Amino Acids for Proper Nu­tri­tion

Is your horse get­ting the right amount and type of the body’s build­ing blocks to be healthy and per­form his best?

Practical Horseman - - Contents - By El­iz­a­beth Iliff Prax

Learn about the im­por­tance of amino acids and how to en­sure your horse is get­ting the right amount for his health and per­for­mance.

Amino acids are a hot topic in to­day’s equine nu­tri­tion. They are the vi­tal bi­o­log­i­cal build­ing blocks that link to­gether in the horse’s body to create pro­teins, which form ev­ery­thing from mus­cle tis­sue to or­gan tis­sue as well as en­zymes, hor­mones and an­ti­bod­ies. “Aside from wa­ter, pro­tein is the most abun­dant molecule in the body,” says Mid­dle Ten­nessee State Uni­ver­sity as­so­ciate pro­fes­sor Holly Spooner, PhD. “All tis­sue is made from pro­tein. But it is per­haps the most mis­un­der­stood es­sen­tial nu­tri­ent.”

Horse own­ers tend to fo­cus on crude pro­tein, which, she ex­plains, is ac­tu­ally just an es­ti­mate of the amount of pro­tein in a feed product based on how much ni­tro­gen is present (since ni­tro­gen is much more abun­dant in pro­tein than in other nu­tri­ents). “But that doesn’t ex­actly tell the whole story,” Dr. Spooner says. Qual­ity mat­ters more than quan­tity when it comes to pro­tein in your horse’s diet—and qual­ity is de­ter­mined, in part, by which amino acids are present in his food.

All grasses, grains and hays have a cer­tain amount of pro­tein in them. When it ar­rives in your horse’s stom­ach and small in­tes­tine, en­zymes break it down into its amino-acid com­po­nents. His body then puts these build­ing blocks to­gether in new con­fig­u­ra­tions to make what­ever it needs at the mo­ment—for ex­am­ple, new tis­sue for mus­cles or vi­tal or­gans.

Horses, like all mam­mals, use only about 22 of the more than 500 amino acids that ex­ist on earth. Their bod­ies man­u­fac­ture 12 of those 22, so we need to pro­vide the other 10 “es­sen­tial” amino acids through food: ly­sine, me­thio­n­ine, argi­nine, his­ti­dine, phenyl­ala­nine, thre­o­nine, tryp­to­phan, va­line, leucine and isoleucine.

Each pro­tein a horse’s body makes has a unique code, a for­mula dic­tat- ing how a spe­cific se­quence of amino acids should be strung to­gether. Some pro­teins con­sist of just a few amino acids; oth­ers are chains of thou­sands. If one amino acid in a par­tic­u­lar pro­tein’s for­mula isn’t avail­able, the body can’t sub­sti­tute it with a dif­fer­ent amino acid, so that pro­tein can’t be made.

“It’s like putting to­gether Le­gos,” Dr. Spooner says. “The in­di­vid­ual blocks are like amino acids. If your plan calls for six red Lego blocks and you don’t have six red Le­gos, you can’t keep build­ing. It doesn’t mat­ter that you have 150 blue Le­gos or 200 green Le­gos.”

In this sce­nario, the red Lego rep­re­sents what is known as a “lim­it­ing amino acid.” How much you have of it lim­its how much pro­tein you can build. In horses, sci­en­tists know that ly­sine is the most im­por­tant lim­it­ing amino acid. They’ve es­ti­mated how much ly­sine horses need in their di­ets, but there is very lit­tle re­search about how much of each of the other amino acids they re­quire. This is be­cause horses are more la­bor-in­ten­sive to study and the ben­e­fits are harder to de­fine than in other species, such as pigs and chick­ens.

While we wait for equine sci­ence to catch up, much of what we do know comes from human-nu­tri­tion re­search. For ex­am­ple, as with hu­mans, although amino acids play many dif­fer­ent roles in the horse’s body, their pri­mary pur­pose is to build pro­tein. “Any­thing be­yond that is go­ing to be a rel­a­tively small por­tion of that amino acid,” says Uni­ver­sity of Ken­tucky as­so­ciate pro­fes­sor of equine sci­ence Kris­tine Urschel, PhD. “Peo­ple get bogged down with some of the spe­cial uses for amino acids—such as tryp­to­phan hav­ing a calm­ing ef­fect—when, first and fore­most, amino acids are used to make pro­tein.”

How to Make More Mus­cle

So let’s fo­cus on pro­tein—more specif­i­cally, mus­cle pro­tein. Mus­cle is about 70 per­cent wa­ter and 20 per­cent pro­tein. The other 10 per­cent in­cludes fat, vi­ta­mins, min­er­als and

How to In­ter­pret Feed La­bels

In gen­eral, both our ex­perts agree that most horses get all the pro­tein they need from a com­bi­na­tion of good-qual­ity for­age and a suit­able amount of con­cen­trate de­signed for their age and life­style. How­ever, says Dr. Spooner, the crude pro­tein per­cent­age you see on a feed la­bel “really isn’t what we should be fo­cus­ing our at­ten­tion on. All pro­teins are not cre­ated equal. If we’re meet­ing the horse’s pro­tein re­quire­ment with poor-qual­ity pro­tein in terms of the amino-acid pro­file, we could still have a horse who is un­able to build the pro­tein that he needs.”

