Feeding horses hay, as nature intended, seems to be a developing trend in equine nutrition. Aim to feed a healthy 2% of the horse's body weight in hay.

If I had to sum up the direction that feeding horses is going, it would be back  toward the basics. Overall, I see a trend developing to feed horses as nature intended them to eat. Some of this movement is fad and exaggerated to a degree, but evidence is piling up from several different directions to support the basic observation that horses are supposed to eat grass.

Fat Horses
As an example, obesity is certainly nothing new in the horse world. However, it’s getting more attention lately because of the potential link with serious health problems, which is finally coming to the forefront. Fat ponies that will founder on grass have been around forever. But now we’re recognizing that "easy keepers"—or, frankly, overweight horses—might be prone to laminitis, as well, and we understand that this propensity is linked to insulin resistance.

In 2007, veterinarians from the Virginia-Maryland Regional College of Veterinary Medicine studied 300 horses living on pasture that were owned by their field-service clients. They found that 51% of the horses were overweight, and that 19% of the overweight horses were obese. Of that 19%, 32% had elevated blood insulin levels, an indicator of insulin resistance. Of the 32% that were overweight but not obese, the numbers reversed, with 18% having high insulin.

The recognition of insulin resistance as a nationwide problem has led to an explosion in new bagged-feed choices that are lower in sugar and starch, the two simple carbohydrates that the horse digests into glucose.

Feeding meals high in sugar and starch is known to decrease sensitivity to insulin. In short, these new feeds are moving closer to what the sugar/starch profile of a horse’s diet should look like—grass. This is an improvement, but there are some things you need to know:

• Feeds that are "low starch," "reduced starch," "safe," etc., aren’t necessarily low calorie. In many cases, the calories that were coming from high-starch grains and molasses have been replaced by fat calories.
• Because they’re not necessarily low calorie, you can’t substitute these feeds for your current feed and expect your horse to lose weight.
• Fat increases or even causes insulin resistance in other species. It’s known to cause insulin resistance in ponies; there’s some evidence to suggest caution with feeding high-fat feeds to insulin resistant full-size horses as well.
• The new reduced-simple-carbohydrate feeds are always lower in starches and sugars than the more familiar grain-based feeds, but they’re not necessarily low enough for an insulin-resistant horse, especially one dealing with laminitis, which makes him unable to exercise.

Hays vary widely in how much sugar and starch they contain, but typically they’re well below 20%. For a horse that’s actually insulin resistant, the target is no higher than 10% when he isn’t being worked.

Items such as rice bran and many grain byproducts often contain 25% or more sugar and starch. Since most of these feeds don’t provide information on the label about sugar and starch content, you’ll have to call the manufacturer to find out.

For the best available comprehensive information on feeding an insulin-resistant horse, consider joining the Yahoo Cushing’s and Insulin Resistance group (http://pets.groups.yahoo.com/group/EquineCushings/). This group is made up primarily of horse owners, but also includes veterinarians, researchers, and hoof care professionals. Membership was at 6,347 and growing steadily at press time.

The bottom line for feeding overweight or insulin-resistant horses is to keep it simple. A diet based on salt, a low sugar/starch hay, vitamin E, and minerals to supplement what’s missing in your area will get the job done.

Bagged feeds have a longstanding place in your horse’s diet when monitored closely for starch and sugar content. Excesses in these areas can cause dietary imbalances that could eventually lead to obesity or even insulin resistance.

Skinny Horses
If your horse needs to gain weight, your first instinct is probably to reach for grain. However, horses have fewer digestive-tract problems and the most efficient utilization of their diet if they can eat nearly constantly.

First, put your skinny horse on free-choice good hay or pasture. If this doesn’t work and there are no correctable causes for poor weight gain (such as dental problems, internal parasites, etc.), you may be interested in some of the new digestibility information from the National Research Council’s 2007 Nutrient Requirements for Horses. You can find this publication for purchase at amazon.com.

The estimated calorie content of diets high in fat or high in soluble fiber (a form of fiber that’s very easy for the horse to ferment) has been underestimated in older feeding tables. Rice bran, a relatively high-fat feed, was underestimated by 20%, beet pulp by 20%, and soybean hulls by a whopping 42% to 52%.

All of these grain options have calorie contents very similar to plain oats. They also have the added bonus of the fermentable fiber content compared to grains, which helps support the organisms in the intestinal tract.

