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Why lamini­tis re­curs

Q:My 16-year-old warm­blood geld­ing is re­cov­er­ing from a rel­a­tively mild case of lamini­tis. It was al­most cer­tainly caused by un­usu­ally rich pas­ture con­di­tions, although he was used to be­ing turned out nearly 24-7. I now con­fine him to a pad­dock with sparse grass. He had no ro­ta­tion and is now sound. Can he ever be out on pas­ture again? Is there a safer time of day? I know spring and fall can be danger­ous, when the grass is at its best. How about mid­sum­mer, or af­ter the first killing frost? Hav­ing had lamini­tis once, is he more sus­cep­ti­ble to get­ting it again? Is there any­thing else I should know about his on­go­ing care? Mary Wash­burn Gard­ners, Penn­syl­va­nia

A:The num­ber-one thing to re­mem­ber if your horse gets lamini­tis is that the cause must be iden­ti­fied. Only by un­der­stand­ing why your horse de­vel­oped this po­ten­tially crip­pling in­flam­ma­tion of sen­si­tive lam­i­nae of the feet can you treat it ef­fec­tively and pre­vent a re­cur­rence.

To­day we un­der­stand that lamini­tis can de­velop in three ways:

The en­docrine path­way is by far the most com­mon form of lamini­tis. Also called “pas­ture-as­so­ci­ated lamini­tis,” this form of the dis­ease re­sults from el­e­vated lev­els of in­sulin0 in the blood. It tends to de­velop slowly, caus­ing sore­ness in the feet but not nec­es­sar­ily se­vere pain. Sep­a­ra­tion and dis­place­ment of the cof­fin bone from the hoof wall is likely to be grad­ual, if it oc­curs at all.

The in­flam­ma­tory path­way is as­so­ci­ated with fever and in­flam­ma­tion from in­fec­tions com­monly as­so­ci­ated

with di­ar­rhea or any sys­temic dis­ease. This form of lamini­tis tends to cause in­tense pain, and com­plete sep­a­ra­tion of the cof­fin bone from the hoof wall can de­velop within days.

The sup­port­ing-limb path­way de­vel­ops un­der me­chan­i­cal stresses, such as when a horse in­jures one leg and bears more weight on the op­po­site limb.

When pre­sented with a 16-year-old laminitic horse who has not had a fever or any signs of ill­ness and who has been graz­ing pas­ture 24-7, I would call for some sim­ple tests to see what is go­ing on with his hor­mones. A fast­ing (no food for four hours) blood sam­ple should be taken to check the horse’s blood in­sulin level as well as his level of the pi­tu­itary hor­mone ACTH (adreno­cor­ti­cotrophic hor­mone). Th­ese two tests can de­ter­mine if he has equine0 meta­bolic syn­drome (EMS) or pi­tu­itary0 pars in­ter­me­dia dys­func­tion (PPID), also known as Cush­ing’s dis­ease. Both of th­ese meta­bolic dis­eases can cause el­e­vated in­sulin lev­els, which in turn can lead to lamini­tis.

In the United States, grass-in­duced lamini­tis is al­most al­ways as­so­ci­ated with one of th­ese two con­di­tions, and if th­ese tests had been run when this horse first de­vel­oped lamini­tis, the ques­tion of whether the pas­ture was the cause would have been an­swered. I would sug­gest get­ting this horse tested even now be­cause ab­nor­mal hor­mone lev­els can con­tinue to cause low-grade lamini­tis, which may show no out­ward signs but can dam­age his feet.

If the tests come back as nor­mal or only slightly ab­nor­mal, I’d rec­om­mend run­ning an “oral sugar test.” In a fast­ing state, a blood sam­ple is taken and then a dose of light Karo syrup (70 ml/1,000 pounds body weight) is given orally; then a sec­ond blood sam­ple is taken in 90 min­utes. In a nor­mal horse the in­sulin level in the blood goes up from the dose of Karo syrup and drops again quickly, but in horses with EMS, the in­sulin re­mains high be­yond the 90-minute time.

If your horse has ab­nor­mal hor­mone lev­els, med­i­ca­tions, cou­pled with a di­etary and ex­er­cise pro­gram, can bring him back to health. Once he’s back to a nor­mal hor­monal state, the ques­tion of graz­ing can again be con­sid­ered. To be safe, most of th­ese horses are kept off the spring and fall grass, but they can graze dur­ing the sum­mer months.

Any bout of lamini­tis does per­ma­nent dam­age to the feet. The x-rays may ap­pear fairly nor­mal, but there are al­ways ir­re­versible changes to the at­tach­ments of the lam­i­nae. Any struc­ture in the body that is al­tered from its orig­i­nal state is more prone to break down in the fu­ture. So, yes, any horse who has had lamini­tis in the past is at an in­creased risk of get­ting it again.

For long-term care, I’d sug­gest that horses who have been di­ag­nosed with en­docrine lamini­tis have their hor­mone lev­els rechecked ev­ery six months. This will en­sure that the med­i­ca­tions are keep­ing them at nor­mal lev­els.

To­day, many horses with hor­mone ab­nor­mal­i­ties lead nor­mal lives with the as­sis­tance of med­i­ca­tions, diet and ex­er­cise pro­grams.

Don­ald Walsh, DVM

Homestead Ve­teri­nary Hos­pi­tal Villa Ridge, Mis­souri

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