Insulin Resistance in Horses

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Eight years ago we ran a field trial on magnesium supplementation of laminitic, cresty horses and ponies. This was to find out whether the folk remedy of magnesium for laminitis really worked.

We weren’t very far into the trial when it became obvious that there were indeed benefits. Foot comfort was improving and crests going down. Reviewing the laminitis research turned up some references to laminitic ponies being insulin-resistant.

Some 12 years before we ran our trial, Dr. Gerald Reaven had given a now historical talk on what he was calling Syndrome X, a constellation of medical problems in people that included insulin resistance, obesity and a predisposition to vascular problems. One of the things found with human IR was a high incidence of magnesium deficiency. Magnesium deficiency has also been recognized to be a risk factor for developing insulin resistance. Could this be the connection' We thought so.

In 2002, Dr. Phillip Johnson published an article suggesting obesity and laminitis was an equine equivalent of human metabolic syndrome (the name that evolved for Syndrome X). This idea was widely criticized initially, but now even the most vehement critics have reversed their opinion and significant strides have been made in studying insulin resistance in horses. Unfortunately, looking at magnesium status still has not been done, but clinically many horses and ponies have had favorable responses to magnesium.

How To Use Magnesium

Even more important than how and when to supplement magnesium is to remember there are no magic bullets in the control of equine insulin resistance and laminitis. It’s imperative that the sugar and starch content of the diet be low, including sugar and starch from hay or pasture. Every horse will vary in their tolerance for sugar and starch, but once a horse is in trouble it is almost always necessary to keep combined sugar and starch content in the diet at 10% or less.

Magnesium does not work like a drug. It will only help if the horse is magnesium-deficient. This is best tested by a blood level of ionized magnesium. However, this test is most accurate when done on a fresh blood sample and therefore not practical in most circumstances.

An alternative is to look at the calcium:magnesium ratio of the diet. The early work on magnesium absorption suggested a Ca:Mg ratio of 2:1 was ideal for magnesium absorption. Hay should be most, if not all, of the IR horse’s diet, and few hays contain this much magnesium. A hay analysis is the most accurate way to determine the levels in your horse’s diet. If this isn’t possible, if you know the area where your horse’s hay was grown you can call the state university agriculture department or the local agricultural extension agent for information on average analysis figures for your type of hay.

Once armed with the analysis figures, it is relatively easy to calculate how much your horse should get. Calcium and magnesium are reported as a percentage. Unless you are feeding alfalfa or clover, the percentage will be less than 1%. For effortless math, calculate using 22 lbs. of hay, which is 10 kg (1 kg = 2.2 lb.). To convert your percentage to grams of calcium and magnesium, simply multiply by 100. If feeding more or less than 22 pounds, simply adjust accordingly.

Supplementing blindly is not wise. Feed too little and you won’t get results. Feed too much and there’s potential for diarrhea, damage to the intestinal lining, stone formation in the urinary tract, muscular weakness and change in bone structure.

Bottom Line

There are many ”metabolic” supplements out there. To assess the effect of magnesium, we suggest you keep it simple. Figure out how much you need to feed then use a supplement that doesn’t have a host of other ingredients. Bulk magnesium oxide is by far the most economical and horses absorb magnesium from magnesium oxide well.

If you want a smaller amount, Mag Ox 56 from Horse Tech is a good buy, and Uckele offers a slightly purer grade for a slightly higher price. For picky eaters, go with Quiessence pellets from Fox Den Equine.