Feeding Fat
Fat feeding is certainly another commonly used way to put weight on a horse, but it’s not completely without disadvantages. Feeding fat in high amounts may have negative effects on the organisms in the intestinal tract. It also has the potential to tie up magnesium and limit its absorption. As mentioned earlier, fat may not be well tolerated by horses with insulin resistance, even though high-fat feeds result in lower insulin responses. This needs more study in horses that are actually insulin resistant.

Fat feeding is said to make horses less excitable, and there’s some evidence to suggest that this is true, but the reason isn’t clear. Some think it’s because the horse put on fat feeding gets less quick energy from starch. Some horses get downright sluggish on fat feeding. High levels of fat in the diet can decrease energy production from carbohydrates in muscle. This may explain why feeding fat can help reduce the potential occurrences of more than one form of tying up.

A horse’s natural diet is very low in fat—no more than 5% to 6% in grass. When grass is cut, cured, and baled as hay, about half the fat is destroyed. Grass contains high levels of omega-3 fatty acids. Omega-3 fatty acids are "essential" in the diet, meaning the horse’s body can’t manufacture them. The other family of essential fatty acids is the omega-6 group. The ratio of omega-3 to omega-6 in grasses is around 4:1.

Omega-3 fats are used to manufacture substances that tame inflammatory and allergic reactions, while the omega-6 fats go toward inflammatory chemicals. To restore the intake of essential fatty acids for horses on hay and no fresh grass, you can feed whole flax seed, freshly ground flax or ground stabilized flax products, about four ounces per day. Flax seed is the only easily available source of vegetable/plant oil that has this high omega-3 content. As an added bonus, it’s very high in fermentable fiber and low in starch, starch being less than 5%.

Horses allowed to graze reap the maximum benefit from the high levels of omega-3 and omega-6 fatty acids found in abundance in grass. These powerful anti-oxidants also help build sound immune and anti-inflammatory systems.

Salt—whether in block form as seen here or as loose table salt added to pelleted feeds—is essential for all horses to meet electrolyte needs, both for sodium and for chloride.

Hay for Electrolytes
Horses lose tremendous amounts of electrolytes in their sweat. About 50% of the sweat electrolytes lost are in the form of chloride. Until the 2007 NRC Guidelines, chloride has largely been ignored. Thanks to work being done in Europe, we now know a lot more.

You probably know that endurance horses typically are supplemented with large amounts of electrolytes on rides. You may even do it yourself in the summer, depending on your climate. A few years ago, French researchers conducted an experiment in which they stopped supplementing their international-level endurance horses with electrolytes except for salt. They found the horses ate and drank better, and performed just as well. How could this be?

Older versions of the NRC recommendations didn’t even list the horse’s daily requirement for chloride. They assumed any horse getting enough supplemental plain salt (salt is sodium chloride) would automatically get enough chloride.

It turns out that this assumption wasn’t even close. A horse getting an ounce of salt a day would get 17 grams of chloride, but thanks to work done in Germany, we now know that an 1,100 pound horse actually needs 40 grams of chloride per day, and that doesn’t even include what exercising horses lose in sweat. Small wonder that low blood chloride is the most common electrolyte abnormality in horses working longer than two hours.

If we’ve been so far off on giving horses enough chloride, why haven’t there been even more problems? Well, it turns out that grains, seeds, hulls, and brans are very low in chloride. On the other hand, hay is a good source of chloride, having from 0.45% to 0.9% chloride, which works out to be from two to four grams per pound. Once again, hay turns out to be an ideal food.

The two other electrolytes lost in large amounts are sodium and potassium. Everything horses eat is low in sodium. This is why all horses need plain salt in their diet. On the other hand, potassium is present in hay in very high amounts. As little as five pounds a day will meet potassium requirements.

A horse that grazes or is frequently fed throughout the day can meet sweat losses from hay alone. The take-home lesson here is this: If you’re packing for a day on the trail, pack plain hay pellets and plenty of salt.

What About Protein?
Another thing that seems to always be on people’s minds is protein. Witness the following statements: "Different horses need different protein levels in their feeds." "Alfalfa hay is too high in protein." "Grass hay isn’t high enough in protein."

Actually, none of these statements is correct.

