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Vesicular lesions on the feet usually develop first at either the cranial
or caudal ends of interdigital spaces. There is a progressive swelling
as vesicular fluid accumulates and the vesicles extend laterally and medially
to involve the coronary bands and the bulbs of the heels. This stage is
accompanied by heat and severe pain in the affected areas, which the animal
is reluctant to have palpated. The animal will have a tendency towards
recumbency and be reluctant to walk. When standing it will have a tucked-up
appearance and flick its legs intermittently.
The separation of the epithelium overlying vesicular lesions
from the tissues beneath results in a blanched effect. These changes and
the progressive accumulation of vesicular fluid, lead, in turn, to necrosis
of the epithelium and its rupture. Vesicles on the feet generally take
a day or so longer to rupture than those in and around the mouth. The
amount of walking done by an affected animal and the roughness of the
terrain will influence the speed and extent of both vesicle rupture and
the rate of healing of lesions. Secondary infection will delay healing
and can result in severe long-term effects to the feet.
In uncomplicated cases the healing of lesions on the feet
follows the same pattern as those in the mouth: there is an initial laying
down of sero-fibrinous tissue over the erosions to form a scab and a progressive
in-filling by the regeneration of the underlying epithelium. During these
processes the surrounding necrotic epithelium is sloughed off.
Damage to the coronary bands as a result of foot lesions
may interrupt the growth of horn so that when new horn grows the old one
may separate off.
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