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LAMINITIS
“Laminitis is the inflammation of the sensitive laminae”.
Etiology:
Laminitis is caused by acute degeneration of the sensitive primary and secondary laminae of the hoof.
The cause of this degeneration is unknown. Situations that are associated with increased risk of laminitis includes
1) access to lush pasture ( suspected as the cause in 46% in the field)
2) grain overload (7%)
3) retained placenta (2%)
4) colic or diarrhea ( 3%)
Epidemiology:
Disease involving single animals. As a sequel to severe systemic disease including colic , diarrhea, metritis, and grain engorgement. Horses or ponies at pasture. Horses worked on hard surfaces. Obese horses and ponies. Horses with unilateral lameness may develop laminitis in the contralateral, supporting limb.
Pathogenesis :
The basic lesion of laminitis is the separation of the sensitive laminae of the third phalanx from the interdigitating laminae lining the internal surface of the hoof, so that the third phalanx drops through the hoof and comes to rest on the sole. Exactly the mechanisms is that links the risk factors listed above to the laminar degeneration, the basis of the separation is unknown. Briefly, the theories are:
a) Ischemia of the laminae with subsequent necrosis. Propoesed causes of ischemia include vasoconstriction development of arterio-venous shunts, interstitial edema, and presence of microthrombi in digital vessels. Ischemia due to microthrombus formation is considered an unlikely cause of laminitis. However there is evidence from experimental laminitis that changes in circulating concentrations of vasoactive amines or contractile activity of vessels in the hoof might contribute to ischemia.
b) Inflammation, with subsequent degeneration of sensitive laminae.
c) Enzymatic digestion of laminae by matrix metalloproteins (MMPs) induced by circulating factors including...