Dietary Minerals for Horses
Published in Horses and People Magazine
Macro minerals & trace minerals for optimal health
By Mariette van den Berg, BAppSc. (Hons), MSc (Equine nutrition)
Supplements for horses are a big industry! Just visit you local horse store or flick through any horse magazine and you will find a number of ads for equine supplements. Horse owners love supplements, especially minerals and vitamin supplements.
Assessing if your horse actually needs some extras and choosing between all the variants can be a big challenge for many horse owners. We never want to under feed our beloved animals but overfeeding can be as harmful. In this article the dietary minerals and their function in the body will be discussed. In part 2 we will have a closer look at the vitamins.
Origin of minerals
When we talk about dietary minerals, we actually mean the chemical elements that living organisms require to maintain optimal health. These dietary minerals can be found in all food materials including plants and animal-derived sources.
Horses are herbivores and obtain most their minerals from plants. Plants get their minerals from soil and fungi association. Fungi play a very important role in transporting minerals and energy through the soil, storage of minerals and energy in living cells and transferring minerals to plants. The plant can only be fed when the soil biology and quality is healthy. The plant will take up the inorganic minerals and convert it in the cells to organic forms that sustain the life of the plant and all the organisms that consume the plant. When a mineral is nutritionally organic, it means that it is chelated or bound to an organic compound such as proteins, polysaccharides, amino or organic acids. Horses ingest most of the minerals in these organic forms.
Chelated or organic minerals (minerals bonded to “small proteins”, peptides or amino acids) have become increasingly popular in equine supplements and feeds. Research into chelated minerals for horses has focussed on reproduction, immunity, young growing and exercising horses. Although the results of the studies are not conclusive about the uptake action of chelated minerals, it appears that the process of chelating improves the absorption of the minerals from the digestive tract. Because of this bio-availability, chelated minerals can be fed in lower amounts. The only disadvantage is that chelated minerals are expensive. Supplement and feed companies that use organic minerals will add levels that are typically at 25-30% or lower of the total mineral in the product. The remaining of the mineral premix will consist of inorganic minerals (usually oxides, sulphates etc). The problem that we sometimes see with the inorganic minerals is that competition between minerals can occur if we don’t have the balance right in the supplements or premixes. All minerals carry an electric charge, which enables them to pass the intestinal membrane by carrier proteins and free itself into bloodstream. Many minerals will compete for absorption, and too much of one mineral can reduce the uptake of a number of other minerals or trace-minerals. Chelated minerals on the other hand appear to be less subjective to competition as it undergoes a different uptake mechanism. Thus, depending on the cost and digestibility, supplement and feed manufacturers will choose either inorganic forms or combination with organic chelates.
But how much of each mineral and in what ratios do we have to feed? The Nutrient Requirements of Horses (NRC 2007) provides us with a report that collected scientific data of published mineral trails on horses. The amounts stated in this article originate from this report.
Macro-minerals
Marco-minerals are the minerals that are required in larger amounts. These include Calcium (Ca), Phosphorus (P), Magnesium (Mg), Potassium (K), Sodium (Na), Chloride (Cl) and Sulphur (S).
| Calcium | is an important element in bones and teeth and is required for various functions within the body such as muscle contraction, blood clotting, cell membranes and the regulation of many enzymes. The most common sources of Ca supplementation are Ca carbonate, sulfate and oxide or the organic chelates. There are a number of feed products commonly fed to horses that are relatively high in Ca such as sugar cane molasses and legume forages like lucerne. Some tropical and subtropical grasses are high in oxalates which bind calcium and make it unavailable for absorption by the horse. The calcium to oxalate ratio should be greater than 0.5:1 to avoid the risk of calcium deficiency. In addition, cereal grains or by-products that are universally fed to horses are low in Ca and high in phytate phosphorus which can also further reduce the Ca availability to horses. Vitamin D is needed for intestinal absorption of calcium. A lack of vitamin D will result in poor skeletal development, even if Ca was supplied in sufficient amounts. |
| Phosphorus | is also a major constituent for bone development and growth. It is required for energy transfer reactions, synthesis of phospholipids, nucleic acids and phosphoproteins. There is close link between P and Ca and the intake of these two minerals must be adequate and in the correct ratio. High concentrations of Ca in the diet can depress P absorption, conversely when Ca intake is less than P intake (ratio less than 1:1), calcium absorption may be impaired and can cause hyperparathyroidism (Big Head). In addition, diets that contain high concentrations of oxalates can also reduce P availability. To ensure P absorption correct levels of salt have to be consumed by the horse. The most common form of P supplementation is Dicalcium phosphate also known as DCP. |
| Magnesium | is needed for bone, blood, enzymes and muscle contractions. There are a number of sources used in supplements and premixes including oxide, sulfate, carbonate, organic chelate and other types. Excess P intake should be avoided as it is known to reduce Mg absorption. Clinical signs of Mg deficiency include muscle tremors, nervousness, ataxia and collapse. |
| Potassium | is involved in a number of body functions including muscle contraction, nerve impulse conduction, heart rhythm, cell membrane potential and acid base balance. K can be found in a number of forages and oilseed meals. The most common inorganic sources for supplementation are K chloride and carbonate. |
| Sodium | is generally supplied as NaCl salt. It is important for electrolyte balance, body fluid volume and brain and nerve function. Most horse owners supply salt in the form of a lick block. However, voluntarily intake may vary per day and per horse.It is therefore advised to still supply salt in the ration. Horses with sodium deficiency can show symptoms such as licking objects, decreased skin tugor, poor appetite and decreased water intake and muscle contractions. |
| Chlorine | is bond to Na when supplied as chloride and is needed for the same function and shows the same clinical signs when deficient as Na. Excess Na intake (from sodium bicarbonate supplementation) can reduce Cl absorption. |
| Sulphur | can be found in essential amino acids methionine and cysteine, and all polypeptides, proteins and enzymes that contain these amino acids. It is also a component of the B vitamins, thiamine and biotin, insulin and chondroitin sulfate. S is present in plant proteins. S deficiency in horses has not been reported. However, excess has shown to cause colic, lethargy, yellow membranes and frothy discharges. |
Trace-minerals
Trace-minerals or micro-minerals are required in smaller amounts then the macro-minerals but they are as essential as the big ones. The group includes Copper (Cu), Cobalt (Co), Zinc (Zn), Manganese (Mn), Selenium (Se), Iodine (I) and Iron (Fe).
