Peach did not sur­vive her neu­ro­log­i­cal dis­ease, but we hope her case will pro­vide in­for­ma­tion that can save gen­er­a­tions of foals to come.

EQUUS - - Equus - By Gar­net Blatch­ford and Han­nah Aring­ton

A greater good: Peach did not sur­vive her neu­ro­log­i­cal dis­ease, but we hope her case will pro­vide in­for­ma­tion that can save gen­er­a­tions of foals to come.

In the spring of 2013, one of our fa­vorite mares gave birth to her first foal, a strap­ping bay colt we named Win­ston. At first, Win­ston was strong and ath­letic. We taught him to lead, longe and re­spond to other han­dling while his watch­ful mother stood nearby. On all counts, he seemed a healthy and promis­ing baby. Af­ter just a few weeks, how­ever, we could see that some­thing was wrong with Win­ston--he was be­com­ing weak and un­co­or­di­nated. We called our vet­eri­nar­ian out for an ex­am­i­na­tion.

The di­ag­no­sis was cer­vi­cal ver­te­bral com­pres­sive myelopa­thy (CVCM), com­monly called wob­bler dis­ease. A catchall term for com­pres­sion of the spinal cord, “wob­bles” in older horses is of­ten re­lated to arthritic changes or trauma, but in foals as young as Win­ston the con­di­tion is typ­i­cally due to mal­for­ma­tions and ab­nor­mal­i­ties of the ver­te­brae. Win­ston’s con­di­tion de­te­ri­o­rated rapidly, and soon he be­gan to have dif­fi­culty ly­ing down and get­ting up on his own. At this point, our fam­ily made the grim de­ci­sion to end his suffering and eu­th­a­nize him.

Sev­eral vet­eri­nar­i­ans we con­sulted told us that Win­ston’s case was an anom­aly and ex­tremely un­likely to re­oc­cur on our farm. And we had no rea­son to doubt that. We’d had two or three home­bred foals an­nu­ally on our farm for the pre­vi­ous nine years and not one had any known neu­ro­log­i­cal is­sues. So, af­ter a year of rest, we de­cided to give Win­ston’s dam an­other chance at mother­hood, match­ing her with a dif­fer­ent stal­lion. We wanted this healthy, kind and won­der­fully bred mare to have the op­por­tu­nity to raise a foal. In the spring of 2015, Hope was born. Her name sym­bol­ized the bright fu­ture that seemed to stretch ahead of her.

Hope was beau­ti­ful in every re­spect. She had a bright dun coat and her clas­si­cally ath­letic stock horse build was ev­i­dent from the be­gin­ning. As the months passed, we watched her grow, and her health ap­peared to be ex­cel­lent. But when she was 3 months old, Hope started show­ing signs of un­co­or­di­na­tion. We be­gan to fear that she had a milder form of the con­di­tion that had plagued Win­ston. We con­sulted the same vet­eri­nar­ian, who told us that we were again deal­ing with a case of wob­bler dis­ease. As time passed and her con­di­tion de­te­ri­o­rated, Hope strug­gled to get up on her own. By the time she was a wean­ling, we saw no other op­tion but to end her dis­com­fort. We had no faith that she could have had a com­fort­able life. We de­cided that Win­ston and Hope’s dam must not be a brood­mare. Even lack­ing sci­en­tific proof that wob­bles is a her­i­ta­ble con­di­tion, the only log­i­cal ex­pla­na­tion to us seemed to be that our mare was, due to some ge­netic or re­pro­duc­tive is­sue, pro­duc­ing off­spring with this prob­lem. Luck­ily, the mare was well-trained as a rid­ing horse, so we were able to find her a won­der­ful home with own­ers who agreed to our stip­u­la­tion that she never be bred again. We were over­joyed at her op­por­tu­nity

to be­gin a lovely new life.

Life on our farm went back to nor­mal. We watched our re­main­ing group of home­bred year­lings, 2- and 3-yearolds flour­ish, try­ing to heal from the loss of Win­ston and Hope.

