Fun With Feed Math! Part 1: Demystifying The Label

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Written By Dr. Kris Hiney

In our previous series we discussed the energy needs of horses, how they are calculated, how they differ between classes or types of horses, and how your feeding strategies should reflect the energy needs of the horse. For this series, we are going to switch gears a little, and focus on understanding commercial feed tags. In today’s equine feed market, there are an overwhelming number of feeds and types of feeds available to select for your horse. It certainly can be bit confusing at times. Our goal is to clear up some of the confusion and allow you to make the best choices based on your horse’s needs.

Types of feeds available.Typically, concentrates (what most horse owners refer to as grain or feed) are added to the equine diet to supply additional energy that cannot be met by hay consumption, or to supply additional protein. We will consider anything not in the classification of forage or roughage to fall into the “horse feed” category. When shopping for horse feed, you should know there are different classifications of feeds available: textured feeds, processed feeds, complete feeds, and supplements.
Textured feeds.

Textured feeds are those we typically think of as sweet feeds. They contain whole grains such as corn, oats, soybeans etc. that have been processed so that the horse can digest them more easily. Typically the grains are cracked, crushed, crimped or rolled which breaks up the outer layer of the kernel to allow the horse’s digestive enzymes easier access to the internal contents of the seed. The term “sweet feed” originates with the practice of adding molasses to the feed to enhance the flavor of the feed, suppress the dustiness of the feed, and to bind together additional ingredients. As most feeds are typically fortified with vitamins and minerals vital to the horse, it is important than these ingredients do not settle out of the feed and remain uneaten. The molasses essentially helps to prevent that from happening. Plus, most horses just plain love molasses!

Processed feeds.The second types of feed commonly encountered by the horse owner are the processed feeds. Rather than being able to indentify individual grains, these feeds are either pelleted or extruded. Pelleting essentially eliminates the concern of the fine particles (such as the vitamins and minerals) from being sorted out and thus ensures that the horse is receiving all nutrients intended by the feed manufacturer. Extruded feeds are produced under pressure and heat to create a lighter, less dense product which would more closely resemble dog food. As extruded feeds take longer for your horse to chew, there are some advantages to feeding these if your horse likes to rapidly ingest its feed. Further, prolonging chew time has some real advantages for your horse’s health (which we will discuss in the coming months). While both pelleted and extruded feeds have some advantages for feeding, realize the feed company has more processing involved, thus these products will cost more.
Complete feeds.Complete feeds are those that are intended to potentially serve as the horse’s only source of feed, and may serve to replace the forage component of the feed. These feeds have a fiber source added to the more traditional cereal grains, such as chopped hay, beet pulp or other fiber sources. While they serve the same purpose of maintaining the gut health of the horse as feeding hay, your horse may not consider it the same! The amount of time the horse spends eating will be less if only these feeds are fed, with no long stem forage. Ideally for the normal healthy horse, we recommend feeding 2% of their body weight in hay per day. (More on that again soon). So who are they appropriate for? For one, the senior horses who have poor teeth. It is vital that these horses are still consuming roughage, albeit in a different form than from their younger years. Older horses may not be able to properly chew hay, but they still have the desire to forage. Allowing them a source of hay to pick through is a great way to keep the old guys happy. Complete feeds are also quite handy if your forage supply is questionable, either from lack of supply or quality. As hay making is quite dependent on the weather, there certainly may be times where it becomes necessary to feed complete feeds to horses. They may also make a handy way to travel with your horse, as they are less bulky to handle and transport than hay bales.

Omega Horseshine Bag

The final category of horse feeds available fall into the category of supplements. These feeds are designed to supply protein, specific amino acids, essential fatty acids, vitamins or minerals to the horse which may be missing from its diet. While a properly fortified textured, pelleted/extruded, or complete feed may eliminate the need for supplements, many people seek supplements to optimize the diet of their horse. Omega Horsehine® and Omega Grande® would both be examples of supplements. They are fed in amounts less than that of traditional horse feed, and are formulated to supply key essential fatty acids, vitamins and minerals. Often times horses can meet their energy needs solely from forage alone, and many supplements are designed to meet the shortfall in specific nutrients that the forage may lack. Thus some specific supplements may eliminate the need to increase the grain component of the diet and provide calories the horse doesn’t need.


