EQUUS - - Answers -


a., b. and pos­si­bly c. Vi­ta­mins E and A are fat-sol­u­ble, which means that a horse who con­sumes more than he needs can store the ex­cess in his liver and other fatty tis­sues. Both are also abun­dant in green, grow­ing grasses but di­min­ish as the plants ma­ture and die. A horse who grazes pas­ture even for just a few weeks a year will be able to store enough to get through the win­ter on dried for­ages. On the other hand, a horse who is fed ex­clu­sively on hay or other forms of dried for­age year-round may need a supplement with vi­ta­mins A and E.

Vi­ta­min E is a po­tent an­tiox­i­dant that helps to limit the dam­age caused by ex­ces­sive free rad­i­cals, elec­tri­cally un­sta­ble mol­e­cules that are a byprod­uct of me­tab­o­lism. When free rad­i­cals are pro­duced in large num­bers, such as in the mus­cles of a work­ing horse, vi­ta­min E helps min­i­mize the ox­ida­tive dam­age to his cells. In ad­di­tion to horses kept pri­mar­ily on hay, hard­work­ing ath­letes, breed­ing mares and stal­lions, and horses prone to ty­ing up may ben­e­fit from sup­ple­men­tal vi­ta­min E.

Vi­ta­min A com­bines with com­pounds in a horse’s retina to play a crit­i­cal role in night vi­sion, and it is also in­volved in body func­tions in­clud­ing re­pro­duc­tion, bone and mus­cle growth, and re­gen­er­a­tion of skin tis­sue. Horses do not con­sume vi­ta­min A di­rectly; rather, they con­sume pre­cur­sor com­pounds, pri­mar­ily beta carotene, that are me­tab­o­lized into the nec­es­sary vi­ta­min com­pounds in the in­tes­tine and liver. Beta carotene is abun­dant in yel­low veg­eta­bles, such as car­rots, as well as green grass and al­falfa.

Vi­ta­min B1 (thi­amine) is nec­es­sary for the me­tab­o­lism of car­bo­hy­drates, and it is found in grains as well as fresh and dried for­ages. How­ever, it de­grades with time in stored hays. Thi­amine is also pro­duced by mi­croflora in the gas­troin­testi­nal tract but not in high enough quan­ti­ties to meet all of the horse’s needs. Thi­amine de­fi­ciency is rare in horses, but it can hap­pen, es­pe­cially in cases where in­testi­nal dis­ease, par­a­site dam­age or the con­sump­tion of toxic plants, such as bracken fern, in­ter­feres with B1 pro­duc­tion.


a. Bi­otin, for­merly called vi­ta­min H, aids in the me­tab­o­lism of fatty acids, pro­teins and car­bo­hy­drates and is es­sen­tial for the cre­ation of new cells within the body. Bi­otin is avail­able from sev­eral com­mon feed­stuffs, in­clud­ing al­falfa and oats, but horses can syn­the­size all that they need within the gut, and de­fi­cien­cies have never been re­ported in horses.

That said, stud­ies have shown that adding a bi­otin supplement of 10 to 20 mil­ligrams per day to a horse’s diet for at least six to nine months can im­prove his hoof qual­ity. The ef­fects of bi­otin sup­ple­men­ta­tion have been con­firmed by ob­serv­ing the changes in the struc­ture of hoof wall with an elec­tron mi­cro­scope, but re­searchers are not sure ex­actly how higher lev­els of bi­otin in the blood af­fect hoof growth. (Bi­otin sup­ple­ments im­prove the growth of new horn; it does not af­fect hoof wall that al­ready ex­ists, so it takes the bet­ter part of a year or more for the new, health­ier hoof wall to grow in.) Con­trary to pop­u­lar be­lief, horses with weak, shelly hoof wall are not de­fi­cient in bi­otin---they have about the same con­cen­tra­tions as other horses. Niacin, pan­tothenic acid

fo­late and (also known as folic acid) are all B vi­ta­mins. Niacin (B3) and pan­tothenic acid (B5) are both widely avail­able in equine food­stuffs, and both are also man­u­fac­tured in the gut in suf­fi­cient quan­ti­ties. Each plays an es­sen­tial role in me­tab­o­lism.

