Vitamin E

Posted on by — 2 Comments

Written By Dr. Kris Hiney

We have already discussed two of the fat soluble vitamins in a horse’s diet. This month we continue with a closer look at vitamin E, a vitamin which is commonly supplemented to horses for a variety of reasons.  It is often used for aging horses, horses which have muscle disorders and horses which undergo strenuous exercise.  But how do you know if your own horse needs more vitamin E in its diet?

First, let’s explore the role of vitamin E in your horse’s body.  Vitamin E occurs in a variety of forms (both tocopherols and tocotrienols).  Of these, there are then four subgroups, α, γ, β and δ. While γ is the most common in the natural diet, the alpha form is the most potent in activity, the most supplemented and the subject of most studies.   In their natural diet, horses receive the most vitamin E as γ tocopherol from growing forages or harvested forage that was cut at an immature state.  As the plant ages, vitamin E decreases in content.  Vitamin E concentration also decays over time in harvested forages, as much as 50% over one month.  Therefore, older hays which have been stored for some time will have little activity.  If you also feed non-processed concentrates  to your horse (such as oats, barley, corn etc.) they will also be low in vitamin E. However, most commercial equine feeds will be supplemented vitamin E, usually as α tocopherol acetate.   It can be provided as either natural α tocopherol or synthetic, with natural forms having 36% more biological activity than synthetic.  The natural form has been shown to increase plasma α tocopherol concenrations greater than its synthetic counterpart but both are effective supplements.

(This is the structure of alpha tocopherol.)

Despite its form, vitamin E’s function is most frequently thought of as an anti-oxidant.  Vitamin E can work to eliminate free radicals which are formed through the incomplete oxidation of oxygen or other molecules.  During normal metabolism some amount of free radicals are always formed.  However, stress, work, aging, poor nutrition etc can increase the amount of free radicals in the body.  These are essentially molecules which are missing an electron, making  them highly reactive.   This is an unstable condition and the free radical can remove electrons from other cell components, such as lipids, cell membranes etc.  Vitamin E, along with other anti-oxidants donates an electron to the free radical, thus stabilizing it and preventing further damage.  One oxidized, vitamin E itself must be reduced back to its active form.  This is usually accomplished through the action of other anti-oxidants in the body such as ascorbic acid or glutathione peroxidase.  As the cells of the immune system have a high amount of polyunsaturated fatty acids which are quite susceptible to damage by free radicals, vitamin E plays a vital role in the optimization of the immune system.  Furthermore, vitamin E plays a role in reproduction, gene transcription and platelet aggregation.

(Traditional concentrates such as just corn and oats may be relatively low in vitamin E content.)

Currently, vitamin E is recommended to be fed to maintenance horses and breeding horses at 1 IU/kg of body weight (not sure if your horse is a maintenance horse, see Energy Requirements).  Growing horses  and lactating mares are suggested to need more vitamin E in their diet, at double the rate of maintenance horses or 2 IU/kg body weight.  Vitamin E intake for the working horse may need to be a bit higher.  While the current recommendation for working horses is 1.8 IU/kg body weight for moderate work and 2 IU per kg body weight for heavy work, many research studies have provided Vitamin E at higher levels.  Supplementation rates from 150-250 IU/kg DM, 300 IU /kg DM or even as high as 11.1 IU kg/body weight (in a simulated endurance race) have been found to be necessary to maintain blood and muscle concentration of vitamin E in more rigorously exercised horses.  To make these values seem more familiar, if we assume we are feeding a 500 kg horse 2% of its body weight, than the range of vitamin E would be between 1500 – 5500 IU of vitamin E per day in these studies.

Therefore, Vitamin E is often part of the suggested management protocols for horses which are heavily exercising or may have muscle disorders. In fact, in a study looking at endurance horses and supplementation of Vitamin E, the authors were unable to create a control group as no riders were willing to not supplement their horses!  However,i t has been difficult to prove the effectiveness of supplementation for the enhancement of the horse’s health.  In exercised horses receiving 300 IU/kg DM of vitamin E compared to 80 IU/kg DM, or no supplementation of vitamin E, the higher rate of supplementation did increase the muscle concentration of vitamin E.  However, it did not affect the indicators of oxidative stress in the muscle following a submaximal exercise test.  Perhaps a difference would have been observed with a more aggressive exercise regimen.  More recently, horses supplemented at a rate of 3000 IU per day of vitamin E compared to 80 IU/kg DM, underwent a training protocol.  The anti-oxidant capacity of all the horses increased following training, which is a natural adaptation to exercise.  There were no differences in reduced or oxidized glutathione peroxidase at rest, or total glutathione peroxidase.  However after a standard exercise test, the horses receiving 3000 IU vitamin E did have more reduced gluthathione peroxidase, suggesting a greater anti-oxidant capacity. Horses exercised to fatigue following 8 weeks of supplementation of 3000 IU of vitamin E had less muscle oxidation as measured by myofibril carbonylation( a measure of protein oxidation).

