The role of iron in the equine diet
I know, the above is certainly not an image of iron oxide. But it is a lump of magnesium oxide before crushing to a powder, and while this blog is about the role of iron in the equine diet, there's an interesting connection to magnesium oxide, which features highly in the equine diet.
Mineral Types & A Bit About Magnesium
One of the first minerals I ever became aware of was magnesium, back in 2007 when I started researching going barefoot for my horses. Pretty much the only type of magnesium you could get back then was magnesium oxide, yet these days there are many different forms of magnesium we can feed our horses, i.e. magnesium carbonate, magnesium sulphate, magnesium-l-aspartate, to name a few.
There are also hundreds of papers published on it being vital for overall health, advising us that it's directly required daily for hundreds of chemical reactions in the body, and especially for nervous system and muscle function, energy metabolism and production, and with deficiencies manifesting in horses as nervous or wary, muscle tremors, poor work tolerance and the possibility of tying up.
Cut to today and the subject of mineral balancing has exploded onto the scene, considered an absolute essential part of the feedbowl. However, it's not just about the different minerals themselves, from your calciums to your zincs - for those of us non-chemists, the different mineral types, i.e organic, inorganic, chelated etc., can be baffling, and let’s not forget absorption rates and percentages of mineral content – more mineral minefields, and real brain-ache for those of us in the non-chemist club, of which I’m a paid-up member. When I finally went the barefoot way, each week I would make up little pots of powders and potions to feed my horses, but when forage balancing became the rage, my kitchen became a regular dustbowl with clouds of the stuff everywhere and me getting an uninvited lungful way too often.
However, I soon had it pretty much licked, and a couple of years ago we produced our own mineral forage balancer, EquiVita, along with a decade's supply of super-strength rubber gloves and a crate-load of nifty face-masks.
But - I was still fairly clueless when it came to the chemical side of it all, and all those mineral-related organic/inorganic words were still a mystery to me (completely different to a plant grown with - or without - chemicals!), so off I went to research, and the following is pretty much what I came up with. First off, I wanted to know a bit more about the differences between Inorganic & Organic minerals (mini Science Alert coming up).
- Organic compounds are those that are bonded to carbon atoms (although just to confuse matters, carbon on its own is an inorganic mineral).
- Inorganic compounds are not bonded to carbon atoms.
- An example - two hydrogen atoms and one oxygen atom combine to form a water molecule H2O, which makes water an inorganic compound. Minerals dissolved in water are also inorganic ie. sodium and chloride in sea water.
- Simples! Not . . .
Now here’s a thing - studies indicate that apparently it makes no difference to the body whether minerals are organic or inorganic when ingested - bear in mind I haven’t seen this research so can’t quote from it. But (apparently) the body knows instinctively what type of mineral is in the diet and what to do with it. There's no argument that when a mineral-deficient diet is supplemented with (balanced) inorganic minerals, there is a noticeable improvement in health. The body does not necessarily need its minerals bonded to carbon to be effective and utilisable.
So what do our horses get from their forage? Organic sources of minerals typically come from plants. A plant takes up its minerals from the soil through its roots, they then combine with water and push through the plant, and the plant then uses them in its photosynthetic and metabolic processes. Inorganic sources of minerals come from soil attached to the plant material and also from natural drinking water with dissolved rock material, so minerals available from drinking water will vary depending upon the source of water. The horse has evolved to be able to absorb minerals from both plant and water sources.
Now to manufactured minerals, aka Chelated . . .Organic and inorganic minerals can also be manufactured, and this is known as chelated. Chelated minerals are those that have been man-made to attach a mineral to an organic compound. Naturally, this process adds a cost to the product.
A bit about Magnesium, and those percentages . . .Magnesium is a naturally occurring mineral, and horses get around 60-100% of their daily magnesium needs from their forage, absorbed at a rate of between 40 - 60%.Magnesium deficiency occurs when there is strong grass growth – rapid growth grass is likely to be low in magnesium and sodium, and high in nitrogen and potassium. High potassium slows magnesium uptake while high sodium helps magnesium uptake (hence another reason why adding salt to the diet is beneficial), with calcium, phosphorus and fats in the diet also influencing the ability to utilise and store magnesium. It's that 'balance' thing again.
