Minerals for a Dressage Horse

How much is too much?

Q: I’m aware that my horse needs magnesium, potassium and calcium in his diet. However, I have noticed that these minerals are in his supplements, electrolytes, ulcer preventive, muscle-recovery product and multivitamin. Is it possible for him to consume too much? How can I figure out the total amount he’s receiving?
Name withheld by request

Peter Bollen

A: Yes, you can give too much of these and certain other minerals. Oversupplementation has become a serious problem, particularly with today’s sport horses starting training and competition at an increasingly young age. Sport horses require special attention to the necessary amounts of calcium and phosphorus, which are crucial for strong bones, tendons and muscles. Both minerals are lost during perspiration and frequent urination that results from increased water intake following effort. The metabolism is also affected: Bone tissue is more active during exercise, causing the horse’s system to use up nutrients more rapidly. Magnesium, a normal element in the bones and in many enzymes, is important for the brain and muscle tissue to function well.

Well-meaning horse owners often mistakenly think that mega-supplementing is a magic bullet. Some provide an array of ailment-specific supplements on a daily basis in addition to a wide-spectrum general supplement for overall health without considering the combined effect. Doing so is often financially wasteful, environmentally harmful and of little to no benefit to the horse. At times it is even counterproductive and can create serious long-term health problems. Unfortunately, signs of mineral excess (or deficiency for that matter) are not always immediately noticeable. In most cases, the problem may not be discovered before irreparable damage has been done. The result may be a premature end to an equine athlete’s career.

The good news is that it is not difficult to determine the proper amount and balance of minerals for your horse once you understand the basic science. A key factor is that minerals can influence each other. Feeding one mineral in excess can cause the deficiency of another by decreasing its absorption, in effect robbing the horse of the nutritional balance you’re trying to achieve. At the same time, the horse’s body has to work harder to excrete an excess, which taxes the system. This means you can’t look at oversupplementing alone; it goes hand-in-hand with undersupplementing.

If you feed your horse a combination of supplements, gather them together and make a list of the amount of each mineral contained in each product. Add them up to compute the total. At the same time, look at your horse’s feed-bag label to see how much of these minerals already are contained in his daily ration. Many performance horses are given a cereal-rich diet, such as oats, which contain too little calcium. 

Total mineral contribution and availability from all parts of the ration (forages and roughages, concentrates and all supplements) should be considered when evaluating mineral intake. If the horse eats mostly roughage, with little or no grain, phosphorus is more likely to be lacking than calcium. Conversely, if more grain than roughage is fed, look for a calcium deficit.

How can you determine how much of these minerals your horse needs? As a general rule, full-grown horses require about 30 grams of calcium and 20 grams of potassium a day. Growing foals and sport horses have higher needs: 75 grams of calcium and 45 grams of potassium for foals, and 40 grams of calcium and 30 grams of potassium for sport horses.

Calcium, which constitutes 35 percent of bone, is required for its formation as well as muscle contraction, blood coagulation and the regulation of cell functions, enzymes and hormones. If there is too little calcium in the blood, the horse’s system releases it from the bones, weakening them and making them porous. In contrast, too-high levels of calcium negatively affect the metabolism of phosphorus, manganese and zinc.

Phosphorus, which makes up 14 to 17 percent of bone, is needed for its formation and has a great number of other functions in the body. When a horse is deficient in phosphorus, his bones grow more porous, his food intake decreases, his performance declines and he may start cribbing. Excessive amounts of phosphorus contribute to the formation of insoluble compounds with calcium, magnesium, zinc and some trace elements in the small intestine. These compounds are dissociated in the large intestine, whereby the phosphorus is resorbed but the other elements are not. 

Clearly an excess of phosphorus has a larger impact on the resorption of calcium than an excess of calcium on the resorption of phosphorus. Therefore, it is important to ensure the right calcium–phosphorus proportion in a horse’s ration. The most desirable ratio lies between 1.4 to 1 and 2 to 1. It must never exceed 4 to 1 or be less than 1 to 1. The optimum ratio of calcium to magnesium is 1.5 to 6. For potassium to sodium, it is 2.25 to 5. This is calculated over the complete ration so that forage, grains and supplements are all considered.

Horses obtain most of their mineral needs from grass, roughage and grains. The percentage of minerals acquired from these sources can vary with the environment and soil quality. To avoid feeding errors, it is a good idea to have the main minerals and trace elements analyzed with every new harvest or delivery of new roughage. You can send a sample of your hay to an agriculture laboratory and have it tested for protein, fiber, sugar, minerals and trace elements.

Peter Bollen is the founder and head nutritionist of Cavalor, a global brand specializing in the nutritional needs of high-performance horses. During the 2010 World Equestrian Games he was head nutritionist for the Saudi and Spanish teams (






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