(Heavily exercised horses may need more vitamin E in their diet than maintenance horses or lightly worked horses.)
Determining if your horse has a vitamin E deficiency may not be as straight forward as taking a blood sample.  It has been shown that the concentration of vitamin E in the horse’s blood  varies irrespective of diet.  In one study, the variation within an individual horse in a 72 hr period would have shown the same horse as more than adequate in vitamin E, to marginal as well as deficient.  Therefore, it may be more important to look at your feeding regimen and the feedstuffs your horse consumes to determine whether or not they may have a deficiency.  The diet your horse is on may also affect his vitamin E needs.  Vitamin E is protective against the peroxidation of lipids in the body, especially the polyunsaturated fatty acids.  Horses which consume diets higher in PUFAs, which is certainly recommended in many cases, may increase the need for anti-oxidants in the body to prevent lipid perodixation.  Thankfully, many sources of PUFAs may be higher in vitamin E content.

If your horse is older, they may also be a candidate for vitamin E supplementation.  As horses’ age, their body systems may not function at the same level seen in their younger years.  As in people, the immune system of our aged horses may begin to fail.  When horses over 20 years of age were vaccinated for influenza, they were unable to mount the same immune response as their younger counterparts.  Therefore, older horses may be prime candidates for supplements which are known to complement the immune system.  In older horses fed vitamin E at 15 IU/kg of body weight, the bacterial killing ability of specific immune cells was increased, along with an increase in some, but not all, of the specific types of immunoglobins (or antibody).  However, in this study, the horses were previously on a marginally deficient amount of vitamin E. Therefore, it is not known whether it was the correction of the deficiency or the over supplementation that yielded positive effects.
Horses are fairly tolerant of relatively high amounts of vitamin E in the diet.  The upper range of vitamin E intake has been set at 1,000 IU/kg of DM. To think of this in more common terms, we will do a brief example using an 1100 lb horse that consumes 2% of its body weight.  Thus this horse would typically consume 22 lbs of feed per day.  We will convert this to kg to look at our total amount of vitamin E the horse should ever safely consume.  22 lbs of feed is equivalent to 10 kg of feed. Thus, the upper range of safe intake of vitamin E is 10,000 IU per day for a 500 kg horse.

However, vitamin E should not be used without caution.  In human medicine supplementation of vitamin E has not always yielded positive results, and if fact can actually enhance the disease state.  In humans undergoing heavy exercise, vitamin E supplementation actually decreased some of the positive adaptations to exercise.  In addition, heavy supplementation has been actually linked to mortality. As always, supplementation is never the answer for a properly balanced diet.   Overzealous  supplementation may actually work against your horse’s health!  But if your horse is older, more heavily worked or has added poly-unsaturated fatty acids in its diet, you might want to examine your diet for its Vitamin E content.

Next month we will finish our discussion of the fat soluble vitamins with vitamin K.

A Horse is a Horse, of Course, of Course…

Posted on by — Leave a comment

Written By Walt Friedrich

Recognize the famous opening lines from the old TV show, “Mr. Ed”? Biologically, it’s a true statement. But look again: there is one huge separator in horsedom, and all horses fall into one category or the other. They are either wild/feral or domestic, and while biology and appearances are the same, the lifestyles are completely different. We’ll refer to American ferals here, though much of their condition is mirrored in the world’s true wild horses.

We, in America, can thank the Spanish of 500 years ago for reintroducing the horse onto this continent after an absence of tens of thousands of years. Columbus brought several dozen domestic horses with him, leaving them on the island of Puerto Rico when he returned to Spain, so they might reproduce and, later, serve future Spaniards in quest of wealth on this continent. Those explorers and gold-seekers used them quite handily. Thus, over time, they found their way to northern South America and Central America, ultimately into Mexico, thriving everywhere on their journey. Of course, there were escapees into wild country, notably into what is now southwestern United States, where the fugitives did what horses do – they organized themselves into bands and continued to thrive, but without aid from humankind. These were the progenitors of the modern feral western mustang. The “training” they had received while in captivity was quickly forgotten, as they gained competence in the free but dangerous lifestyle of American ferals. Learning literally “on the run”, over time these magnificent creatures thrived as a transplanted species, developing into very large herds with distinct social orders.

Then, as fate would have it, the tables turned somewhat as our West gradually became populated. Settlers tapped this now-vast resource for animals that provided transportation as well as labor – and there we were, with domestic horses as part of our lives, but with a twist. Our society lived closely enough with both domestic and feral horses that we could easily recognize their differences in lifestyle and behavior.

