Big Appetites In Big Horses (Drafts)
- Sep 13, 2001
Nothing says sheer power like a draft horse. Nothing else exudes such strength with such a mild-mannered attitude. To watch these gentle giants in action is to get a sense of our own history and the invaluable role horses played, and continue to play. Today, far from fading away, the draft breeds--Clydesdales and Shires, Percherons and Belgians (not to mention all the other, more obscure varieties, like Brabants, Suffolk Punches, and American Creams)--are more popular than ever, and attracting more converts every year.
In most respects, very little about the management of draft horses has changed over the centuries. That's true not only of the harness they wear, and the vehicles they pull--essentially identical to those used at the dawn of the Industrial Revolution--but also in the diets we tend to offer the draft breeds. Tradition plays a larger role in the care and feeding of heavy horses than in most other realms of the equine industry, mostly because keeping and enjoying these breeds often is passed down through generations of family. "If it was good enough for great-great-grandpappy's horses, it's good enough for mine!" isn't an uncommon attitude among draft aficionados. While there's nothing wrong with that, it does mean many draft horses could be benefiting from more advanced (or at least more balanced) nutrition than they currently enjoy. Sturdy and stoic by nature, they'd be the last to complain of being fed inappropriately; but nonetheless, many a heavy horse's diet could be updated, particularly in light of some recent discoveries about carbohydrate utilization in these breeds.
Strength and power are the draft horse's forte, and his heavy bone and extensive muscling reflect those requirements, resulting in an animal which often tops the 2,000-pound mark. These days, the demands of the show ring have resulted in two distinct types of horses in many of the heavy breeds--a taller, flashier animal for the show hitches, and a less rangy, more rugged individual for "real" pulling work. Both types, however, have significant energy requirements for performing the work they're asked to do.
The easy-going temperament and laid-back metabolism of most heavy horses is largely responsible for the fact that they seem to require about 15% fewer calories, pound for pound, than a light horse breed. Studies have worked out the difference to be approximately 1.27 Mcal/100 pounds of body weight for a draft horse, versus 1.48 Mcal/100 pounds for a Thoroughbred or Arabian, for example. Still, that's a lot of feed, especially if you're used to feeding smaller horses. Many draft equines easily consume a bale of hay, or more, per day, and many also are fed large amounts of plain grains, such as oats and bran. (Even draft crosses, which are popular for foxhunting, eventing, light farm work, and many other uses, often range upwards of 1,600 pounds and can have prodigious appetites to match.)
In the past, bran was an extremely popular feed for draft horses; some owners still maintain an affection for feeding it today. Because bran has an extremely inverted calcium:phosphorus ratio, containing about 13 times as much phosphorus as calcium, it can, if fed in large quantities, contribute to calcium deficiency. For good bone growth and maintenance, the horse's system requires at least as much calcium as phosphorus in the overall diet (the ratio is more important than the actual quantities of each mineral). When faced with a phosphorus overload, the body actually will leach calcium from the bones in an attempt to rebalance the two minerals. The eventual result is porous, brittle bones throughout the body--and curiously, the bones of the head become visibly enlarged as their calcium is replaced with fibrous connective tissue, hence the name "big head disease" (also called "bran disease"). While big head disease is rare today, the draft horses of a century ago were quite likely to suffer from it. Its effects were usually irreversible, severely shortening the useful life of the animal.
Bran is a less-than-ideal feed for other reasons, too. It's not particularly energy-rich, it doesn't really produce the laxative effect it's fabled for, and as a fiber source, it's only fair. An occasional bran mash on a cold winter's night does no harm, and certainly might stimulate the appetite of a convalescing horse, but if you must feed bran on a regular basis, try to make it no more than 10% of the overall diet.
Most of the work done by the draft breeds is aerobic in nature--in other words, slow and steady, and of long duration. Horses used for pulling contests, and those employed in real farm work, sometimes have to employ anaerobic energy metabolism, too, for occasional short bursts of extreme effort. The snag is that heavily muscled horses (which pretty much describes all the draft breeds) are particularly prone to tying-up, also known as exertional rhabdomyolysis, azoturia, or "Monday morning disease." The latter name came about because, back in the days when all draft horses worked hard for a living, they often would be fed full grain rations through the weekend when they were idle. Then when they returned to heavy work on Monday morning, their hindquarter muscles would cramp and seize, and they'd become painfully rooted to the spot. (The condition also used to be called "blackwater," because a horse which had tied up later would expel urine that was so full of pigments from damaged muscle cells that it appeared bloody or coffee-colored--a condition called myoglobinuria.)