So what is good-qual­ity pro­tein? In for­age, it usu­ally means im­ma­ture, leafy hay rather than old, stemmy hay. Grass hays are gen­er­ally be­tween about 6 and 10 per­cent pro­tein, whereas legume hays, like al­falfa and clover, can be 15 per­cent or higher. What­ever hay you’re feed­ing, Dr. Spooner highly rec­om­mends hav­ing sam­ples of it tested “be­cause it can be very de­ceiv­ing. For in­stance, we have a rel­a­tively im­ma­ture prairie-grass hay here at the uni­ver­sity that of­ten comes in with a pro­tein level of 4 to 6 per­cent, which is pretty low com­pared to what most peo­ple might ex­pect.”

To fur­ther com­pli­cate things, re­searchers have learned that horses’ bod­ies can’t ac­tu­ally ac­cess all the pro­tein they re­ceive in for­age. That’s be­cause the plants’ thick cell walls—the fiber—can’t be bro­ken down un­til the for­age ar­rives in the large in­tes­tine, also known as the hindgut. But the en­zymes in charge of break­ing pro­teins down into amino acids are lo­cated in the foregut: the stom­ach and small in­tes­tine. So, the­o­ret­i­cally, by the time the pro­tein from for­age is ac­ces­si­ble, it may be too late for the body to ac­tu­ally use it. Con­cen­trates, on the other hand, have less fiber, so are more eas­ily di­gested in the foregut. “This is an­other area of re­search that is su­per ex­cit­ing,” says Dr. Urschel. “There’s still a ton that we need to know about it. We know that wild horses have been able to sur­vive and re­pro­duce on al­most ex­clu­sive for­age-type di­ets. So it’s a bit of a co­nun­drum. I think horses can get at least some amino acids from a good-qual­ity for­age, but the lower the fiber in the food, the more di­gestible in the foregut the pro­tein is.” Hav­ing said that, though, she is quick to add, “I still strongly be­lieve that for­age should be the back­bone of most di­ets.”

The pro­tein qual­ity in con­cen­trates also de­pends on the source. For ex­am­ple, ce­real grains, such as oats and corn, tend to be low in ly­sine, whereas legumes and oil seeds, such as soy­bean meal, have higher ly­sine lev­els. Com­mer­cial feed com­pa­nies of­ten add pu­ri­fied forms of amino acids di­rectly to their prod­ucts to en­sure that they reach ad­e­quate lev­els. These are more di­gestible be­cause they’re al­ready in free amino-acid form. How­ever, Dr. Urschel says, read feed la­bels care­fully. “If you see, say, leucine in­cluded in the guar­an­teed anal­y­sis, but not in the in­gre­di­ent list, all they’ve es­sen­tially told you is that leucine was con­tained in the grains. They haven’t added any ad­di­tional leucine to it. If it’s in free form, it will be listed sep­a­rately as an in­gre­di­ent.”

The four most com­mon free forms of amino acids that you’ll see in an in­gre­di­ent list are L-ly­sine, L-thre­o­nine, L-tryp­to­phan and DL-me­thio­n­ine. Un­for­tu­nately, un­til more re­search is con­ducted, sci­en­tists still don’t know what horses’ ex­act re­quire­ments are for each of these amino acids. They do be­lieve, how­ever, that these free forms are the eas­i­est for horses’ bod­ies to ac­cess in their di­ges­tive tracts.

An­other way to make the amino acids in your horse’s diet more bioavail­able is to limit the size of his meals. “Horses of­ten have greater di­gestibil­i­ties when a more rea­son­able amount of con­cen­trate is fed at any given time,” says Dr. Spooner. She rec­om­mends keep­ing con­cen­trate meals at or be­low about 0.5 per­cent of your horse’s body weight (so about 5½ pounds of food for a 1,100-pound horse per meal).

Too Much of a Good Thing

Un­til we know ex­actly how much our horses need of each amino acid, why don’t we just give them lots of each? Be­cause the body can’t store amino acids to use later the way it stores car­bo­hy­drates and fat. “The body doesn’t store ex­tra pro­tein as mus­cle,” says Dr. Urschel. In­stead, she ex­plains, the liver con­verts the amino acids that aren’t used im­me­di­ately into a com­pound called urea, which is then passed on to the kid­neys where it’s fil­tered and ex­creted in the urine.

This process re­quires en­ergy and other ad­di­tional re­sources, such as wa­ter. The horse’s body can use pro­tein to pro­duce en­ergy as well, but, as Dr. Spooner says, this is “metabol­i­cally ex­pen­sive. It’s not the eas­i­est way for the horse to make en­ergy.” Be­cause it’s much eas­ier to pro­duce en­ergy from car­bo­hy­drates and fats, ex­cess pro­tein usu­ally goes un­used and thus must be elim­i­nated from the body. This forces the liver and kid­neys to work harder as they have to break down and process the pro­tein. “If you’ve ever known any­one who’s done the [low-carb] Atkins Diet, what they’re do­ing is uti­liz­ing pro­tein (and fat) for en­ergy. It’s been known to make peo­ple grumpy and they don’t feel well, es­pe­cially if they try to ex­er­cise.