Magnesium Oxide (MgO) – Magnesium oxide, or magnesia, is a solid white hygroscopic mineral that occurs naturally as 'periclase', which Wiki describes as 'a colourless mineral consisting of magnesium oxide, occurring chiefly in marble and limestone', apparently usually found in marble produced by metamorphism of dolomitic limestone. Metamorphic rock makes up a large part of Planet Earth’s crust.MgO is one magnesium atom (Mg) bound to one oxygen atom (O). Studies show that magnesium oxide is absorbed at a rate of 70%, and by weight, MgO is 60.3% magnesium. This means that for a horse to absorb 15mg it would require 35mg of magnesium oxide. These levels are considered good concentration and absorption rates.
Magnesium-l-aspartate – Magnesium-l-aspartate is chelated magnesium. It is magnesium bound to an amino acid which makes it more easily absorbed - chelated magnesium achieves close to 100% absorption. But – before we get excited, the concentration of magnesium here is low at just 15.6%. This means 96mg of magnesium-l-aspartate would need to be supplemented for a horse to absorb just 15mg.Due to the expensive nature of chelated magnesium products, the inorganic form of MagOx provides much better value due to the higher levels of concentration and absorption rate. And comparing the absorption rates between naturally sourced organic magnesium from forage and the absorption of inorganic forms (magnesium oxide, carbonate, sulphate), both the inorganic and chelated forms of magnesium can achieve higher absorption to that of magnesium naturally found in our grazing.
To concludeThis is all well and good, but let’s also not forget the importance of a healthy gut to maximise the nutrient absorption. Digestion and absorption for all minerals is dependent upon a healthy functioning digestive system. Horses eating a high roughage diet and with constant gut motility will be far more efficient at absorbing valuable minerals than horses fed low roughage diets with limited gut motility.
The Calcium:Phosphorous Connection
Calcium and phosphorus are essential for sound and normal bone development – bone structure is 35% calcium and 17% phosphorus.Together they help compose bone, and they play major roles in metabolic activity. Hormones tightly regulate their levels in the body to maintain a balance between the two, as both calcium and phosphorus dance between different parts of the body as needed via bone, blood and tissue and back again.Calcium ranks as the most common of the body’s minerals, while phosphorus is the next most abundant.In addition, calcium is essential for normal muscle contraction where it is needed to activate potassium ion channels. It is a cell membrane transmitter and regulates enzymes and their actions. Nearly all the body’s calcium is in the bones (99%) and the remaining 1% circulates in the blood stream.
Phosphorus is essential for energy production in cells. Approximately 80% of phosphorus is in the bones.The calcium: phosphorus ratio and its interventions with other minerals and compoundsThe calcium:phosphorus ratio is critically important for your horse’s nutritional wellbeing, as well as the absolute amount of each mineral fed. All diets should have more calcium than phosphorus – most requirements yield ratios of 1.2:1 to 1.4:1.Every gram of phosphorus eaten by the horse must be matched by calcium before the calcium can be absorbed across the intestinal wall. Diets high in grain, bran and alfalfa will affect the ratioIf the dietary level of calcium is low the efficiency of absorption increases.If there is excess calcium in the diet, less will absorbed by the gut and more is excreted in the urine. If this isn’t confusing enough then consider the role other minerals play:
- high magnesium levels increase calcium absorption, but excess phosphorus will decrease calcium absorption.
- High zinc levels will decrease calcium and copper absorption, while high calcium levels will interfere with copper, manganese, zinc and iron absorption.