Fo­late (B9) plays a role in the for­ma­tion and growth of new cells. In hu­man medicine, fo­late de­fi­cien­cies may re­sult in birth de­fects, so preg­nant women are of­ten given sup­ple­ments---and so it is of­ten in­cluded in sup­ple­ments for preg­nant mares, too. Green grass is rich in fo­late, how­ever, and the mi­cronu­tri­ent is also syn­the­sized in the equine gut, so nat­u­ral de­fi­cien­cies in horses are rare.


b. Phos­pho­rus and calcium are the two most abun­dant min­er­als in your horse’s body. Calcium makes up about 35 per­cent of his skele­ton, and the min­eral also plays crit­i­cal roles in many func­tions, such as mus­cle con­trac­tion and reg­u­lat­ing the heart rate. Phos­pho­rus is an­other ma­jor com­po­nent of bone, mak­ing

up about 14 to 17 per­cent of the skele­ton, and it also aids the me­tab­o­lism of nu­tri­ents and the uti­liza­tion of vi­ta­mins. Hay and grasses are good sources of both min­er­als; al­falfa is an es­pe­cially rich source of calcium.

Horses re­quire both of these min­er­als in their diet, but it is also im­por­tant to bal­ance the calcium:phos­pho­rus ra­tio. That is, the amount of calcium in a horse’s diet needs to at least meet (a 1:1 ra­tio) or ex­ceed the amount of phos­pho­rus---a ra­tio of 2:1 is con­sid­ered ideal, but most adult horses can tol­er­ate higher amounts of calcium. When the ra­tio is in­verted, how­ever, the ex­cess phos­pho­rus in­hibits the ab­sorp­tion of calcium, and the horse’s body may be­gin to pull calcium out of the skele­ton for other es­sen­tial func­tions. Over time this may weaken his bones and lead to skele­tal de­for­mi­ties.

Grains such as corn, bar­ley or oats (1:15 or more) and wheat or rice bran (1:8) con­tain much higher lev­els of phos­pho­rus than calcium. If these foods form the bulk of a horse’s diet, over time he may ex­pe­ri­ence se­ri­ous health is­sues stem­ming from a lack of calcium. The oc­ca­sional bran mash will not hurt a horse, as­sum­ing he re­ceives an over­all bal­anced ra­tion, but any abrupt change in diet can lead to gas­troin­testi­nal up­set. The safest way to feed a mash is to use his reg­u­lar grain as the base: Sim­ply add enough hot wa­ter to soften it.

Cop­per con­trib­utes to bone for­ma­tion, im­mu­nity and the health of elas­tic con­nec­tive tis­sues. Zinc is a com­po­nent of more than 100 en­zymes and plays a role in the me­tab­o­lism of pro­teins and car­bo­hy­drates. Adult horses usu­ally get an ad­e­quate sup­ply of both from a diet based on for­ages and com­mer­cial feeds. De­fi­cien­cies and/or im­bal­ances of these min­er­als play a role in de­vel­op­men­tal0 ortho­pe­dic dis­ease in foals, but com­mer­cial feeds for­mu­lated for preg­nant mares and grow­ing young­sters will of­fer ad­e­quate, bal­anced amounts of these min­er­als.


d. In ad­di­tion to he­mo­glo­bin, iron is an es­sen­tial com­po­nent of myo­globin, a pro­tein that aids the stor­age of oxy­gen in mus­cle cells, as well as other mol­e­cules in­volved in the trans­port and stor­age of oxy­gen through­out the body.

Ad­e­quate amounts of iron are present in most feeds and for­ages horses eat, and a horse can store iron re­serves in his liver, spleen and bone mar­row that he can draw upon when needed, so nat­u­ral de­fi­cien­cies are rare at any stage of a horse’s life, no mat­ter how hard he works. De­fi­cien­cies can oc­cur, though, in horses who have had se­vere blood loss or ex­ten­sive par­a­site dam­age.

Cobalt is nec­es­sary to the syn­the­sis of vi­ta­min B12, which in turn works to­gether with iron and cop­per to help form new red blood cells. Io­dine sup­ports the func­tion of the thy­roid gland and plays a role in the syn­the­sis of thy­roid hormones that gov­ern me­tab­o­lism. Man­ganese plays a role in the me­tab­o­lism of car­bo­hy­drates and fats as well as the for­ma­tion of car­ti­lage.

