Cop­ing with Equine Metabolic Syn­drome

Find out how to di­ag­nose, treat and man­age a horse who has equine metabolic syn­drome, a se­ri­ous en­docrine dis­or­der.

Practical Horseman - - Contents - By Les­lie Threlkeld

He looks ‘healthy,’” your trainer says of your horse, who has re­cently packed on a few ex­tra pounds. Al­though you laugh off the com­ment, you won­der why re­duc­ing his feed and adding a few more min­utes to his trot sets and flat­work hasn’t slimmed him down at all. It’s pos­si­ble the an­swer lies not in his meal size or ex­er­cise regime but in his blood­stream. He may be

ex­pe­ri­enc­ing the ef­fects of an en­docrine dis­or­der called equine metabolic syn­drome, which af­fects his abil­ity to me­tab­o­lize food prop­erly.

The en­docrine sys­tem is made up of mul­ti­ple or­gans, glands and tis­sues whose pri­mary roles are hor­mone pro­duc­tion and reg­u­la­tion. When th­ese hor­mones are re­leased into the body, they power many sys­tems, such as re­pro­duc­tion, growth and me­tab­o­lism. When the en­docrine sys­tem isn’t func­tion­ing prop­erly, it can lead to com­pli­ca­tions. In horses, one of the most com­mon en­docrine dis­or­ders is EMS, which can be a se­ri­ous health risk if it is not treated and left un­man­aged.

EMS oc­curs in young to mid­dle-aged horses and is most com­monly seen in breeds that you might call “thrifty” or “easy keep­ers,” such as Mor­gans, An­dalu­sians, Ara­bi­ans, Paso Fi­nos, ponies, minia­tures and warm­bloods. Re­search in­di­cates that breeds like th­ese are at a higher risk of EMS due to ge­netic pre­dis­po­si­tion.

“Th­ese are in many re­spects good genes,” says Ni­cholas Frank, DVM, PhD, DACVIM, a pro­fes­sor of Cum­mings School of Vet­eri­nary Medicine at Tufts Uni­ver­sity. “They were genes that al­lowed th­ese breeds to sur­vive. The pony that could put on a lot of weight would then sur­vive long win­ters when there wasn’t much avail­able to eat. The genes stayed in the blood­lines be­cause the horses could sur­vive.”

Sci­en­tists and vet­eri­nar­i­ans are still try­ing to un­der­stand the ex­act na­ture of th­ese hered­i­tary con­nec­tions as well as why some horses are more se­verely af­fected by EMS than oth­ers. De­spite the re­main­ing un­knowns, the dis­or­der can be ef­fec­tively treated and even pre­vented through horse man­age­ment and nu­tri­tion con­trol.

Rec­og­niz­ing Early Signs

The pri­mary char­ac­ter­is­tic of EMS is in­sulin re­sis­tance, now more com­monly re­ferred to as in­sulin dys­reg­u­la­tion. The horse’s pan­creas, an im­por­tant or­gan of the en­docrine sys­tem, pro­duces and reg­u­lates the re­lease of in­sulin, a hor­mone that func­tions to me­tab­o­lize and bal­ance the body’s main source of fuel, glu­cose. Glu­cose is a su­gar con­verted from car­bo­hy­drates in for­age and grain. The more glu­cose there is in a horse’s diet, the more in­sulin the pan­creas pro­duces. Horses with EMS pro­duce too much in­sulin. Over time, their bod­ies stop re­spond­ing, or be­come re­sis­tant, to the hor­mone’s ef­fects, so their pan­creases have to pro­duce even more in­sulin to be ef­fec­tive.

“In any horse, in­sulin con­cen­tra­tions are go­ing to go up af­ter they feed, but in the horse with in­sulin dys­reg­u­la­tion, those in­sulin con­cen­tra­tions go up much higher,” Dr. Frank says. In­sulin causes glu­cose to go into the tis­sues, where it is used to power bod­ily func­tions or is stored as fat, he ex­plains. “While EMS horses are able to do this and main­tain glu­cose con­cen­tra­tions in nor­mal range, they have to se­crete a lot more in­sulin to do so.”