The feed or supplement you select must always be based first from the type of forage or roughage your horse is consuming! This is the bulk of what your horse consumes and feeds should be selected that complement your hay. For example, if you are feeding your horse high quality alfalfa hay which is high in protein, you do not need a high protein concentrate! Always consider your hay selection first!

What does a feed tag have to tell you?First, we need to discuss what information you will always find on a feed tag. On every feed label, both the product name and brand name must be included, so that the feed is identifiable. It will also include what the product is intended for, such as the type of horse including activity level, age, and reproductive state. This will provide you with an immediate guide to determine if the feed is appropriate for your horse. If you have a young, growing horse, you should look for a feed designed to meet the increased nutrient demands for growth.
Guaranteed Analysis.

Omega Nibblers Guaranteed Analysis

The second key piece of information on a feed tag is the guaranteed analysis. The following must always be included by the feed company on every product it sells: the minimum amount of crude protein, the minimum amount of crude fat, the maximum amount of crude fiber, both the minimum and maximum amount of calcium and the minimum amount of phosphorous. All of these will be listed in a percentage basis. Other nutrients will be listed in parts per million or ppm. For equine feeds, copper, zinc and selenium will all be included on the feed tag in these units. Finally, the amount of Vitamin A will be listed in International Units/lb or IU/lb (if needed). Many times the feed companies will include much more information, especially if the feed is designed for specific types of horses.


Let’s look at Omega Horseshine’s feed tag information- as it appears on the new 20 lb bag. The values highlighted in red are those that Omega Fields is required by the Association of American Feed Control Officials (AAFCO) to provide on their label. Those in black are not required, but may be of special interest to those selecting Omega Horseshine®.

Ingredient list.Third, after the guaranteed analysis, the feed company must then include a list of ingredients used to make the feed. The ingredients will be listed in the order of the ingredient included at the largest quantity to the ingredient included at the smallest level. Manufacturers may list specific feeds (such as corn or oats) or may use the term grain products. Grain products indicate some sort of processing method has occurred such as flaking, grinding etc. You may also see ingredients listed such as plant protein products. These are collective terms for an ingredient class. For example, cottonseed meal, linseed meal, soybean meal and yeast could all be included under the term plant protein product. The company is then able to change ingredients, usually dependent on market prices and availability, without changing the feed label. This allows the company some flexibility in the manufacturing process as to which ingredients may be selected, provided it does not change the guaranteed analysis of nutrient content! Other examples of collective feed terms are animal protein products (fish meal, meat meal, bone meal, skimmed milk, dried whey etc.), grain products (barley, corn, oats, wheat, etc.), processed grain products (brewers dried grains, wheat millings, distillers dried grains etc.) or roughage products (barley hulls, beet pulp, rice hulls etc.)In looking at our feed tag for Omega Horseshine® we can see that the three main ingredients are the flaxseed, yeast and ground oats. After these three products, the next ingredients listed are the minerals followed by vitamins, which is reflective of the amount of these items required in the equine diet.

Omega Horseshine label
Other information.Finally, the feed company will usually provide other information on their feed tag, such as feeding guidelines. This may include how much of the feed to provide, recommendations on the amount of forage to be fed or other such information. Providing the feed in the amount recommended by the feed company allows the feed to function as the manufactures designed it. For example, if one fed Omega Horseshine at only 1/4 cup per day, the horse would not be receiving the amount of Omega 3, minerals, and vitamins the feed was designed to provide in a daily ration. Conversely, over-feeding a feed can also be detrimental, as you may then be providing excess nutrients to your horse.The next article in this series will look at using feed tags according to horse’s actual nutrient requirements. This will involve a little bit of math, so get your calculators ready!

Feeding Forage, Part 2: Selecting Forage

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Written By Dr. Kris Hiney

Last month we discussed how much hay you should actually tuck away before winter. You don’t want to run out before that first cutting rolls around in June! But what about the quality of that hay? This month we will talk about what to look for in a quality hay; what things you don’t have to be so strict about in terms of quality, and what makes the most economical sense.

