Tendency to lie down whenever possible, and recumbency in extreme cases
Change in the outward appearance of the hoof in cases of chronic laminitis: dished (concave) dorsal hoof wall, "founder rings" (growth rings that are wider at the heel than the toe), a sole that is either flat or convex just dorsal to the apex of the frog which indicates P3 has displaced or penetrated, widening of the white line at the toe with or without bruising, "clubbing" of the foot. Change in the appearance of the coronary band: hair that does not lie in a normal position (not against the hoof wall), indentation or rim just above the hoof capsule allowing palpation behind the coronary band. In cases of sinking, it may be possible to palpate a groove between the coronary band and the skin of the pastern. Lameness evaluation
Hoof testingLaminitic horses are generally sore to pressure from hoof testers applied over the toe area. However, there is risk of a false negative if the horse naturally has a thick sole, or if the hoof capsule is about to slough. Obel grading systemThe severity of lameness is qualified using the Obel grading system:
Obel grade 1: Horse shifts weight between affected feet or continuously lifts feet up. It is sound at the walk but displays a shortened stride at the trot. Obel grade 2: Horse displays a stilted, stiff gait, although is willing to walk. It is possible to easily lift a front foot and have the horse take all of its weight on the contralateral limb.
Venograms will have relatively normal contrast distribution, including to the apex and distal border of the coffin bone, and the coronary band, but "feathering" may be present at the lamellar "scar. "Uncompensated cases will develop a lamellar wedge (pathologic horn), leading to a poor bridge between P3 and the hoof capsule. This will lead to irregular horn growth and chronic lameness, and horses will suffer from laminitis "flares." Inappropriate hoof growth will occur: the dorsal horn will have a tendency to grow outward rather than down, the heels will grow faster than the toe, and the white line will widen, leading to a potential space for packing of debris. The solar dermis is often compressed enough to inhibit growth, leading to a soft, thin sole (<10 mm) that may develop seromas. In severe cases where collapse of the suspensory apparatus of P3 has occurred, the solar dermis or the tip of P3 may penetrate the sole. The horse will also be prone to recurrent abscessation within the hoof capsule. Venogram will show "feathering" into the vascular bed beneath the lamellae, and there will be decreased or absent contrast material in the area distal to the apex of the coffin bone. Causes
Laminitis has various causes, some of which commonly occur together. These include:

Vasoactive amines
The inflammatory molecule histamine has also been hypothesized as a causative agent of laminitis. However, contradictory evidence indicates the role of histamine in laminitis has not been conclusively established.