Although tying-up isn't exclusive to the draft breeds by any means, it's long been noted that heavy horses have a tendency to suffer from it. Reducing the amount of carbohydrate-rich grain fed on non-working days appears to help control the incidence of tying-up episodes--sometimes. Many suspect that exertional rhabdomyolysis has a genetic component, as is evidenced not only by its prevalence in draft horses, but also its prevalence in fillies and mares of other breeds.
Many draft horses suffer from other types of muscle disorders, ranging from barely perceptible to downright alarming. "Shivers," a condition in which the horse trembles or quivers and the tail is elevated abnormally, is one, as is a slightly "crampy" way of moving behind (this is widespread enough that many consider it "normal" for a draft horse). Stringhalt--a chronic syndrome in which the horse suddenly snatches up his hind legs (one or both might be affected)--often is seen in heavy horses and can progress to muscle wasting and general weakness.
Worst of all is the down horse--an animal which suddenly finds himself devastatingly weak and unable to stand. This syndrome particularly is common after foaling or following general anesthesia (draft horses are notorious in veterinary hospitals for having problems associated with general anesthesia), but it also can strike apparently healthy horses without warning; and it might necessitate euthanasia.
Loss of muscle mass in the shoulders and/or hindquarters, refusing to pick up the feet for shoeing, stumbling or a reluctance to back up, difficulty rising after recumbency, stiff or awkward hind limb movements or short-stridedness, episodic colic, back soreness, and a general lack of energy -- all of these can be indications of a lack of muscle energy, according to Beth Valentine, DVM, PhD, of Oregon State University. A veterinary pathologist, Valentine stumbled across some mysterious similarities in slides of muscle cells taken from draft horses brought in for necropsy while she was based at Cornell University about five years ago. Drawing comparisons from work in Quarter Horses suffering from tying-up and hyperkalemic periodic paralysis (HYPP), she began to gather data on the muscle disorders from which these horses suffered, and soon suspected not only that there was a common link, but that what she was witnessing was a cellular indication of the horses' poor utilization of carbohydrates for energy.
In essence, the body ended up "starving" the muscles, as it was unable to process grain as an energy source. She dubbed the syndrome equine polysaccharide storage myopathy (EPSM), and has been investigating it ever since.
"I started out thinking this is an oddball little condition," says Valentine, "but when I started looking, it was easy to find these horses (with EPSM). Often they didn't tie up -- we usually see full-blown tying-up only with draft horses used for heavy pulling. The symptoms would be fairly mild and easy to miss. They often were attributed to just Ôbeing a draft horse.' A draft horse, after all, doesn't tend to kick up his heels in the pasture the way a lighter horse might. But I started to think that perhaps this was because he was hurting! The horse who's a little stiff or short behind, the one who doesn't want to hold his feet up for the farrier, the one who doesn't like to be curried around his back legs -- all of these small signs started to point to muscle weakness and pain."
She started to do muscle biopsies on draft horses brought in to the university for necropsy, and was surprised to find that the muscle lesions she'd observed were apparent in at least half of the samples she examined. Its incidence ran the gamut from Clydesdales, Shires, Percherons, and Belgians, to Irish Draughts and draft ponies such as Haflingers and Fjords, several draft crosses, and even a draft mule.
While EPSM doesn't appear to be limited to the draft breeds, it seems to be disturbingly common in heavy horses, according to Valentine. She notes, "Even if the population I've sampled is somehow skewed, even if the incidence is only half of what I suspect it is, that's still one in four horses! I'm quite sure it's genetic, but with this many horses affected, breeding it out isn't the answer. In fact, we may have unintentionally selected for EPSM while we were selecting for other desirable traits. Interestingly, the majority of horses who have tested positive for the syndrome are otherwise exceptional athletes."
Why hasn't EPSM been identified until now? Valentine suspects that the symptoms have been obscure enough, and the horses stoic enough, that it has been difficult to put the pieces together. "These horses won't let you know when there's a problem as quickly as a light horse would. They'll work till they drop. Often you don't know there's anything going on until the horse suffers severe and rapid muscle wasting. He may look fine until he's 20 years old, then suddenly goes downhill. Or he may manifest problems from the time he's two. It's tremendously variable.
