder hoof shapes, where hoof capsule distortion is not just
focused at the toe but the whole hoof capsule becomes more generally enlarged.
This traumatises a larger area of laminae which causes the toe and heel areas of
the distal phalanx sink downwards within the hoof capsule.
Example
The pictures below show a horse
with different shaped hooves and illustrates the
concept of hoof shape determining if the distal
phalanx sinks or rotates.
Hoof capsule distortion is not obvious at this early stage and a disruption
ridge has not yet become visible, but a depression just above the coronary band
is palpable at the toe in the left foot. In the right foot the depression
extends towards each heel, which is consistent with sinking of the distal
phalanx.
The horse shown here has different hoof shapes on each limb, one narrow and
one rounder in shape. It is often stated that sinking is
seen in the more severe cases, but I believe that the hoof shape is the
main deciding factor. This unfortunate horse helps to illustrate this as
his right pedal bone has 'sunk' while the left pedal bone has 'rotated'.
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