CuttingsMany people prefer to use only one certain cutting of hay, but that largely is irrelevant provided the hay is overall of good quality. Many choose to avoid first cutting hay, but it is certainly acceptable to feed horses. One of the difficulties of first crop hay may be a larger weed content, as these plants may grow more readily at the beginning of the growing season. However, if there are little to no weeds in the hay field, this may make little difference. It is true that first crop hay may be more difficult to put up due to weather conditions. Typically it rains more at the beginning of the growing season, so there is more chance that the hay will be rained on. Certainly rain can lower the nutrition value of the hay from 40-50%. However, careful inspection of the hay will allow you to determine if your hay has been rained upon. Hay that is grown in the hottest part of the months may result in more stems and less leaves as the plant grows rapidly. This can also lower the nutritional value of the hay. Later cuttings when it is cooler may have more leaves, less weeds, and perhaps less chance of being rained upon (depending on the whims of the weather). However, your best guide is to simply inspect the hay for quality, rather than automatically simply paying more for later cuttings of hay.

One of the first criteria in selecting hay is to determine how old the plant actually was when it was harvested. The older the plant is (whether it is a legume or a grass) the more fiber content is present. Translation – the less digestible it actually will be by your horse, and the lower the energy value of the hay, and the more hay you will “waste”. Now bear in mind this may not necessarily be a bad thing, especially if you have mature horses who are easy keepers. Previously we had stated that your horses ideally eat 2% of their body weight in hay per day. But if you are feeding at that level and your horse is fat, one viable option in lowering their calorie intake is to lower the energy density of their hay by choosing more mature hays. If you want to get the most bang for your buck, you would want to select younger hays. For grass hays, you want to examine the plants for the presence of seed heads. This definitely indicates a mature plant and one that will have more fiber and less relative feed value. Seed heads that are just beginning to show through the sheath are acceptable, but if the entire seed head is visible, the plant is very mature. Also look for a color change in grass hays. As the plant matures, they change from a bright green appearance to a more dusky grey. For legumes, look for flowers. For example, alfalfa develops purple flowers with an advanced vegetative state. While that field of pretty purple might be nice to drive by and look at, it means less nutrition for your horse!


The leaves of the plant contain the most nutritional value for the horse, so look for hays with greater leaf content. In grass hays, the maturity of the plant will definitely influence leaf content, as you will get more proportional stem as the plant matures. The same is true for legumes, which will get proportionally more stemmy with advancing maturity. The handling of the hay will also influence the overall leafiness. If fields have to be raked excessively (usually to aid with drying after rain), more leaf loss will occur. If the hay was allowed to dry excessively (below 12% prior to baling and storing) leaf shatter may occur resulting in a significant loss of nutrient content. Legumes are much more prone to leaf loss as the leaves are held much less firmly to the plant than in grass hays. Even handling of the hay post storing, such as transport, feeding etc. can result in great leaf loss in legume hays.

TextureWhen examining hays, it is important to actually get your hands on the hay. Horses prefer to eat hay that is softer and more pliable. This does directly relate to nutritive value, as tougher, stemmier hay will be higher in fiber content. A good test is to grasp several pieces of hay together and twist them. If the stems break and shatter, the less acceptable they will be by the horse. This can also indicate the hay was dried too much before baling.
ColorIdeally good hay has a bright green color. This not only reflects when the hay was harvested (especially for grass hays) but also how long the hay has been stored, if it was stored properly or if it was rained upon. Hay that has been exposed to sunlight will be faded or bleached to a yellowish appearance. Many vitamins are light sensitive, so expose to sun will decrease the nutritive content of the hay. However, don’t judge a bale too harshly by its cover. Open the bale up, if it is still green inside, it will still be a quality hay for the horse. Hay that has a grayish cast or is darker than normal may be moldy or may have been rained on. Rain will make hay have a more discolored appearance and again indicates a lower quality hay.
Free from…

