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Sev­eral neu­ro­mus­cu­lar dis­or­ders have been linked to vi­ta­min E de­fi­ciency:

• Equine mo­tor neuron dis­ease (EMND) is caused by the de­gen­er­a­tion of the mo­tor neu­rons, which con­trol the move­ment of the large mus­cles. “This af­fects the mo­tor neu­rons and there­fore the skele­tal mus­cles,” says Paul Si­cil­iano, PhD, of North Carolina State Uni­ver­sity. “In a horse with this prob­lem, you’ll see great ap­petite—eat­ing very well—but these horses waste away, los­ing mus­cle mass, and may die with­out in­ter­ven­tion.

“I ob­served this prob­lem first­hand in a group of blood donor horses main­tained at a vet­eri­nary hospi­tal,” Si­cil­iano adds. “They were fed the left­over hay from the prior year. It was good hay, not moldy, but it had been stored a long time. Over time, the hay grad­u­ally loses the com­pound that has vi­ta­min E ac­tiv­ity. The horses be­came vi­ta­min de­fi­cient and even­tu­ally de­vel­oped mo­tor neuron dis­ease.”

EMND does not de­velop quickly. “When stud­ies tried to repli­cate this in an ex­per­i­men­tal set­ting—to make horses de­fi­cient—it took nearly two years of feed­ing a low vi­ta­min E diet be­fore any signs oc­curred,” says Si­cil­iano. “When peo­ple see a prob­lem, they im­me­di­ately won­der what they’ve done to cause this change, but the re­al­ity is that the prob­lem oc­curred be­cause they didn’t change any­thing— the horse stayed on a de­fi­cient diet for a long pe­riod of time.”

• Equine de­gen­er­a­tive myeloen­cephalopa­thy (EDM) is caused by dam­age to the nerves in the spinal cord and parts of the brain. It typ­i­cally de­vel­ops in younger horses, those who are less than 2 years old, and it causes ataxia (in­co­or­di­na­tion) and loss of pro­pri­o­cep­tion (the sense of where their body and limbs are lo­cated).

EDM seems to run in fam­i­lies, which sug­gests that the cause is ge­netic. How­ever, the dis­ease is also char­ac­ter­ized by low lev­els of vi­ta­min E, and sup­ple­ment­ing with this nu­tri­ent helps horses im­prove. While low lev­els of vi­ta­min E do not ap­pear to be a di­rect cause of EDM, it’s pos­si­ble that a vi­ta­min de­fi­ciency could pro­duce the signs in a horse who is also ge­net­i­cally pre­dis­posed to the dis­ease.

• White mus­cle dis­ease, a de­gen­er­a­tion of the skele­tal mus­cles, is caused by a de­fi­ciency of se­le­nium, an­other po­tent an­tiox­i­dant. But low lev­els of vi­ta­min E also seem to play a role in the dis­ease. “Se­le­nium and vi­ta­min E are both im­por­tant for mus­cle func­tion and work as an­tiox­i­dants, but with slightly dif­fer­ent jobs,” Si­cil­iano says. Higher lev­els of one nu­tri­ent can help com­pen­sate for lower lev­els of the other, and signs of de­fi­ciency are more likely to oc­cur in horses with low lev­els of both.

• Spo­radic ex­er­tional rhab­domy­ol­y­sis (“ty­ing up”) is a se­vere, painful cramp­ing of the large mus­cles that can oc­cur dur­ing or just af­ter ex­er­cise. “Ex­er­tional rhab­domy­ol­y­sis has many causes, but one thought is that it can be caused by in­ad­e­quate lev­els of vi­ta­min E,” says Carey Wil­liams, PhD, an equine ex­ten­sion spe­cial­ist with Rut­gers, the State Uni­ver­sity of New Jer­sey. “Dur­ing re­search tri­als in my lab, we had a few horses that were mar­ginal in terms of plasma vi­ta­min E lev­els. They had more of a ten­dency to tie up dur­ing or af­ter the ex­er­cise, or at least be very mus­cle sore with higher lev­els of cre­a­tine ki­nase [a mus­cle en­zyme that is ab­nor­mally high in the blood when horses tie up]. Many peo­ple who have horses who suf­fer from ty­ing up prob­lems are feed­ing 5,000 IU of vi­ta­min E, and that does seem to help.”

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