Common Nutrient Deficiencies in Horses
Nothing gets conscientious horse owners more in a tizzy than thinking something might be off in their horse’s diet. I don’t want to be the one to add to this worry, but it is entirely possible that your horse could be deficient in a particular nutrient without you realizing it.
Sometimes, it’s what we’re feeding (or not feeding) that throws things out of whack, but at other times, it can be more of an absorption issue (as I’ve learned with my gelding, Hershey). Older horses, especially, can have trouble absorbing and utilizing all the nutrients they consume, but so can younger horses with high parasite loads, inflammatory bowel disease, or sand accumulation in the bowel.
But horses most likely to suffer from nutrient deficiencies that don’t necessarily involve absorption problems are high-level performance horses, pregnant or lactating mares, growing horses under the age of two, or horses fed a hay-only diet. And even if your horse is on pasture, some soils and plant-types may be deficient in certain minerals (selenium, for example).
Here are some of the more common nutrients lacking in horses’ diets, as well as symptoms which go along with each deficiency:
Calcium: If horses are fed high-grain diets (which are high in phosphorus), this can throw off the calcium/ phosphorus balance and create a deficiency issue. (The ratio should be roughly 1-2: 1; calcium to phosphorus.) Symptoms of calcium deficiency inlcude: abnormal bone development in young horses, osteoporosis in older horses, hyperparathyroidism (“big head disease”), loose teeth, and weight loss. A calcium imbalance can easily be corrected by adding some legume hay into the horse’s diet and/or cutting back on grain.
Magnesium: Magnesium absorption is also dependent on calcium intake and the ratio should be roughly 1.5-2:1 (calcium: magnesium). A deficiency in magnesium has been linked with insulin resistance and equine metabolic syndrome and magnesium supplementation has been shown to help reduce regional fat deposits such as cresty neck. Other symptoms of a magnesium deficiency may include muscle cramping or tremors.
Sodium and Chloride: All horses need sodium chloride (salt) supplemented in their diet since the amounts in grass and hay are not enough. This can be provided through a salt lick, loose salt, or both (salt licks may make it difficult for some horses to obtain enough). Sodium chloride deficiencies are more likely in hot, humid climates (especially for hard-working horses). A deficiency may result in lack of muscle coordination, decreased sweating, lack of appetite, loss of performance, dehydration, or general weakness.
Zinc: This trace mineral is present in grass and hay, but may very well be deficient in some soils. Zinc absorption is closely tied with iron and copper, so imbalances are often more likely than straight up deficiencies. But a lack of zinc may present as a dull hair coat, poor hoof quality, reduced immune function, and increased likelihood of developmental orthopedic disease in foals. It can also cause low insulin levels and reduced glucose tolerance, which can lead to insulin resistance.
Copper: Copper is similar to zinc in that it’s found in forage, but can easily be deficient in certain areas or the balance can be thrown off by other minerals (usually iron). Deficiency/ imbalance often results in a faded coat color and has also been linked with developmental orthopedic disease in young horses.
Selenium: Selenium deficiency can be an issue in certain soils (see this map) in the U.S. This mineral has a narrow window of safety, so it’s not one which should be over-supplemented in any instance. The function of selenium is closely tied with Vitamin E and supplementing one can often help with the other. A minor deficiency in selenium may result in poor coat quality, work intolerance, reduced immune function. More serious deficiencies can result in cardiovascular problems, muscle disorders like ‘tying up’, and impaired reproductive function.
Vitamin E: Vitamin E is plentiful in green grass, but horses on hay-only diets may become deficient in this vitamin over time (although alfalfa hay is a good source of vitamin E). Vitamin E deficiency symptoms are similar to those of selenium (and you will often see supplements packaging both together). Symptoms of a deficiency may include reduced immunity (recurrent coughs and colds) and muscle stiffness. Older horses who’ve had a long-time deficiency in Vitamin E may have muscle wastage and loss of muscle tone as well. There are also two diseases associated with Vitamin E deficiency: equine motor neuron disease and equine degenerative myoencephalopathy (which both affect the spinal cord).
Vitamin A: Also plentiful in green grass, vitamin A is stored in the liver and utilized as needed by the horse’s body. Horses on all-hay diets could become deficient in this vitamin over time as well. Symptoms of a Vitamin A deficiency include night blindness, tearing of the eyes, dull coat, reproductive problems, and poor immune function.
Vitamin C: Vitamin C is actually produced by the body naturally, but horses under long-term stress (such as foals being weaned or horses recuperating from surgery or serious illness) can suffer from a deficiency in this vitamin. Older horses may also have trouble manufacturing vitamin C. Dr. Juliet Getty says, “Decreased liver function is the main reason, but it can also be due to a decline in hindgut microflora and an increased propensity for pituitary dysfunction.” Symptoms of a Vitamin C deficiency include lowered immune function, poor hair coat, and delayed wound healing,
Protein: This isn’t likely to be a problem unless horses don’t have access to quality pasture or hay, but some horses (especially older ones) may have trouble synthesizing proteins even in higher quality feed and forage–therefore I figured it was worth including. A quick explanation about protein: It’s made up of one or more chains of amino acids: either non-essential amino acids or essential amino acids. Non-essential amino acids can be produced by the horse’s body, but essential amino acids must be consumed in the diet (thus, the term essential!) If there aren’t enough essential amino acids in the diet long-term, then a protein deficiency can occur.
It’s not only important for your horse to consume enough protein, but it needs to be good-quality protein (those with more essential amino acids), and it also needs to be absorbed by the gut. Different protein sources have different absorption rates, so mixing your protein sources is always a good idea. For example, good-quality hay, alfalfa cubes, and split peas would all be good sources of protein.
Signs of a protein deficiency can include: decreased growth and development in young horses, slow hoof growth, low energy, loss of topline, muscle deterioration, poor hair coat with reduced shedding, and even eating manure.
If your horse is displaying one or more symptoms of a nutrient deficiency, I advise speaking to your vet about testing (some deficiencies can be determined through blood tests), testing your hay and/or pasture, or consulting an equine nutritionist. Personally, I try make sure my bases are covered by feeding a good trace mineral supplement and including a varied, forage-based diet (with whole foods added in). But even then, deficiencies are still possible, so it’s wise to pay attention to what our horses are telling us!
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