- High calcium levels limit phosphorus absorption, with high sodium and chloride levels increase phosphorus absorption by 30-60%.Regulation of calcium levels in the blood and bone
Providing our horses have a healthy, adequate amount of forage to browse on, the system seems to regulate mineral levels fairly well. Calcium levels in the body are regulated by Vitamin D and by the hormones calcitonin and parathyroid hormone. Blood levels of calcium are maintained in a very narrow range to ensure normal neuromuscular activity.The body will sacrifice optimal bone strength to maintain normal blood calcium levels. If daily calcium requirements aren’t sufficient from the diet, then parathyroid hormone is released to take calcium from the bones to circulate in the bloodstream.If the blood calcium levels get too high, calcitonin and parathyroid hormone act to decrease gut absorption and increase urinary excretion. Vitamin D is needed to help with absorption of calcium and to a lesser extent phosphorus from the gut.Signs of calcium deficiency and excessSigns include shifting lamenesses, weak bones, ostepaenia (crooked bones and enlarged joints), spontaneous fractures of bones, tying up, and poor performance. These are non specific signs that can mimic other conditions so a thorough veterinary check is essential.A horse with calcium depletion can take up to twelve months to correct the problem.Low blood calcium levels can present as Staggers, and Thumps - both are medical emergencies and need veterinary intervention.Staggers is a repeated prolonged contraction of muscles, especially of the face and limbs, caused by low blood calcium. Staggers can occur in horses with marginal blood calcium levels where they start twitching, spasming and have rigid, stiff legs.Thumps are a synchronous diaphragmatic flutter where there is very low blood calcium, potassium and chloride from excessive sweating. The phrenic nerve becomes hyperactive and irritable and the diaphragm thumps in synchrony with the heartbeat.Consequences of phosphate deficiency and excessHigh phosphorus levels will lead to chronic calcium deficiency which leads to nutritional hyper-parathyroidism (big head). Deficiency of phosphorus will lead to soft bones.Dietary sources of calcium and phosphorusMost grassy hays contain low to moderate levels of these minerals whilst cereal grains are low in calcium and high in phosphorus. Bran is also a rich source of phosphorus but very low in calcium. Alfalfa has a high level of calcium and very low phosphorus – if alfalfa represents more than 50% of the feed ration there will be excessive calcium and protein in the diet. How much calcium and phosphorus does my horse require?This depends upon our horse’s age, stage of growth, workload, and pregnancy/lactation status in a mare.
- It is generally accepted that an average 500kg adult horse on a maintenance workload requires approximately 20g calcium and 14g phosphorus per day for maintenance needs. This equates to calcium being 0.21% and phosphorus being 0.15% of the daily diet.
- However, a horse in very hard work requires 0.31% calcium and 0.23% phosphorus in the diet (a 48% increase in calcium needs and 53% increase in phosphorus needs over maintenance levels).
- Senior horses over 20 years may require more phosphorus than adult maintenance. Excess calcium intake should be avoided in older horses.
- Foals and youngstock needs are again different, i.e. foals (4mo’s) require 0.62% calcium and 0.34% phosphorus in the diet; 2yr-olds need 0.28% calcium and 0.15% phosphorus.
- A pregnant mare in the last 90 days of gestation requires a diet with 0.4% calcium and 0.3% phosphorus. A lactating mare with a foal up to three months of age requires 0.47% calcium and 0.30% phosphorus in the diet.
Copper (Cu) belongs to a group of elements known as trace elements, in that they play a major part in different areas of the body and are essential to health and bodily functions, yet are required in the body in very small amounts.However, without them, the consequences can be extremely harmful to heath. Copper is one of the most important trace elements in the horse, alongside zinc, iron, iodine, manganese and selenium.Since copper is a metal and the body cannot make it, it has to be introduced through diet.All parts of the body use copper in some way or another. Copper helps strong bones and connective tissue, and supports the action of melanin to pigment the skin and hair, the formation of elastin which lines blood vessels, blood manufacture, pigment formation, and for normal reproductive and immune system function.Horses require from 10-30 mg copper/kg. Forage copper levels vary widely from 3-20mg/kg with most grasses and hays around 9mg/kg dry matter. Unlike sheep, toxicity in horses is extremely rare as they do not accumulate copper in the liver, although secondary copper deficiency can occur when other minerals interfere with copper absorption.