Here is where you really need to pay attention to your hay. Inspect the hay for the presence of unwanted items. Weeds can not only lower the acceptability of the hay and the nutritional content, but can be seriously detrimental to your horse. Many weeds are toxic to horses or can cause physical damage through ingesting sharp barbs or nettles. It is generally not worth the risk to feed weedy hay, unless you are an expert at species identification! Also look for debris or trash. Normal hay fields don’t contain twine, pop cans, beer bottles etc. This may mean your hay actually came from a ditch or roadway. All of these can cause damage to your horse. While the occasional snake or mouse might be no problem (hey it happens), be especially vigilant for bugs, especially in alfalfa hay. Blister beetles are highly toxic to horses and ingestion of just a few can cause death. Last but not least, look for mold. You may find dark discolored areas, or patches of white fuzzy mold. Moldy hay should never be fed to horses. One easy test is to just smell your hay. It should have a pleasant, fragrant smell. A musty smell indicates mold. Break the hay open and slap it. If fine dust rises into the air, avoid it as well. Commonly hay that has been baled to wet (over 20% moisture) will mold in the barn. If you happen to have the fun job of individually unloading small square bales of hay, toss aside any that feel excessively heavy to you. They are probably wet, and you don’t want to store those in your barn.

Remember, any type of grass or legume hay can be good hay for your horse (assuming they are species horses eat), provided it is good quality. Don’t pay a premium value for your hay unless you have a chance to inspect it yourself. Don’t be afraid to turn away substandard hay. It is in the best interest of your horse.

Feeding Forage, Part 1: Figuring Your Forage Needs

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Written By Dr. Kris Hiney

As this is the time of the year that hay fields are being cut and the days are already getting shorter, it is time to be filling your barns or sheds with hay for the upcoming year. This month we will learn how to estimate your hay needs so that you don’t find yourself short come April or May.

To begin, we will review some of the information covered previously. The best method to estimate hay needs is based on your horse’s body weight. If you haven’t weighed your horse yet, head out to the barn with your weight tape or your string! (See Equine Energy Requirements) Using our forage feeding rules (See Rules to Feed By), we know that at a minimum your horse needs to consume 1% of its body weight in forage per day. Now that figure is actually on what we call a dry matter basis. Most hay will run on average 85% dry matter. What that means is 15% of the hay is actually water. So let’s walk through our first calculations. Let’s assume for simplicity sake that your horse is 1000 lbs. Therefore he needs to consume a minimum of 10 lbs of feed per day on a dry matter basis. Well, what is that if I actually weight it out? Divide the amount of hay by the % dry matter (10 lbs/0.85=11.8 lbs). To finish out, at a minimum your horse will consume 11.8 lbs x 365 days/year or 4,294 lbs of hay. That means you need to figure that for your one horse you should purchase about 2 tons of hay.

Of course, that is assuming you are feeding forage at the minimum requirement. However, as we have discussed previously, feeding forage at a minimum may not be the best for the gut health of your horse and certainly for his mental health as well. In addition, horses that do not receive adequate forage to satisfy their need to chew develop very bad habits such as wood chewing, tail chewing and even cribbing. A better idea, at least where your horse is concerned, is to feed at 2% of your horses body weight per day. So with our same 1000 lbs horse, our equation is now 1000 *.02 = 20 lbs of hay/.85 (for dry matter adjustment) * 365 days. That works out to be 8,588 lbs or 4.3 tons of hay. Now that sounds a little more reasonable.

But what if your horses are outside and you are feeding them free choice hay? Horses can consume quite a bit more hay if offered, especially if their energy needs go up due to work, lactation, or cold weather, or if the hay is especially palatable. Horses can easily consume 3% of their body weight per day. That works out to a need for 12,882 lbs or 6.4 tons for your 1000 lb horse if you allow your horse full access to feed. Would there be a reason to do so? Absolutely. Many times the easiest and most economical ways to feed horses is to feed them round bales. Because there is less labor involved, round bales are often the cheapest way to buy hay. They are especially practical if you are feeding large groups of horses housed outdoors. However, unless you lock your horses away from the round bale feeder, they may certainly consume the upper limits of forage intake. For that reason, many horses can get quite fat if fed on good quality round bales.

