Supplementing Magnesium

You've heard it's good for cresty necks, but how much do you give?
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You've heard it's good for cresty necks, but how much do you give?

Horses tend to respond well to large amounts of supplemental magnesium. It's a good mineral to be consider as a supplement for "nervousness" and cresty-necked horses, easy keepers (aka metabolic syndrome horses) and actual insulin-resistant horses. Download this story as a PDF here.

Some magnesium use the word "calm" in the title, but they're fine for cresty necks, too.

Some magnesium use the word "calm" in the title, but they're fine for cresty necks, too.

For nervous horses, it's often found in combination with thiamine (vitamin B1), as a deficiency in thiamine can also cause a jittery horse. Of course, adding magnesium and/or thiamine to a nervous horse's diet will only show results if the horse is deficient in these minerals.

They are filling dietary gaps that caused the nervousness. Giving these products to a "jumpy" horses who has no physical need for them isn't likely to make a difference. Those horses may have a training problem and/or a mental "deficiency" of some type, best addressed by a good trainer. 

Actually, that's why you hear calming products "do" work from some folks and "don't" work from others. It's related to the horse's diet. Sure, you can experiment and give these to your nervous horse, but if you don't see a result, that could be why. 

But for overweight horses, magnesium is well worth trying. As stated, most hays are low in magnesium anyway, and you may see a physical difference, usually beginning with that cresty neck. Plus, it's a low-cost option. It can't hurt to consult your veterinarian or an equine nutritionist here, though, because they may be able to help you achieve an optimal diet.

Tricks of the Trade

Magnesium needs to be balanced with calcium. Because calcium competes with magnesium for absorption, the magnesium content should be at least half that of calcium. However, hay grown in areas of acidic or clay soils are typically low in magnesium. Compound this with low bioavailability, and your equine friend may be getting just enough to prevent a full-blown deficiency but may not have quite enough to maintain normal hormonal and nervous system functioning.

Magnesium found in forages and feedstuffs is absorbed at only 40 to 60 percent. Because of this, forms such as magnesium oxide, citrate, proteinate, carbonate, and sulfate have a higher absorption rate (70%) than magnesium consumed from natural sources. To help with regional fat deposits, supplementing magnesium is a good idea. A 2:1 ratio of Ca:Mg is appropriate and it can be as high as 1:1.

Consider this example: Your hay contains 0.32% magnesium and 0.71% calcium. Twenty pounds provides 29.1 grams of magnesium (20 lb x 454 g/lb x .0032) and 64.5 grams of calcium (20 lbs x 454 g/lb x .0071). Assume that only 50% of the magnesium from your hay is absorbed; therefore, only 14.6 grams of magnesium is provided by this hay. Supplement magnesium to bring the Ca:Mg ratio to 2:1. So in this example, you should supplement an additional 18 grams (rounded up from 17.6 g) of magnesium. (Be sure to take other sources of calcium and magnesium into consideration.)

Obviously, it’s best to test your hay before supplementing magnesium. If this is not feasible, offer a full-sized horse (1100 lbs or 500 kg) a more conservative amount, say 10 grams per day. Continue supplementing until you see the fat pads start to diminish (this can take several months); then reduce the amount of magnesium by half as a maintenance dose.

Magnesium supplements are readily available, either as the individual mineral or often combined with chromium (when the product is targeting metabolic issues). When supplementing magnesium, keep in mind that the dosing will vary depending on the form used.

In order of concentration, here are the most commonly supplemented forms of magnesium:

Magnesium oxide - 56.2% magnesium (very bitter)

Magnesium carbonate – 28.8% magnesium (well tolerated)

Magnesium aspartate – 20% (amino acid chelate; highly bioavailble)

Magnesium malate - 15% (occurs naturally in fruits, grains and nuts)

Magnesium citrate – 11% magnesium (better tasting)

Magnesium proteinate – 10 % magnesium (amino acid chelate; highly bioavailable)

Magnesium sulfate – 9% magnesium (Epsom salts – significant laxative effect)

Bottom Line

You have a lot go gain and little to use by trying supplemental magnesium to help your overweight, cresty-necked horse. You still have to practice good management, of course, sticking with a low- or no-grain diet (feed all hay, hay pellets), minimizing access to grass if necessary (put them in a dry lot, sparsely grass paddock or barn for part of the day), and being sure to institute a regular exercise program (even if it’s only taking the horse for a hand walk for 30 minutes once or twice a day).

Try 10 grams of magnesium and give it 30 to 90 days to see results. It’s not a huge shrinking, of course, but you’ll note the crest doesn’t feel as thick and stiff to your touch and you'll see "fat pads" on the horse's body shrink. Once your horse looks good, you can try feeding 5 grams per day, upping gradually back to 10, if necessary.

Powder is the least expensive way to go and the magnesium descriptions above can help you choose the right one (magnesium carbonate is popular). Choose a pellet formula for horses not receiving any grain that will allow you to mix in the powder. Our chart includes products we think are good choices to consider. Coming Soon: Managing your insulin-resistant horse.