“Ex­cess pro­tein may also hin­der per­for­mance in the horse,” she con­tin­ues. “It con­trib­utes to what we call aci­do­sis—a low­er­ing of the pH within the horse’s body—which causes him to fa­tigue faster and not have as good a per­for­mance.” Con­se­quently, in re­cent years, equine nu­tri­tion­ists have be­gun rec­om­mend­ing that per­for­mance horses be fed a lower per­cent­age of di­etary pro­tein to avoid the pro­tein ex­cesses that of­ten ac­com­pany the ex­tra calo­ries they con­sume.

The aci­dotic state caused by ex­cess pro­tein can also in­flu­ence how much cal­cium is ab­sorbed into the gut of young, grow­ing horses. Re­searchers be­lieve this might com­pro­mise bone growth.

Pro­tein is one of the most ex­pen­sive in­gre­di­ents in horse feeds, so feed­ing your horse ex­tra pro­tein is an un­nec­es­sary drain on your bud­get. Be­cause of its high ni­tro­gen con­tent, it’s also a po­ten­tial en­vi­ron­men­tal pol­lu­tant, not just to nearby land and wa­ter but to your horse’s im­me­di­ate sur­round­ings. When horses ex­crete ex­cess pro­tein, it pro­duces am­mo­nia gas—the strong smell we all as­so­ciate with dirty stalls—which, in large quan­ti­ties, can im­pact your horse’s res­pi­ra­tory sys­tem.

Pre­ci­sion Feed­ing

So how can you pro­vide the ben­e­fits of amino acids without risk­ing these down­sides? “There’s a push to­ward what’s called pre­ci­sion horse feed­ing, do­ing a bet­ter job of just meet­ing the re­quire­ments, as op­posed to throw­ing the kitchen sink at them,” says Dr. Spooner.

Although the NRC doesn’t yet of­fer com­pre­hen­sive amino-acid pro­files in its feed­ing guide­lines, re­searchers con­tinue to study horses’ spe­cific di­etary re­quire­ments. For ex­am­ple, a re­cent study found that the amino-acid con­cen­tra­tions in horses’ sweat are dif­fer­ent from those in their blood­streams. They also have a spe­cial pro­tein in their sweat that hu­mans don’t have, called lath­erin, which forms the white lather you see on their coats when they ex­er­cise stren­u­ously. This plays an im­por­tant role in keep­ing the sweat on the horse’s hair, rather than drip­ping off his body, thus al­low­ing it to most ef­fec­tively cool him via evap­o­ra­tion.

The re­searchers of this study de­vel­oped a feed sup­ple­ment to ad­dress the unique amino-acid con­cen­tra­tions they’d mea­sured in horses’ sweat. Their results are still pre­lim­i­nary, but anec­do­tal ev­i­dence looks promising. Since horses lose sig­nif­i­cantly more amino acids through sweat than hu­mans do, this is one area where equine-spe­cific stud­ies will be in­valu­able.

While the sci­ence evolves, both of our ex­perts cau­tion horse own­ers to be wary of com­mer­cial prod­ucts’ claims that aren’t sub­stan­ti­ated with widely pub­lished, im­par­tially ob­tained data. For ex­am­ple, says Dr. Spooner, “There’s a fairly com­mon be­lief that horses that look poor in their toplines can ben­e­fit from amino-acid sup­ple­ments. But you have to go back and say, ‘Well, what else is be­ing done? Did you put that horse into work? Did you sud­denly feed him more in gen­eral and maybe what he really needed was just more en­ergy?’ I think the jury’s still out on that to some ex­tent.”

Un­til we have bet­ter sci­ence, our ex­perts agree, there’s no harm in ex­per­i­ment­ing with com­mer­cial amino-acid prod­ucts, for ex­am­ple, with a horse who ap­pears to be re­ceiv­ing an ad­e­quate num­ber of calo­ries and the cor­rect type of train­ing to build a good topline but still isn’t do­ing so. If you de­cide to sup­ple- ment your horse’s diet with one of these top dress­ings, Dr. Urschel rec­om­mends fol­low­ing the por­tion guide­lines closely and giv­ing it at least a two-month trial. If you don’t no­tice an ob­vi­ous change af­ter two months, your horse was likely al­ready re­ceiv­ing all the amino acids he needed in his reg­u­lar diet.

Re­searchers have re­cently dis­cov­ered that horses have a spe­cial pro­tein in their sweat called lath­erin, which forms the white lather on their coats when they ex­er­cise stren­u­ously. This keeps the sweat on the horse’s hair, rather than drip­ping off, and...

Even if you see com­mon free forms of amino acids, such as L-ly­sine, L-thre­o­nine and DL-me­thio­n­ine, on a grain bag la­bel’s guar­an­teed anal­y­sis, it doesn’t mean they were added in as sep­a­rate in­gre­di­ents.

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