Another consideration when purchasing hay is potential wastage. Horses will eat more than necessary if offered and become fat. They are also quite good at pulling hay from feeders and trampling it into the ground. With round bales, you can assume that 30% of your bale will be wasted via horses and exposure to the elements. Be sure to include this wastage when calculating your hay needs. You should also have a proper storage site that protects hay from sunlight and rain. Hay should not be set directly on the ground, as this can result in molding of the bottom layer. Many people try to cover hay stores with plastic or tarps to prevent wastage from rain. However, frequently the opposite is experienced. Plastic is easily punctured and allows water in, but the covering may prevent water from evaporating and only serve to further the wastage you were trying to avoid. Look at your feeding systems as well. Solid sided and bottomed feeders prevent most wastage, but horses should not be overfed, as water in feeders due to rain will result in more wastage of the hay remaining in the feeders. Never feed horses hay on the ground, as a very large percentage will be lost due to trampling, soiling on the hay etc. Further, this will result in a greater chance of parasitism through fecal contamination of hay.

How much does hay weigh?

As you can see, all of our estimates for hay needs have been based on weight. Ideally, this is how you will negotiate the price for hay as well. You should try to buy your hay on a tonnage basis, rather than by bale. For example, small square bales of a similar size can vary from as light as 35 lbs (loosely packed) or as high as 100 lbs! If your hay supplier wants a per bale price, make sure you weigh several bales (7-10) to get an accurate estimate of what you are truly paying for the hay. If you don’t have a scale for the hay, just bring a bathroom scale, hop on, and then weigh yourself holding the hay bales. Just subtract your own weight (you don’t have to have anybody look!) from the total, and repeat several more times. If you are buying hay in large square bales, round bales or by the truckload, the producer has typically already weighed the hay on a farm scale.

Buy by the BulkIdeally contract with your hay producer for enough hay to meet your needs (which we have just figured out) during the growing season. If you are forced to buy hay in the winter, expect the price to go up. Also, the larger quantities you can buy, the cheaper the cost. Perhaps going together with another horse owner to purchase loads of hay could result in greater savings. A building suitable for storing large amounts of hay may save you money in the long run over years of hay purchases.Next month. What kind of hay should you buy? What should you be looking for? What is good quality hay?

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Omega Fields® provides premium, stabilized ground flax products for equine, canine, poultry, and human nutrition. Online-based consumer distribution includes and Omega Fields’ mission is to offer the finest quality, most nutritious products at a fair price and provide outstanding customer service. We want our customers to have exceptional experience with our products, our staff, our websites, and our retailers.


Minerals for Horses: Calcium: The Building Block

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Written by Dr. Kris Hiney

This month we will return to discussions of nutrient requirement for horses. Remember we discussed energy needs for horses in the earlier articles: Equine Energy Requirements, Energy for Work, and Broodmares and Babies. Now we will look more closely at other nutrient requirements, beginning with mineral requirements. Minerals are involved in a variety of functions in the body, including enzymes, structural components, energy transfer and acid base balance. Minerals are also incorporated into vitamins, amino acids, and hormones. Thus proper mineral nutrition is vital to have a healthy horse. The minerals that are needed in the largest quantities by horses are referred to as the macro-minerals. These include calcium (Ca), phosphorous (P), magnesium (Mg), potassium (K), sodium (Na) and chloride (Cl). These minerals are needed in the diet in concentrations of g/kg or percentages, versus ppm or mg/kg of micro-minerals. Today we start with those most commonly talked about in equine nutrition, Ca and P.

A note of cautionIt is important to remember that when creating diets for horses, we consider not only how much mineral is in the diet, but also the ratio of particular minerals in relationship to others. Minerals have very complex interactions with each other, and excesses or deficiencies of minerals can greatly affect the absorption, metabolism and excretion of others. Therefore horse owners who “tinker” too much with their horse’s diet through overzealous supplementation may be doing more harm than good for their horse.

Previously in Broodmares and Babies we had mentioned that the ratio of Ca and P is always important when looking at horse rations. If you recall, we would like to see a ratio of 2:1 Ca:P, with a range of 1:1 to 6:1 being acceptable. What you should avoid is a total diet which is less than 1:1 or in other words, offers more P than Ca. This is due to the fact that phosphorous competes with Ca for absorption in the gut. Remember to calculate the entire diet however! And while the proper ratio is important, it is possible to have the correct ratio, but still be deficient in these minerals if they are in insufficient quantities in the feed. Now let’s talk in more detail about these very important minerals.