"EPSM is out there, and these horses are trying to deal with it. I thought that because Quarter Horses who tied up chronically seemed to respond to low-carbohydrate, high-fat diets, that a low-carb diet might also be of assistance (for EPSM horses)."
RX For EPSM horses
In consultation with equine nutritionists Arleigh Reynolds, Harold Hintz, and Kent Thompson, among others, Valentine came up with a proposed diet for EPSM horses that featured little or no carbohydrates from grains, and 20% to 25% fat, which served as a substitute energy source. Although fat is not a "natural" part of the equine diet, horses actually process it very well, and their bodies readily utilize it as an energy source, albeit exclusively for aerobic work (its components, called volatile fatty acids, or VFAs, won't fuel anaerobic, or "sprint" muscle firing).
"We don't have any true information yet on the level of carbohydrates these horses can tolerate," Valentine notes, "so we're trying to go for zero carbs. And 20% fat seems to be the minimum for good results, according to my observations."
Since EPSM horses don't seem to have any trouble processing fiber, Valentine's experimental diet still includes plenty of forage and/or hay.
For the average draft horse, providing the low-carb, high-fat diet is relatively simple. Valentine recommends replacing the horse's normal grain ration with alfalfa pellets and vegetable oil (gradually brought up to a level of three to four cups for a 1,600- to 2,000-pound horse). Any good-quality vegetable oil can be used, although she suggests avoiding linseed (flax) oil because some studies suggest it could contribute to colic when fed in large quantities. Corn, soy, or canola oil can be purchased in bulk from your feed store or from a restaurant supply, she says, and since you are feeding fairly large amounts, rancidity is rarely a problem -- the oil doesn't sit around long enough!
While owners might find this diet rather messy ("I've learned to designate one jacket for barn use," Valentine says wryly.), most horses adapt to it remarkably well. Valentine has noted more objections to the alfalfa pellets than to the oil itself; some horses do turn up their noses at the processed hay, and for those she suggests trying a low-carbohydrate, high-fiber feed such as Purina's Strategy or Nutrena Compete, or simply pouring the oil directly on the horse's flakes of hay. (Beet pulp might be another potential solution, although Valentine suspects its soluble carbohydrate content could be a little high.) If your horse objects to liquid oil, there are a couple of alternatives on the market -- rice bran, for example, and high-fat supplements such as Purina's Athlete. Since these products are only about 14% to 22% fat, considerably more must be fed in order to achieve the overall dietary balance of 20% to 25% fat. (For example, a 2,000-pound draft horse would need to consume 10 pounds of rice bran a day!) As a result, you might run into palatability problems.
Some owners have found that combining these products does the trick. There also is a powdered animal fat product called Fat Pak 100, which is primarily designed for pigs, but which can be fed safely to horses. (Avoid the rumen-protectant varieties of fat designed for ruminants like cattle and sheep; they can be toxic to horses.)
If the fat is added gradually to the diet, horses tend to adapt to it extremely well and rarely experience diarrhea or other signs of digestive difficulties, says Valentine. (An energy-starved EPSM horse will tend to absorb the fat very efficiently in the small intestine, so little or none of the fat ever reaches the large intestine to contribute to loose manure.) While a diet this high in fat probably will not be any cheaper than a normal, grain-based ration, it shouldn't cost you significantly more because fat actually is far more energy-dense than a comparable quantity of carbohydrates. Four cups of oil (approximately two pounds) provide about 8,000 calories, while two pounds of corn, oats, or commercial sweet feed provide only 2,400 to 2,800 calories. "Factor in the potential costs of veterinary care for an EPSM-affected horse, or even the loss of a horse," says Valentine, "and the cost of the new diet looks even better."
There are a couple of other minor dietary considerations for EPSM horses. First, because they are not receiving the benefit of the other nutrients that grains provide (primarily trace minerals and vitamin E), it might be beneficial to feed a good-quality vitamin/mineral supplement, and some added vitamin E and selenium. Second, because Valentine suspects these horses have to effect some muscle repair over and above the norm, she suggests a slightly higher level of protein in the diet than the average adult horse needs. (This requirement normally is adequately met by the alfalfa pellets, which might be up to 20% crude protein.) Exercise plays a role in the management of an EPSM horse. Daily turnout and regular work seem to help such an animal avoid muscle stiffness and maintain a baseline of fitness, which will stand him in good stead when his work requirements increase.