| Copper | is a major component of the oxygen carrying part of blood cells. It helps protect cells from being damaged by certain chemicals in the body and it keeps blood vessels and connective tissue elastic and flexible. Cu is also required for the mobilization of iron stores and melanin synthesis (skin pigment). Sources available include oxide, sulfate and organic chelates. Cu interacts with a number of other minerals, including Mo, S, Zn, Se, Fe and others. Research has shown that very high Zn intake resulted in secondary Cu deficiency in weanling foals. Cu deficiency can affect bone development causing lameness and limb deformities. To avoid Cu deficiency the ratio of Cu:Zn should be at least 1:4-5. |
| Cobalt | is an essential element in the production of vitamin B12. Vitamin B12 is necessary for the normal formation of all cells, especially red blood cells. Co can be supplied in the inorganic carbonate, chloride, sulphate form or the organic chelated form. Co deficiency appears to be rare in horses as they probably obtain adequate amounts through the consumption of normal feedstuffs. |
| Zinc | is an important constituent of hundreds of enzymes and is needed for the formation of connective tissue (ligaments and tendons), the growth and repair of tissues (skin, hair etc) throughout the body and the immune system. The most common supplement sources used are oxide, sulfate and organic chelates. Zn deficiencies in foals can cause poor appetite and reduced growth rate. |
| Manganese | is important for carbohydrate and lipid metabolism and the production of chondroitin sulphate for cartilage formation. Mn can be supplemented in the oxide, sulfate or organic-chelate form. Excess amounts of Mn can reduce P absorption. |
| Selenium | is required for proper functioning of the thyroid hormone metabolism and protects cells from certain damaging chemicals. Together with vitamin E, it also helps the immune system produce antibodies. Se can be found in organic forms in plants and seed grains. Inorganic forms include sodium selenite and selenate. Too much Se can be toxic to horses, causing mane and tail hair loss, lameness, hoof problems, blindness and death. |
| Iodine | is mostly found in the thyroid gland, where it is used to produce thyroid hormones to regulate basal metabolism. Iodine is commonly supplement in the form of iodized or trace-mineralized salts (e.g. potassium iodate). Overfeeding as well as underfeeding iodine can reduce hormone production which results in goiter (swelling in the thyroid gland). |
| Iron | is needed in many enzyme systems and is required for the transport of oxygen in red blood cells. Horses that are stabled or maintained on poor pasture have a higher chance of developing Fe deficiency. The first sign of Fe deficiency is anaemia. Excess Fe can be very toxic, especially in young horses, and can result in death. |
Other minerals
There are a number of macro and trace minerals that are not discussed in this article. These include Molybdedum (Mo), Chromium (Cr), Fluoride (F), Silicon (Si) and Boron (B). It appears that most horses obtain adequate amounts from their normal feed. Mo and Cr are two that you may see listed on feeding labels. Mo is an essential component of various enzymes and can be found in higher concentrations in the liver, kidneys, skin and bones. It is also important for cell growth. Deficiencies may result in anaemia, loss of appetite and weight and poor growth in young animals. Cr is needed for carbohydrate and lipid metabolism and is a reagent that enhances sensitization of insulin to facilitate glucose clearance. It is therefore used in feed products to reduce blood glucose levels and may be beneficial in horses with tying up. Organic forms of Cr appear to have a better bioavailability than in inorganic forms.
Still unsure if you are feeding correctly? For more information about feed evaluation and recommendations contact MB Equine Nutrition Consultancy for a consultation.
Table 1: Minimum daily mineral requirements of adult non-working horses (mature BW 500kg)*
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