How important is calcium?
Commonly most people think of calcium’s role as that of bone development and integrity. Certainly the skeleton does account for 99% of the calcium in the horses’ body. However, Ca is absolutely essential for neuromuscular function, blood clotting, cell signaling, and an array of enzymes. Because of its importance, calcium concentrations are very tightly regulated in the blood. When Ca in the diet is inadequate, the bone serves as a major reservoir. Thus the body will sacrifice calcium within the bone to maintain blood Ca homeostasis. A prolonged period of Ca deprivation can lead to a weakened skeleton. In addition, this means that blood values of Ca are relatively poor indicators of Ca status in the horse. Calcium deficiencies are especially detrimental to young growing horses as this can lead to osteopenia. Improper ossification can lead to enlarged joints or improper growth patterns of the long bones. Therefore, it is critical to look carefully at the diet of lactating mares and foals.
Calcium requirements
Adult horses which aren’t exercising are relatively easy to meet their calcium requirements as can be seen in Table 1. The increase in Ca requirements for exercising horses is presumably due to an increase in bone deposition. Horses undergoing intense exercise experience an increase in bone mass and thus have a greater need for calcium. (More on bone formation in upcoming articles) It is unlikely that light exercise, or exercise that the horse is already adapted to (essentially no change in work intensity) results in much change in calcium requirements. Additionally most studies of calcium and exercise have focused on the young, growing horse. However, in an effort to err on the side of safety, the National Research Council recommends higher intakes of calcium. There is some loss of Ca in the sweat of exercising animals which is also represented in the increase in requirements for work.
Weight (lbs.)MaintenanceLight workModerate workHeavy work

Table 1. Calcium requirements (in grams/day) for adult horses at maintenance or work. To determine which class your horse fits into, read Energy for Work.


For gestating mares, requirements of Ca increase the greatest for the 9th, 10th and 11th month of gestation, which is concurrent with the most rapid increase in fetal growth. However, there is still substantial fetal growth in the 7th and 8th month of gestation as well, and so Ca requirements are greater than maintenance. Lactating mares clearly have an increase in Ca demand in order to support the very rapid growth of their foal. Mares fed an inadequate amount of Ca actually experience a decrease in bone density (as detected through radiographic analysis of the cannon bone). If you compare Table 1 with Table 2, you can see that at least in terms of Ca horses at light to moderate work would be considered to be comparable to gestating mares. However, demands of lactation far outstrip the working horses in needs of calcium. Therefore, one should either choose a feed for lactating mares and babies, or a supplement designed to meet their needs. After the first three months of peak lactation, the calcium demands on the mare taper off as the foal derives more of his nutrition from the feed he consumes.
Weight (lbs)Month of GestationMonth of Lactation

Table 2. Calcium requirements (g/d) for gestating and pregnant mares. Remember to use Table 5 from Broodmares and Babies to determine how much your mare should weigh.


The Babies
Obviously foals get much of their Ca from their mothers’ milk, but as they start to ingest new feeds and taper off their reliance on mom, it becomes your job to balance their diet. In the following table, I list the approximate Ca requirements of growing foals from 4 months until 2 years of age. Now, in just looking at the table, one might think that the Ca requirements appear low, but remember they are listed in grams per day! Because the foal is much smaller, he eats much less per day, thus the concentration of Ca in his feed must be greater. For example, a foal which consumed 2% of its body weight in alfalfa hay that was 2% Ca would meet its requirements, but if it was eating orchard grass hay that was 0.4% Ca would definitely not! There is not a very large decrease in overall Ca requirements as the foal matures. But as the foal matures and reaches a larger body size, it will consume more and thus the concentration of Ca needed in the diet will go down. Confusing, right? Don’t worry, next month we will discuss P requirements and then more importantly, how to put this all together with calculations from what you might be actually feeding.
Estimated Mature Weight4 mo-7 mo8-14 mo15-24 mo

Table 3. Approximate Ca requirements (g/d) for growing foals based on their estimated mature weight.