Results Of Diet Therapy
Valentine has noted dramatic improvements in almost all of 250 suspected EPSM horses placed on this low-carb, high-fat diet (67% of which were draft horses, Quarter Horses, or heavily muscled warmbloods). More than 90% of horses which previously exhibited tying-up, gait abnormalities, muscle atrophy, pelvic limb weaknesses, and episodic colics have responded positively to the diet therapy, she reports, with cases of stringhalt and/or shivers somewhat less successful (she notes 86% showed some improvement, but that there rarely was a complete cure).
One of the more difficult problems to correct, in Valentine's experience, is generating a correct canter. Many EPSM horses, because of their hind-end stiffness, canter awkwardly and might need time and patient schooling to improve.
As is the case with many diseases, EPSM seems to respond best to the therapy when symptoms are caught early. Severely affected horses do not always respond, Valentine says. Early on in her studies, six draft horses which already were in the advanced stages of the disease died despite dietary changes. In many cases, however, changing the diet of a draft horse from carbohydrate-based to high-fat, low-carbs might decrease, delay, or even prevent the symptoms of EPSM; for some, it has been life-saving.
Dietary therapy doesn't have instant results. Valentine has noted a period of three to four months in which the horse's body seems gradually to adapt to the availability of fat as an energy source. During that time, symptoms might get worse before they get better. Severely affected EPSM horses can go through a number of ups and downs, health-wise, in that time. "It's a real nightmare," she says. The important thing is to persevere and stick to the diet; reducing the amount of fat for your own convenience will result in no benefit for your horse.
Provided you ride out those potentially rocky first four months, the change in your horse might be remarkable, according to Valentine. "I have seen the difference in these horses. So many of them just didn't look happy -- and four months later they definitely look more content. They have more energy, they run and play in the pasture, they sometimes feel so good they're bouncing off the walls! I can't do any science on that, but I have videotape after videotape which demonstrates it." Some of the more traditional draft horse owners can be difficult to persuade at first, she adds, but, "when they start to see results, that's convincing!"
At the moment, doing a muscle biopsy (taking a small sample of muscle tissue from the hindquarters, with the aid of a local anesthetic and sedation) is the best way to definitively diagnose EPSM. (Muscle enzyme levels in the blood might be slightly elevated in EPSM horses, but they also can show completely normal levels, so it's not an accurate diagnostic.)
Because the suspected incidence of the disease in draft horses is so high, many owners who notice symptoms prefer to forego this test and try the dietary therapy. If the horse responds positively within about six months, a diagnosis -- in essence -- has been made. In fact, the low-carbohydrate, high-fat diet will do no harm to a "normal" horse, and actually can be beneficial. For example, burning fats for energy is a more efficient process than burning carbohydrates, so the horse on a high-fat diet generates less excess body heat (an advantage which endurance riders and eventers are well aware and use to their benefit when competing in heat and humidity). The potential benefits of the diet are so convincing that Valentine comments, "I'm looking forward to the day that all horse feeds are high-fat and low-carbohydrate diets."
Because an EPSM horse's muscles are starved for energy, it's not sufficient just to provide him with forage (unless he is completely idle). He must not only avoid carbohydrates, but he must take in enough fat to provide his muscles with the fuel they need. Once on the diet and benefiting from its effects, he must remain on the ration for life; if you reduce the fat levels, symptoms will recur, says Valentine.
Although originally EPSM was suspected to be the result of a genetic defect, Valentine remarks that the evidence for that is now somewhat murkier. "Based on similar syndromes in other species, we expected to find a defect in a particular enzyme pathway, but it doesn't seem to be there. Now we're looking at glucose uptake rates, to see whether that has a bearing on why these horses don't seem to be able to utilize carbohydrates."
At some level, all horses are poorly adapted to digesting and using carbohydrates, she notes. It might be that EPSM horses just demonstrate that more dramatically than others.
Are All Cases Of Tying-Up The Result Of EPSM?
Equine polysaccharide storage myopathy (EPSM) can occur in up to 50% of the draft horse population, but it also can occur in other breeds. When it has been diagnosed in light horse breeds, it’s very likely to be associated with horses which suffer from chronic episodes of tying-up.
Is EPSM at the root of all cases of tying-up? It’s too soon to tell, although Valentine thinks it’s possible. "The majority of horses who tie up do respond to a high-fat, low-carbohydrate diet, although it has to be that 20% to 25% level of fat." She also notes that every horse she has studied who has problems with tying-up has so far been biopsy-positive for EPSM.
About the Author
Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.
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