Be­cause in­sulin stim­u­lates con­ver­sion of glu­cose into fat, high con­cen­tra­tions of it may even pro­mote ex­cess fat ac­cu­mu­la­tion. Clin­i­cal signs as­so­ci­ated with EMS in­clude obe­sity, dif­fi­culty los­ing weight, eas­ily gain­ing weight and the de­vel­op­ment of fatty de­posits, par­tic­u­larly in the crest of the neck. EMS horses may also have in­creased in­flam­ma­tory re­sponses.

Obe­sity com­monly as­so­ci­ated with EMS horses can have neg­a­tive ef­fects on the body, in­clud­ing the for­mu­la­tion of pe­dun­cu­lated lipo­mas (be­nign tu­mors on the con­nec­tive tis­sue of the in­tes­tine), which

can lead to in­testi­nal colic. The added weight on joints and other mus­cu­loskele­tal struc­tures can also be dam­ag­ing to horses. In ad­di­tion, high lev­els of in­sulin con­cen­tra­tions are thought to be re­lated to changes in mares’ re­pro­duc­tive cy­cling, which may de­crease the like­li­hood of con­cep­tion.

The most se­ri­ous ef­fect of un­hin­dered EMS is lamini­tis, a painful and po­ten­tially life-threat­en­ing con­di­tion of the horse’s feet. Lamini­tis is the break­down of lam­i­nae, the in­ter­nal struc­tures that hold the wall of the hoof to the cof­fin bone. This pro­duces lame­ness and down­ward ro­ta­tion of the cof­fin bone, and in very se­vere cases, it may even cause the wall and the bone to sep­a­rate. The con­nec-

tion be­tween high lev­els of in­sulin and lamini­tis is still un­clear, but the risk is real and can af­fect a horse’s qual­ity of life.

“It isn’t al­ways their en­docrine sys­tem we’re left man­ag­ing af­ter a bad bout of lamini­tis; it’s the struc­tural dam­age to the feet,” Dr. Frank says.

Sim­ple Blood Tests Di­ag­nose EMS

EMS can be defini­tively di­ag­nosed with sim­ple blood tests. Clin­i­cians and re­searchers in the Equine En­docrinol­ogy Group, of which Dr. Frank is a mem­ber, work to­gether to ad­vance the un­der­stand­ing of en­docrine dis­or­ders in horses. They up­date their web­site ( www.sites.­dogroup) ev­ery two years with di­ag­nos­tic rec­om­men­da­tions based on the lat­est en­docrine-dis­or­der re­search. Cur­rently, the group rec­om­mends two blood tests for di­ag­nos­ing EMS: the oral su­gar test and the in­sulin tol­er­ance test. Both can be per­formed at the barn and are in­ex­pen­sive.

Oral Su­gar Test: This is the test most com­monly used for di­ag­nos­ing EMS, as it repli­cates what hap­pens to an in­di­vid­ual horse’s glu­cose lev­els when he eats and, con­se­quently, can eval­u­ate his nat­u­ral in­sulin re­sponse. It cal­cu­lates how much in­sulin is pro­duced as a re­sult of a mea­sured dose of glu­cose be­ing de­liv­ered into the body. The horse must fast for six hours first. Then the test is per­formed by ad­min­is­ter­ing corn syrup by mouth. To mea­sure the sub­se­quent in­crease of in­sulin con­cen­tra­tions, blood sam­ples are taken at 60 and 90 min­utes af­ter the corn syrup is given. If the horse has in­sulin dys­reg­u­la­tion, his in­sulin con­cen­tra­tions will go up higher than a nor­mal horse’s would in that pe­riod of time.

Al­though lamini­tis has been as­so­ci­ated with in­stances of high su­gar in­take (for ex­am­ple, from a grain over­load), Dr. Frank stresses that nei­ther he nor his col­leagues have ever ob­served a horse with EMS de­velop lamini­tis af­ter an oral su­gar test. How­ever, if you are con­cerned about giv­ing su­gar to a horse who might have EMS, a rest­ing in­sulin con­cen­tra­tion test can be per­formed in­stead. This in­volves tak­ing a sin­gle sam­ple of blood to mea­sure in­sulin lev­els. A pos­i­tive re­sult will con­firm the di­ag­no­sis, but neg­a­tive re­sults are not con­clu­sive, so ex­perts still rec­om­mend per­form­ing an oral su­gar test if the rest­ing in­sulin con­cen­tra­tion test pro­duces a neg­a­tive re­sult.