More heart­break

Then in 2016, as usual, we had a small group of spring foals. One, a filly named Peach, was the first foal born to Plum, one of our fa­vorite rid­ing mares. At first every­thing seemed fine. When Peach was only a few days old we prac­ticed putting a lead on her and ask­ing her to walk along next to her mother. She seemed more sen­si­tive than the av­er­age foal and was prone to pulling back. This did not ap­pear terribly ab­nor­mal at first, but over the next month it be­came ap­par­ent that she lacked co­or­di­na­tion and bal­ance.

We started to panic. Peach’s dis­abil­ity was fright­en­ingly sim­i­lar to those we had seen be­fore. But how could it be the same is­sue? Every­thing we’d been told pointed to Win­ston and Hope be­ing un­for­tu­nate, iso­lated cases. Yet here we were again.

Con­sult­ing a dif­fer­ent equine vet­eri­nar­ian this time, we ex­plained the en­tire se­ries of events in de­tail. At this point, we were con­vinced there was an un­der­ly­ing cause. One small farm hav­ing three cases of wob­bler dis­ease in four years seemed im­prob­a­ble. Our first sus­pi­cion was an en­vi­ron­men­tal toxin or a nu­tri­tional de­fi­ciency, but the vet­eri­nar­ian thought th­ese were un­likely be­cause we feed high-qual­ity hay and a com­mer­cially pro­duced feed for­mu­lated for breed­ing horses. The vet­eri­nar­ian did find a sore area on Peach’s neck and pro­ceeded to take x-rays. A pos­si­ble area of in­flam­ma­tion was found near a growth plate, and the vet­eri­nar­ian rec­om­mended that we give her a few

months to im­prove. Over the next two months, her con­di­tion con­tin­ued to de­te­ri­o­rate. We were at our wits’ end.

In search of an an­swer, we be­gan scour­ing the in­ter­net for sci­en­tific lit­er­a­ture that might shed some light on what we were deal­ing with. Soon we came across re­search con­ducted by C.J. Finno, DVM, PhD, at the Univer­sity of Cal­i­for­nia—Davis. In one of her stud­ies, Finno de­scribed a Paint Horse breed­ing farm with a sit­u­a­tion that mir­rored our own. The horses on that farm had a vi­ta­min E de­fi­ciency, which trig­gered the de­vel­op­ment of clin­i­cal signs as­so­ci­ated with a hered­i­tary con­di­tion known as equine neu­roax­onal dys­tro­phy/equine de­gen­er­a­tive myeloen­cephalopa­thy (eNAD/EDM). We be­come con­vinced we were deal­ing with the same sit­u­a­tion. We con­tacted Finno and she gen­er­ously agreed to fly from Cal­i­for­nia to ex­am­ine Peach for her­self.

By the time Finno ar­rived at our farm with her re­search as­sis­tants, Peach was hav­ing trou­ble stand­ing. Af­ter only a short neu­ro­log­i­cal exam, Finno told me that she thought our filly could have eNAD/EDM---a dis­ease she has ded­i­cated her ca­reer to re­search­ing---and be­gan to fill me in on the de­tails of this dev­as­tat­ing con­di­tion.

A con­flu­ence of con­di­tions

Equine NAD/EDM, Finno told me, de­vel­ops in very young horses when two very spe­cific con­di­tions are met: a ge­netic sus­cep­ti­bil­ity and vi­ta­min E de­fi­ciency. That was sur­pris­ing to hear, given that we al­ways fed high-qual­ity hay and grain. But with­out reg­u­lar ac­cess to good pas­ture, horses can quickly be­come de­fi­cient in this nu­tri­ent. We pro­ceeded to check the vi­ta­min E lev­els of Peach, her dam and sev­eral other horses on the prop­erty. All were low or even crit­i­cally low. The nor­mal range of vi­ta­min E in blood is 2 to 4 μg/mL. Peach had a blood level of 0.6 μg/mL.