Good thing, that;  by bringing horses into our families in a very real sense, we are easily able to compare them with their feral counterparts. Very convenient – but by taking him from his natural environment, we also take on the responsibility for his well-being. It’s a huge responsibility, since the Caretaker of the ferals is Mother Nature herself, who can do a much better job of it than we can. Fortunately, when we hit a snag, as we often do, we can look across the way and maybe see how Nature does it.

Many of those snags we hit sort of come with the territory. The life of a feral is rather simple, and the needs are generally rather easily met. For instance, as grazers, food for feral horses consists primarily of growing plants, but stands of growing plants are often scattered in our western wilderness, causing feral herds to move constantly in quest of suitable and sufficient sustenance. It is estimated that ferals typically move 20 or more miles every day as they seek out food. Sounds like a tough life, but that’s what it makes these horses…tough. That’s a lot of exercise, it keeps them healthy and fit, burning the energy coming from the sugars in the grasses. Pretty simple – eating a variety of growing plants, lick at mineral deposits, drink fresh water, and move, move, move. The entire species’ success is based upon that simplicity.

But now consider their brothers, the domestics. Rather than in the freedom of the open range, many live fetlock-deep in relatively lush grass in our pastures, and in addition, we provide hay and grain. So they typically have little problem getting food, and they need do practically no work to get it.

What about shelter? For the feral, it’s whatever and wherever he can find it – a stand of trees, thick brush, a rockpile to act as a windbreak. Now, that’s “roughing it”. The domestic, on the other hand, often has a stable with stalls, or at least a run-in shed

Food and shelter, the basics of life. So it would appear that the advantage goes to the domestics.

But not so fast, there’s a price to pay for those benefits. The combined results of Mother Nature’s nurturing and their own genetics supports the ferals’ ability to survive and prosper in their simple but sometimes harsh reality, and Darwin’s survival of the fittest – natural selection, actually — precept keeps the gene pool healthy. Domestics, however, often live their privileged lives within the confines of a fence. A horse has evolved to move, almost constantly, and with the fenced-in restriction, it’s up to his humans to see that he gets some work – but rarely 20 miles per day!

The less-fortunate domestic finds himself living in the confines of a stall for much if not all of the time – this poor fellow misses not only movement, but also fresh air and sunshine, and, importantly, the ability to keep something in his stomach all the time by grazing. Now, who would think that an empty stomach can lead to an ulcer? Yet that seems to be the case; a stall-bound domestic, unable to feed sometimes for hours, compared to a feral, grazing a little all the time, is much more likely to develop ulcers. It is claimed by some that gastric ulcers are very common in domestics, often going undetected or undiagnosed, to the horse’s detriment.

All horses are created, designed and built to eat a variety of growing plants, and thrive on them. Grain never was on his original menu – yet it’s standard for most domestics, largely, some believe, out of habit. When a horse pulled a plow all day, he needed more energy than forage provided, and grain – carbohydrates — filled the bill. But today’s typical domestic, whose biggest workload amounts to carrying a rider from time to time, rarely needs help from extra carbs. And when an overload rushes through his digestive system and into his cecum, he’s in danger of serious complications, like colic, laminitis, founder.

The natural diet of a feral is rather nicely balanced, thanks to the variety of plants  he ingests along with the mineral licks he visits for that extra “punch”, and he takes in water untampered by civilization, then tops it off with constant exercise. The result is a naturally healthy horse, rarely afflicted with common ailments of domestics, such as colic, ulcers, laminitis, founder, navicular disease, Cushings, Insulin Resistance, even rain scald, just to scratch the surface of a long list.

Though lacking the benefits of a free lifestyle, domestics can do almost as well as long as they are properly fed and cared for. Grazing the same variety of grass every day, eating the same type of hay, hardly qualifies as a well-balanced diet, resulting in horses “old” before their time.

What can we do about it? It’s not rocket science — feed healthy and well-balanced diets, and ensure as much exercise as we can provide. The exercise part is easy and fun for both ourselves and our horse – riding! — and get him out of his stall and into the field as much as possible. The diet part means back off on the store-bought feed, then take that first, giant step: get his hay analyzed. Armed with that list of nutrients he takes in, we can supplement what’s lacking easily. But be selective, and read the labels carefully. It’s not just what’s in it, how much of each nutrient and how they balance is equally important.

A good general supplement will be rich in Omega-3s, magnesium, zinc and copper, but contain little or no iron (the horse gets all he needs from grazing) – these minerals are often deficient in pasture grasses and hays, but they are vital for good equine health. One of the best such supplements is Omega Fields’ Omega Horseshine®.

There are many laboratories that will analyze your hay. Contact your local Ag Extension for names. One of the best is Dairy One in Ithaca, New York.

There is a great little book you can buy or borrow from your library – it’s entitled, “Beyond the Hay Days”, written by Rex Ewing. It’s an excellent, easy-to-read reference on equine nutrition. It belongs on your shelf for quick reference if you’re serious about feeding your beloved equine companion properly.