In­sulin Tol­er­ance Test: Un­like the oral su­gar test, the in­sulin tol­er­ance test does not re­quire a horse to fast first so can be done spon­ta­neously or on short no­tice. The in­sulin tol­er­ance test is per­formed by draw­ing blood and check­ing a horse’s glu­cose level. The vet­eri­nar­ian then in­jects the horse with a small amount of in­sulin and, af­ter 30 min­utes, draws blood to mea­sure the glu­cose level again. If the blood glu­cose level de­creases by less than 50 per­cent, the horse is con­sid­ered pos­i­tive for in­sulin dys­reg­u­la­tion. A de­crease of blood glu­cose lev­els by more than 50 per­cent is con­sid­ered nor­mal, but your vet may still rec­om­mend an oral su­gar test in or­der to con­firm the horse’s health. Note: There is a small risk of the horse de­vel­op­ing hy­po­glycemia (low blood su­gar) with the in­sulin tol­er­ance test.

Dr. Frank rec­om­mends per­form­ing one of th­ese blood tests an­nu­ally to check your horse’s in­sulin sta­tus, es­pe­cially if he

is be­ing treated for EMS or is a high-risk breed or has a known hered­i­tary con­nec­tion. Test­ing your horse when he re­ceives his spring vac­ci­na­tions is con­ve­nient. This is also when the grass is lush, grow­ing rapidly and con­tains a high su­gar con­tent, so in­sulin dys­reg­u­la­tion is more likely dur­ing this time.

Amanda Adams, PhD, as­so­ciate pro­fes­sor of vet­eri­nary sci­ence at the Uni­ver­sity of Ken­tucky’s Gluck Equine Re­search Cen­ter, agrees: “Don’t guess. Test. Be proac­tive be­fore they’re even metabolic or show­ing signs of obe­sity. Fol­low their insu- lin lev­els over time. It’s a grad­ual change, but it can sneak up on you.”

Dras­tic Man­age­ment Ad­just­ments

If your horse is di­ag­nosed with in­sulin dys­reg­u­la­tion, an im­me­di­ate diet change is re­quired to re­duce the amount of su­gar and car­bo­hy­drates in his diet, which will, in turn, keep his glu­cose lev­els down. How dras­ti­cally you need to change his diet de­pends on the sever­ity of his con­di­tion. The blood tests will in­di­cate where he falls on the spec­trum, but any signs of lamini­tis (a strong digital pulse, dis­torted hoof shape, rings on the hoof wall, short­ened stride, un­usual weight shift­ing, re­luc­tance to walk, vis­i­ble lame­ness) should be con­sid­ered se­ri­ous.

If your horse is di­ag­nosed as se­verely in­sulin-dys­reg­u­lated based on the re­sults of the blood test and is also obese, the Equine En­docrinol­ogy Group cur­rently rec­om­mends start­ing him on an ini­tial hay-based diet and ex­clud­ing grain com­pletely. Re­strict turnout to a dry lot or a small pad­dock with lit­tle grass. Su­gar con­cen­tra­tions in grass are higher in the mid­dle of the day, so con­sider turn­ing him out only at night or in the morn­ing. If he is obese, feed him only 1.5 per­cent of his body weight in hay daily for 30 days. You can spread this hay ra­tion over two or three feed­ing pe­ri­ods per day or put it in a slow-feeder haynet.

Ex­perts rec­om­mended feed­ing EMS horses hay that is low in non­struc­tural car­bo­hy­drates—su­gar and starch. Many fac­tors af­fect the NSC lev­els of hay, so the only way to know for sure is to have it tested. Then con­sult your vet­eri­nar­ian about the re­sults. If you are un­able to test the su­gar lev­els of your hay, soak each of your horse’s hay meals in wa­ter for at least 30 to 60 min­utes, then drain it be­fore feed­ing. This will re­move a sub­stan­tial amount of sug­ars.

