EQUUS - - Immune Function -

Al­though it can’t quite be con­sid­ered nor­mal, pi­tu­itary pars in­ter­me­dia dys­func­tion (PPID, col­lo­qui­ally known as Cush­ing’s syn­drome) is very com­mon in older horses. An es­ti­mated 70 per­cent of horses over age 25 have some de­gree of PPID.

In horses with PPID, a mal­func­tion of the pi­tu­itary gland in­side the brain causes the se­cre­tion of ex­ces­sive lev­els of the hor­mone adreno­cor­ti­cotropin (ACTH). This then trig­gers the adrenal gland to in­crease the pro­duc­tion of cor­ti­sol, and the re­sult­ing im­bal­ances lead to the hall­marks of PPID: a long, shaggy hair­coat that is slow to shed, lethargy, loss of mus­cle mass, lamini­tis and sus­cep­ti­bil­ity to in­fec­tion. Iden­ti­fy­ing and con­trol­ling PPID is an im­por­tant part of main­tain­ing an older horse’s health and well-be­ing. That means it's a good idea to test any older, slightly shaggy horse for PPID. The two most com­monly per­formed test are the ACTH test which is a one-time blood test that mea­sures lev­els of ACTH, and the thy­rotropin-re­leas­ing hor­mone (TRH) stim­u­la­tion test which com­pares the level of ACTH be­fore and af­ter ad­min­is­tra­tion of TRH. The test or com­bi­na­tion of tests that will be best for your horse de­pends on sev­eral fac­tors in­clud­ing his over­all health, the time of year and your ge­o­graphic area. Your ve­teri­nar­ian will know which test is most suit­able for your sit­u­a­tion.

If your horse re­ceives a PPID di­ag­no­sis, you can take im­me­di­ate steps to limit the con­di­tion’s ef­fects. Per­golide me­sy­late (prod­uct name Pras­cend) is the only med­i­ca­tion ap­proved by the Food and Drug Ad­min­is­tra­tion for treat­ing the dis­or­der.

In ef­fi­cacy stud­ies, 76 per­cent of horses showed some im­prove­ment in their clin­i­cal signs within 30 days of start­ing per­golide treat­ment. Within six months, 89 per­cent of horses had im­proved hair­coats and 46 per­cent showed im­prove­ment in mus­cle tone. One im­por­tant point: Cheaper ver­sions of per­golide of­fered through some com­pound­ing phar­ma­cies are il­le­gal, and stud­ies have shown them to be un­sta­ble and prob­a­bly in­ef­fec­tive be­cause of ex­tremely spe­cific stor­age needs of com­pounded for­mu­la­tions.

In ad­di­tion to giv­ing your horse med­i­ca­tion for PPID, you can keep him more com­fort­able by clip­ping a slow-to-shed coat when spring ar­rives. Also, be­cause PPID is linked to a higher in­ci­dence of lamini­tis, con­sider switch­ing to a feed that is low in sug­ars and non­struc­tural car­bo­hy­drates to avoid trig­ger­ing an episode— and be ex­tremely care­ful about putting a horse with PPID on lush pas­ture in the spring and fall. Rou­tine hoof care is es­pe­cially im­por­tant for horses with the con­di­tion, as are reg­u­lar vac­ci­na­tions and par­a­site con­trol.

A horse with PPID will need to re­main on med­i­ca­tion for the rest of his life. The good news is that per­golide tends to work well and the con­di­tion can be suc­cess­fully man­aged for many years.

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