All of these min­er­als are present in feeds and for­ages, and de­fi­cien­cies are un­com­mon. In ad­di­tion, iodized salt blocks sup­ply horses with needed io­dine. Tox­i­c­ity from over­doses of these min­er­als are also rare, but con­sum­ing ex­tremely high amounts of these el­e­ments may in­ter­fere with the ab­sorp­tion of other min­er­als.


b. Sodium and chlo­ride are the two com­po­nents of ta­ble salt. Nei­ther are nat­u­rally abun­dant in a horse’s usual food sources, but horses have a nat­u­ral ap­petite for salt and will con­sume what they need from ei­ther a salt block or when of­fered loose salt. Free ac­cess to a source of salt is es­sen­tial year­round but es­pe­cially in hot­ter weather when a horse is los­ing elec­trolytes faster through sweat.

Elec­trolyte sup­ple­ments can help horses re­plen­ish their stores of these min­er­als and re­cover faster af­ter sweat­ing heav­ily. Ath­letes such as en­durance or event horses are ob­vi­ous can­di­dates for elec­trolyte sup­ple­ments when work­ing on hot days, but any horse who sweats ex­ten­sively for at least an hour or two with­out an op­por­tu­nity to eat or drink may also ben­e­fit. This may in­clude the week­end war­rior af­ter an ex­tended ride as well as the fret­ful trav­eler com­ing off of a trailer. Elec­trolytes can be ad­min­is­tered as a top dress­ing, an oral gel or paste, or dis­solved in wa­ter. How­ever you ad­min­is­ter elec­trolytes, al­ways make sure the horse also has ac­cess to plenty of clean, fresh wa­ter.


c. Se­le­nium works in con­cert with vi­ta­min E to act as an an­tiox­i­dant to pro­tect cells from ox­ida­tive dam­age. It also plays a role in the me­tab­o­lism of thy­roid hormones. Se­le­nium de­fi­cien­cies can cause prob­lems with im­mu­nity and re­pro­duc­tion as well as white mus­cle dis­ease. Horses re­quire only a fairly small amount--typ­i­cally about 0.1 mg/kg of their ra­tion or about 0.1 parts per mil­lion (ppm) of their to­tal diet.

Se­le­nium is nat­u­rally oc­cur­ring in hays and pas­ture

grasses, but the amount the plants draw up de­pends on con­cen­tra­tions of the min­eral in the soil. Hays grown in cer­tain re­gions of the coun­try---the Pa­cific North­west, the up­per Mid­west, New Eng­land and the East Coast down to Florida---may be low in se­le­nium, so most com­mer­cial feed mixes in­clude the min­eral in ad­e­quate amounts.

How­ever, too much se­le­nium---as lit­tle as 3 to 5 ppm---can be toxic, pro­duc­ing signs such as a sparse mane and tail, a dull coat, weak and brit­tle hooves, neu­ro­log­i­cal is­sues, and other signs. Soils in some parts of Colorado, Montana, Wy­oming and the Dako­tas may con­tain el­e­vated amounts of the min­eral. The worst cul­prits are cer­tain plants called “se­le­nium ac­cu­mu­la­tors,” which con­tain un­usu­ally high amounts. How­ever, these plants tend to be un­palat­able, so cases of tox­i­c­ity tend to be lim­ited to horses in over­grazed pas­tures who do not have ac­cess to enough high-qual­ity for­age.

Your vet­eri­nar­ian or local ex­ten­sion agent can ad­vise you about se­le­nium in your re­gion. The other con­cern is in feeds and sup­ple­ments. If you’re feed­ing your horse a se­le­nium-rich hay along with a bal­anced com­mer­cial feed plus mul­ti­ple sup­ple­ments, all of which also con­tain se­le­nium, he may be get­ting too much. Your vet­eri­nar­ian or an equine nutri­tion­ist can ad­vise you on an ap­pro­pri­ate feed­ing reg­i­men for your horse.

Potas­sium plays a role in reg­u­lat­ing the fluid bal­ances in cells as well as mus­cle func­tion and the trans­mis­sion in potas­sium, so de­fi­cien­cies are rare in horses with a diet based on hays or grasses.

Sul­fur is a com­po­nent of hoof and hair, and it also makes up part of key amino acids, B vi­ta­mins, in­sulin and chon­droitin sul­fate. Horses are able to get the sul­fur they need from plants, and de­fi­cien­cies are un­known.

Mag­ne­sium is an im­por­tant el­e­ment found in the skele­ton and mus­cle tis­sue, and it plays a role in car­ti­lage for­ma­tion and other func­tions around the body. It, too, is com­mon in plants and com­mer­cial feeds, and de­fi­ciency is rare.

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