Vi­ta­min E is an an­tiox­i­dant, pro­tect­ing cells from the ac­tion of “freerad­i­cal” oxy­gen mol­e­cules that steal elec­trons. This is a cru­cial func­tion in rapidly grow­ing foals. With­out ad­e­quate an­tiox­i­dant pro­tec­tion, neu­rons and ax­ons through­out the body de­grade, lead­ing to in­co­or­di­na­tion and pro­gres­sive weak­ness. Mildly af­fected foals may have le­sions con­sis­tent with only eNAD (i.e., the mildest ver­sion of the dis­ease) whereas mod­er­ate to se­verely af­fected foals have more ex­ten­sive le­sions con­sis­tent with EDM. Foals can show signs of im­pair­ment as early as one month of age, and signs are usu­ally pro­gres­sive, be­gin­ning as clum­si­ness and ad­vanc­ing to se­vere dis­abil­ity. Af­fected horses

may have trou­ble back­ing up and ris­ing from a ly­ing po­si­tion. In se­vere cases, weak­ness is most eas­ily seen in the hind legs.

Not every foal de­fi­cient in vi­ta­min E, how­ever, will de­velop eNAD/EDM. Foals must also have a ge­netic pre­dis­po­si­tion to de­velop the dis­ease. Although the ex­act gene has yet to be lo­cated in horses, it is clear from Finno’s re­search that there is a her­i­ta­ble com­po­nent to eNAD/EDM, not just in Quar­ter Horses but also in many other breeds. This ge­netic pre­dis­po­si­tion likely ex­plains why Peach was af­fected by eNAD/EDM while other foals born on our farm that year were not, even though they all had low vi­ta­min E lev­els.

The ne­ces­sity of th­ese two fac­tors also ex­plains why the con­di­tion hardly ever ap­pears in foals born in ar­eas of the coun­try where lush pas­ture is read­ily avail­able. Even if they have the pre­dis­pos­ing ge­netic de­fect, their dams have plenty of vi­ta­min E to de­liver to the foal via colostrum , and then pas­ture pro­vides enough sup­ply as the foals’ diet shifts from milk to for­age. The abun­dance of lush pas­ture pro­tects the young­ster un­til the win­dow of risk ---thought to be about a year---passes. As Finno put it, “You prob­a­bly won’t see this dis­ease very of­ten in Ken­tucky, where lush pas­ture is avail­able for preg­nant mares and young foals.”

Finno went on to ex­plain that there is an iden­ti­cal syn­drome in chil­dren, who ap­pear nor­mal at birth but de­velop pro­gres­sive neu­ro­log­i­cal symp­toms due to a de­fect in the gene re­spon­si­ble for vi­ta­min E trans­port into cells. Anal­y­sis of the same gene in af­fected horses hasn’t turned up a cause for the de­fect, but Finno and her team are con­tin­u­ing to look. Once the ge­netic com­po­nent re­spon­si­ble is iden­ti­fied and the her­i­tabil­ity un­der­stood, sires and dams can be tested to de­ter­mine the risk of pro­duc­ing an af­fected foal. Then a dif­fer­ent pair­ing with a lower risk could be made, or other pre­ven­tive mea­sures could be taken--namely sup­ple­ment­ing the dam and new­born foal with vi­ta­min E. An ad­di­tional sup­ply of the vi­ta­min may pro­tect an af­fected foal’s neu­rons and ax­ons through the crit­i­cal growth pe­riod.

Leav­ing a legacy

All of this, how­ever, was too late for Peach. Finno in­di­cated that once neu­ro­log­i­cal signs of eNAD/EDM ap­pear, there is no way to re­verse them. The dam­age was done, and no amount of vi­ta­min E at this point could fix it. Fur­ther, the only way to know for sure if Peach had eNAD/EDM would be a necropsy, which would have to be per­formed im­me­di­ately af­ter she died. With that in­for­ma­tion, we made the gut-wrench­ing de­ci­sion to send Peach back to Cal­i­for­nia with Finno. We also sent an­other home­bred horse, a 7-yearold geld­ing with a pedi­gree sim­i­lar to that of Win­ston and Hope. When put in

train­ing, the geld­ing seemed so clumsy that we had de­cided he was not safe to ride. Finno had per­formed a neu­ro­log­i­cal exam on the geld­ing and told us she sus­pected that he may have eNAD/EDM as well. Now they would both be part of her es­sen­tial re­search.

