EQUUS - - Special Report -

Over the past two decades, re­searchers have made great strides in un­der­stand­ing the causes of lamini­tis. Three pri­mary path­ways lead­ing to the dis­ease have been iden­ti­fied:

• The in­flam­ma­tory path­way is as­so­ci­ated with fever and in­flam­ma­tion from in­fec­tions com­monly as­so­ci­ated with di­ar­rhea or any sys­temic dis­ease, such as Po­tomac horse fever. This form is also as­so­ci­ated with con­cus­sion to the feet, ex­po­sure to black wal­nut shav­ings or in­ges­tion of toxic plants. The in­flam­ma­tory form, re­ferred to as “acute lamini­tis,” tends to cause in­tense pain and mas­sive sep­a­ra­tion of the lam­i­nae, caus­ing the cof­fin bone to sep­a­rate from the hoof wall and de­scend down­ward in the foot, which can de­velop within days of the on­set. In the most se­vere cases the bone de­scends through the sole to the ground.

• The sup­port­ing-limb path­way de­vel­ops un­der me­chan­i­cal stresses, such as when a horse has in­jured one leg and is re­quired to sup­port all of his weight on the op­po­site limb. The me­chan­i­cal stress on the sup­port­ing limb re­sults in lamini­tis oc­cur­ring in the foot.

• The en­docrine path­way is by far the most com­mon form of lamini­tis seen to­day. Also called “pas­ture­as­so­ci­ated” or “grass lamini­tis,” this form of the dis­ease re­sults from el­e­vated lev­els of in­sulin in the blood. It is seen in horses who have EMS or PPID. It tends to de­velop slowly, is some­times called “chronic lamini­tis” and causes sore­ness in the feet, but not nec­es­sar­ily pain as se­vere as in the acute form. Sep­a­ra­tion and dis­place­ment of the cof­fin bone from the hoof wall still oc­curs but is likely to be grad­ual. Re­peated bouts re­sult in per­ma­nent de­for­mity of the feet, crip­pling the horse. Eat­ing grass in the spring and fall are as­so­ci­ated with in­creas­ing lev­els of in­sulin that ini­ti­ate a bout of painful lamini­tis. In this form of the dis­ease ex­cess in­sulin causes the lam­i­nae to lengthen and weaken, re­sult­ing in ab­nor­mal growth rings on the hoof. Even­tu­ally, the bone de­scends down­ward, pro­duc­ing lamini­tis.

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