“Weigh the horse and weigh the flakes of hay so you

know ex­actly how much you are feed­ing,” Dr. Adams says. “If the horse still hasn’t lost weight af­ter a month, you can start to de­crease this per­cent­age care­fully, but work with a vet/nu­tri­tion­ist to do so safely.”

If, by the end of the 30 days, your horse has suc­cess­fully lost weight, con­tinue the re­stricted diet un­til fol­low-up blood tests in­di­cate a sig­nif­i­cant im­prove­ment.

EMS horses who are not obese or have lost the weight may be main­tained on low-su­gar, low-starch grain and hay. If nec­es­sary, calories may be added with high-qual­ity fiber, such as beet pulp. Some horses may not

need grain at all. In­stead, they can get nec­es­sary vi­ta­mins and min­er­als from supplements or a ra­tion bal­ancer. If your horse must have grain, feed him smaller, more fre­quent meals per day to avoid glu­cose spikes. Restrict­ing a horse’s diet is usu­ally not enough to treat EMS suc­cess­fully. Ex­er­cise is im­por­tant, as well, re­gard­less of the sever­ity of his con­di­tion—es­pe­cially if he is over­weight. In­sulindys reg­u­lated horses have a harder time los­ing weight, so plenty of ex­er­cise is nec­es­sary to pull off those pounds. Dr. Adams says there is no “ex­act” ex­er­cise reg­i­men guar­an­teed to im­prove in­sulin dys­reg­u­la­tion. “It re­ally is some­thing, along with diet, that needs to be tai­lored to the in­di­vid­ual horse.” (If your horse is al­ready suf­fer­ing from lamini­tis, talk to your vet and far­rier about pro­vid­ing ad­di­tional shoe­ing sup­port and ad­dress­ing how and when to ex­er­cise him.)

In some cases, med­i­ca­tion is nec­es­sary to treat EMS. There are two med­i­ca­tions most com­monly used:

■ A high dose of Thyro-L (levothy­rox­ine sodium pow­der) is specif­i­cally used to help obese horses lose weight if they are un­able to do so through nor­mal man­age­ment prac­tices.

■ The sec­ond drug is called met­formin, which is com­monly used to treat di­a­betes in hu­mans. How­ever, Dr. Frank ex­plains, it has mixed re­sults in horses. “It is not ab­sorbed very well, but it is still worth at­tempt­ing to use this as a treat­ment for a horse that is se­verely af­fected and won’t re­spond to man­age­ment prac­tices.”

Life­long Main­te­nance

Un­for­tu­nately, an EMS horse can never be fully cured, but the dis­or­der can be man­aged through proper nu­tri­tion and ex­er­cise. “The key is to rec­og­nize the risk, mit­i­gate the risk and pre­vent them from de­vel­op­ing lamini­tis,” Dr. Frank says.

As is of­ten the case, the best treat­ment is pre­ven­tion. If your horse is at risk for EMS, look out for the phys­i­cal signs and have his blood reg­u­larly tested. If you catch EMS in the early stages, there is no rea­son why he can’t go on to live a healthy, ac­tive life.

Dr. Adams stresses that you don’t have to be in this alone. “Work with your vet­eri­nar­ian, nu­tri­tion­ist, far­rier. It takes that team to help man­age th­ese horses.”

LEFT: A nor­mal hoof. RIGHT: A se­verely laminitic hoof where the sen­si­tive lam­i­nae are in­flamed and the hoof wall and cof­fin bone sep­a­rate, which has caused the bone to painfully ro­tate down­ward.

Be­cause grass is high in su­gar, in­sulin-dys­reg­u­lated horses must have their di­ets care­fully man­aged. Turn­ing them out on a dry lot or fit­ting them with a graz­ing muz­zle can keep su­gar in­take to a min­i­mum.

Horses with lumpy or dim­pled fat pads (such as be­hind the shoul­der, around the tail­head or over the loin) are of­ten pre­dis­posed to metabolic is­sues such as in­sulin re­sis­tance.

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