Chronic laminitis is a sequel of acute inflammation of the sensitive laminae.  It varies as to intensity and the exact manner of its manifestation depends upon preexisting disturbances.

In some mild cases of laminitis there are recurrent attacks wherein no particular structural change exists, and diagnosis is established chiefly by noting the character of the pulse at the bifurcation of the large metacarpal (or metatarsal) artery just above the fetlock.  The same manifestation of pain is present when weight is supported by one foot, though in a lesser degree.  There is less local heat to be detected by palpation than in the acute cases.

Chronic laminitis as it occurs following acute attacks which have resulted in structural changes of the foot, present the same symptoms just described and, in addition, the peculiar alterations in structure exist.  When, owing to acute inflammation of the sensitive laminae, there has resulted necrosis of this sensitive tissue together with infiltration between the anterior surface of the distal phalanx (os pedis) and the contacting hoof, the lower portion of the distal phalanx is turned downward and backward (rotated upon its transverse axis).  Because of the traction which is exerted by the deep flexor tendon (perforans), as it attaches to the solar surface of the distal phalanx, this rotation is facilitated.  With hyperplasia of lamina, at the anterior portion of the distal phalanx, there results a thick “white line.”  Rotation of the distal phalanx necessitates a descent of its apical portion and there occurs a “dropped sole.”

In time, partly because of excessive wear of hoof at the heel, owing to an altered condition in the normal antagonistic relation between the flexor and extensor tendons, the toe makes an excessive growth, and the concavity of the anterior line is accentuated owing to this abnormal length of hoof.  The hoof, because of recurrent inflammatory attacks, is corrugated—­elevations of horn in parallel rings are usually present.

[Illustration:  Fig. 33—­The hoof in chronic laminitis.  Note the concavity.  This animal was serviceable for any work that could be performed at a walk.]

Animals that are so affected in traveling strike the heel first and the toe is later contacted with the ground surface.  Rotation of the distal phalanx upon its transverse axis produces a condition, with respect to this peculiar impediment, that is equivalent to added and excessive length of the deep flexor tendon.

Where there occurs suppuration, by careful inspection of the coronary region, one may early recognize detachment of hoof.  In such cases animals remain recumbent and, while the condition is not so painful at this stage, the practitioner must not overlook the real state of affairs.  History, if obtainable, will be a helpful guide in such cases.  Separation of hoof occurs as a rule in from four to ten days after the initial attack of acute laminitis.  Needless to say these cases are hopeless, when the economic phase of handling subjects is considered.