A week af­ter she left our farm, Finno called to con­firm that Peach and the geld­ing both had dam­age in the re­gion of the brain­stem and spinal cord spe­cific to eNAD/EDM. Nei­ther horse had any patho­log­i­cal ev­i­dence of wob­bler dis­ease. Their tis­sues and ge­netic ma­te­rial would be­come clues in the search for the gene re­spon­si­ble for this ter­ri­ble dis­ease. As hor­ri­ble as it was to lose them, we take some com­fort in know­ing they contributed to this ef­fort.

With­out necrop­sies, there is no way to know for cer­tain whether Win­ston and Hope also had eNAD/EDM, but in our minds, there is no doubt. Finno ex­plained that many cases of eNAD/EDM are mis­di­ag­nosed as wob­bler dis­ease or, in older horses, equine pro­to­zoal myeloen­cephali­tis (EPM) that doesn’t re­spond to treat­ment or “re­turns” re­peat­edly. Many of th­ese horses man­age well enough at lib­erty but are too un­co­or­di­nated to carry a rider. They are la­beled “clumsy” or “unath­letic” when, in re­al­ity, they ac­tu­ally have a se­ri­ous prob­lem.

Since dis­cov­er­ing the cause of Peach’s dis­ease, we’ve changed the way we man­age our horses. We reg­u­larly check their vi­ta­min E lev­els, and we sup­ple­ment all horses, es­pe­cially brood­mares, to en­sure their colostrum is rich with the vi­ta­min. Be­cause the milk that fol­lows colostrum doesn’t con­tain much vi­ta­min E, we sup­ple­ment all new­borns with a liq­uid form of the nu­tri­ent un­til they are a year old. We are also tak­ing steps to im­prove our pas­tures and pro­vide our horses with more ac­cess to fresh grass, but liv­ing where we do, we will never be com­fort­able re­ly­ing on grass alone to ful­fill this cru­cial need.

We’ve also be­come ad­vo­cates for eNAD/EDM aware­ness and pre­ven­tive mea­sures in our lo­cal horse com­mu­nity. We share our mes­sage with any­one who will lis­ten: Horses who don’t have reg­u­lar ac­cess to high-qual­ity pas­ture are likely to be­come vi­ta­min E de­fi­cient, which can have se­ri­ous con­se­quences even in those not sus­cep­ti­ble to eNAD/ EDM. In our area, this is es­pe­cially im­por­tant to know. No one here has abun­dant pas­ture and, if they rely on baled for­age, they need to be aware of the risks. We en­cour­age horse own­ers to raise the ques­tion of eNAD/EDM with their vet­eri­nar­i­ans be­cause, un­for­tu­nately, this dis­ease is not widely rec­og­nized. We also pro­mote sup­ple­men­ta­tion of horses and brood­mares with vi­ta­min E. Sup­ple­men­ta­tion is rel­a­tively easy and we’ve al­ready seen the ben­e­fits on our farm---we had two foals born this past year who are grow­ing into per­fectly co­or­di­nated, strong, beau­ti­ful horses.

STAR-CROSSED: Peach ( left) and Hope ( be­low) started life look­ing healthy and vig­or­ous but a few weeks af­ter birth they be­came weak and un­co­or­di­nated.

PROB­LEM SOLVED: Since learn­ing of the source of Peach’s ill­ness, her owner has be­gun to mon­i­tor the vi­ta­min E lev­els of the horses on her farm, and all now re­ceive sup­ple­men­tal vi­ta­min E. So far, all new foals, in­clud­ing Nova ( above), have re­mained healthy.

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