EQUUS - - Conformati­on Insights -

Sy­rocco Rime wasn’t di­ag­nosed with a my­ofib­ril­lar my­opa­thy (MFM) un­til long af­ter she re­tired from elite en­durance com­pe­ti­tion.

“I had bred Rime my­self and started rid­ing her when she was 4,” says Meg Sleeper, VMD, a ve­teri­nar­ian who spe­cial­izes in car­di­ol­ogy. “I re­mem­ber her ty­ing up at two com­pe­ti­tions. The first time was very mild, so mild that none of the race vet­eri­nar­i­ans knew it was hap­pen­ing and I wasn’t ex­actly sure my­self what was go­ing on. But we pulled blood af­ter the race and found el­e­vated mus­cle en­zymes, so it was clear it was some type of ty­ing up. It hap­pened a sec­ond time at the 2005 Pan Am Cham­pi­onships. By then, I knew she was pre­dis­posed to ty­ing up so I rec­og­nized it and with­drew her right away.”

Still, Rime’s episodes didn’t look like clas­sic cases of ty­ing up, says Sleeper. “The mus­cles over her croup would get a lit­tle tight, but her gait wasn’t re­ally af­fected,” she says. “If you weren’t sit­ting on her and didn’t pay close at­ten­tion, you

could miss it EARLY CASE: Sy­rocco Rime’s en­tirely.” episodes of Through ty­ing up were re­search the re­sult of a and a bit con­di­tion later of trial and de­fined as er­ror, Sleeper my­ofib­ril­lar learned how my­opa­thy. to man­age

Rime’s ty­ing up with a low-starch diet and ex­er­cise. The mare was able to com­pete for sev­eral years with­out any fur­ther episodes, but even­tu­ally she de­vel­oped uveitis and was re­tired due to blind­ness at age 10. By then, Sleeper was bring­ing her full sis­ter, Sy­rocco Reveille, up through the en­durance ranks. It soon be­came clear, how­ever, that Rime’s younger sib­ling also had a pre­dis­po­si­tion to ty­ing up.

“Rev never tied up dur­ing com­pe­ti­tions,” says Sleeper. “But she did once or twice dur­ing con­di­tion­ing. By then I was aware of the prob­lem and knew I had to man­age her.”

Although she knew her horses were prone to ty­ing up, Sleeper didn’t have a more pre­cise di­ag­no­sis un­til she met Stephanie Val­berg, DVM, PhD, who heads a lab­o­ra­tory ded­i­cated to re­search­ing the var­i­ous types of equine mus­cle my­opathies. Hav­ing iden­ti­fied causes of ty­ing up in stock breeds, Thor­ough­breds and warm­bloods, Val­berg had turned her at­ten­tion to Ara­bi­ans. “I had heard that Dr. Val­berg was look­ing for Ara­bi­ans with a his­tory of ty­ing up,” says Sleeper. “She had al­ready ap­proached the en­durance rid­ing com­mu­nity and was re­ferred to me by a fel­low rider who knew I had been deal­ing with these is­sues.”

Af­ter sev­eral phone calls to dis­cuss Rime and Rev’s his­tory, Val­berg trav­eled to New Jer­sey and did blood­work and biop­sies on Sleeper’s horses.

Sleeper said she wasn’t sur­prised when the biop­sies from Rime and Rev and one other horse re­vealed they had PSSM. “Af­ter talk­ing with [Val­berg], that is what I’d ex­pected.” At that time, Val­berg knew Ara­bi­ans had a vari­a­tion of PSSM in which the glyco­gen in mus­cle cells clumps ab­nor­mally, but the con­di­tion was still be­ing in­ves­ti­gated and didn’t yet have its own name.

The next year, how­ever, Val­berg pub­lished a pa­per de­scrib­ing MFM. “For me the only thing that changed is it fi­nally has a name,” says Sleeper. “We fig­ured out the man­age­ment long ago.”

Ex­er­cise is key in keep­ing MFM horses healthy, says Sleeper. Her horses live out­side 24 hours a day and come in­side only to eat. Although she’s blind, Rime stays ac­tive enough in the herd to stay healthy, but the rest of the horses have some for­mal ex­er­cise ev­ery day.

“To man­age this, they need to be kept in work ev­ery sin­gle day,” says Sleeper. “Even when they have a day ‘off’ they usu­ally go on the eu­ro­ciser [horse walker]. Reg­u­lar ex­er­cise keeps the glyco­gen mov­ing out of the cells. If the mus­cles are full of su­gar and you ask a lot of the horse, that’s when you can have trou­ble. You don’t have much room for er­ror. To be suc­cess­ful with horses who have this, you’ve got to stay on top of things and not get lazy or cut cor­ners.”

While the ge­net­ics of MFM aren’t un­der­stood, Sleeper says she is cer­tain it’s in­her­ited, given the pat­terns she has seen in her own re­lated horses. “That brings up the ques­tion, ‘Should I breed a horse who has this?’ From my back­ground as a vet­eri­nary car­di­ol­o­gist, I know that you have to be care­ful when try­ing to erad­i­cate in­her­ited diseases be­cause in the process you can breed out good ge­netic ma­te­rial. I also strongly be­lieve that MFM is found in the high­est class of ath­lete, so do we want to re­move them from the gene pool en­tirely? If the con­di­tion wasn’t man­age­able that would be dif­fer­ent, but this is man­age­able and these horses can still com­pete suc­cess­fully and con­trib­ute to the breed.”

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