Your horse’s protein requirements aren’t a set percentage. An 1,100 pound horse in light work is now considered to need about 1.5 pounds of protein per day. If your horse was relying on his grain for his protein, you’d have to be feeding 15 pounds of a 10% protein grain to get that much.

Alfalfa is much higher in protein than grasses, but no higher than good pasture in the early parts of the grazing season. Even grasses have protein levels this high early in their growth. It won’t hurt your horse to eat extra protein; he just needs to drink more water to urinate out the byproducts of breaking down extra protein.

It’s also not true that grass hays are always "deficient" in protein. Let’s do the math. If your 1,100 pound horse needs 1.5 pounds of protein a day, and he’s eating 22 pounds of hay, how much protein would the hay have to contain to provide that much protein? The answer is 1.5 divided by 22 = 0.068, or only 6.8% protein!

The final gem in the crown of hay or grass as a protein source comes from the amino acid profile. Protein, including the protein in your horse’s muscles, is built by stringing together individual amino acids, like beads on a necklace. Each bead represents a separate amino acid.

We still don’t know much about the requirements for individual amino acids, but the 2007 NRC Guidelines has provided detailed information on the amino acid levels in hays and feeds, as well as a breakdown of the amino acid levels in horse muscle.

The guidelines suggest—and this makes sense—that since muscle contains by far the most protein of any of the horse’s tissues the amino acid levels in muscle might be a close estimate of a horse’s dietary needs. If you compare the pattern of amino acids in muscle to levels in hay and other feeds, hay is a very close fit. This makes perfect sense too. After all, the horse’s natural diet is grass. Feral horses wouldn’t fare too well if they couldn’t get what they need from the plant materials available to them naturally.

The pattern of amino acids—the building blocks of all proteins—found in hay is now known to match the levels found in a horse’s muscle tissue very closely. Fresh, clean hay again proves to be the ideal diet for a horse.

Muscle Questions for the Future

Although there’s only one preliminary study so far showing this, research published about two years ago found that feeding double the currently recommended levels of the amino acids lysine and threonine resulted in better muscling in both young and older horses when they were being exercised. Since feeding recommendations for horses are always geared to minimums—that is, the lowest you can get away with—it would be a surprise to find that in this case a little more is actually optimal. If your working horse isn’t muscling up like you think he should, try some supplemental lysine and threonine.

How Much Should I Feed?
The 2007 NRC Guidelines now have equations for determining the baseline calorie needs for three different levels: Minimum, Average, and Elevated. This is said to correspond to a range of horses from very lazy or stall bound, to average, to very energetic or nervous. In earlier versions, a common rule of thumb was to feed 1.5% to 2% of a horse’s body weight if he’s not being worked, 2% to 2.5% for up to moderate work, and so on.

What this really boils down to is that horses are individuals and need to be fed that way. If you had three horses that all weighed exactly the same on the scale—let’s say 1,200 pounds—one a Quarter Horse, one a tall, rangy Thoroughbred, and the other a young, growing draft horse, you probably wouldn’t like the results if you tried to feed them all the same.

The bare minimum a horse should get in hay is 1% of his body weight, or one pound for every 100 pounds of weight. A healthier starting point is 2%. If the horse is too heavy on this, scale back. If too light, increase it. Don’t consider feeding grain unless the horse is eating all the hay he can and still needs to gain weight.

What About Forage Balancers?
It’s no secret that hays or grasses that are perfectly balanced and contain adequate levels of all minerals are rare. After all, horses are meant to eat a variety of plants, not the same dried hay for months on end. Drying hay also destroys omega-3 fatty acids and Vitamin E.

The number of products on the market calling themselves forage balancers or diet balancers is rapidly growing. These are vitamin and mineral supplements, usually in pelleted form, that are designed to be fed at one to two pounds per day. They’re typically formulated to provide from 50% to 100% of the horse’s daily minimum requirement for important minerals.

These can work well for horses on hay-only diets, but they don’t really "balance" anything. Mineral levels in hays vary widely depending on plant type, region, weather, growing conditions, soil treatments, etc. No one product with a set formula can possibly balance them all.

If you don’t have any severe imbalances in your hay, they’ll be okay. Vitamin E levels are usually too low, though, and part of the reason for this is that Vitamin E may not hold up too well in a mixture. You’ll also need to add flax seed separately.