How big will my baby be?

How do you know what size they will be? Look at both the mare and the sire, and use an average. However, foals from maiden mares and older mares, tend to be smaller. Don’t forget that the nutrition program and environment that the dam and sire were subjected to also played a large role in their final growth. Also, foals carried by recipient mares will have a large influence in their size due to their foster momma, and less of an extent by their genetic mother. That’s why most farms choose larger mares for embryo transfer programs to carry donor mare’s babies. In addition, the early a colt is gelded, the larger they may mature to be. All in all, there is no firm way to know, but we can use our best estimation!

How much is too much?
Calcium has been fed as high as five times the horse’s requirement without any ill effects provided that the P intake is adequate. The maximal concentration of Ca in the horse’s diet is 2%, however it would be hard to find feeds that reach that level. However, excess Ca has been implicated as a causative factor of ulcers (See Is My Horse Stressed Out) due to an increase in gastrin secretion. Alternatively, others have found that alfalfa diets (and thus higher Ca) may decrease the incidence of ulcers. Clearly more work regarding Ca and ulcer formation in the horse is needed.
Osteopenia – a decrease in bone mineral density below normal. In humans this is considered to be a precursor to osteoporosis. Horses don’t really suffer from osteoporosis.
Ossification – essentially proper bone formation replacing cartilage as the horse grows, not to be confused with calcification. While calcification is a normal process of ossification, abnormal calcification can also occur, for example the formation of splints.

Gastrin – a peptide hormone secreted by the parietal cells of the stomach which stimulates secretion of gastric acids (HCL) and increases gastric motility. Gastrin release is stimulated by the presence of protein in the stomach, as well as conditions of hypercalcemia.


Minerals for Horses: Managing CA&P for Horses

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Written By Dr. Kris Hiney

Last month we took a more in depth look at the calcium requirements for horses. This month we will look at phosphorous needs in the horse, and then put it all together in formulating some diets for horses.


What does phosphorous do?
Many horse owners know that P is important for bone growth and skeletal health in their horses. While Ca is the major player, P makes up 14-17% of the mineral component of a horses skeleton. But that is not all it does. Phosphorous is vital in energy transfers (a little molecule called ATP – the P stands for phosphate!), DNA and RNA synthesis, cell membranes etc. Your horse would be going no where without P! Therefore, we shouldn’t forget P when looking at our horse’s diet.
What do you need to know?
For many horse owners, P is usually not to close to the forefront of our minds as most diets for horses will be adequate. However, the same is not true if you raise other livestock species. Phosphorous runoff is an environmental concern, and not something that even horse owners should completely ignore. Researchers have shown that high calcium diets may lower the ability of the horse to absorb P. This does not hurt the horse, as they are still absorbing a sufficient amount to meet their needs. But when we decrease absorption from the gut, you increase excretion in the form of feces. Now horse manure has a lower proportion of water soluble P in it compared to other species, and thus is less of a threat of contributing to run-off, especially in a pasture management situation. This may not eliminate the need for concern for larger stables with more concentrated numbers of animals. It may not be too long until the horse industry also comes under the scrutiny of the EPA. Now don’t panic! The point is that we simply want to avoid the random supplementation of minerals to horses without full consideration of the diet.
Phosphorous deficiencies and excessPhosphorous deficiencies are typically not seen in mature horses, even when exercising. However, just like with Ca, special attention needs to be paid to the broodmares and babies, who are both busy forming new bone! Certainly inadequate P results in a slowing of the growth rate of young horses, and can lead to improper bone formation.
However, excess P can be more of a concern. As stated last month, excess P can inhibit Ca absorption, which is why we always check the Ca:P ratio. Prolonged conditions of excessive P can lead to the development of secondary nutritional hyperparathyroidism. So what is the limit? Horses should not be fed more than 1% of their diet as P (and this is assuming a correct ratio). Typically this is not an issue unless the feed source is predominantly cereal grains (like wheat bran or oats) which are high in P. Conceivably this could happen on all grass forage (ie not legumes) with a high grain intake containing no mineral supplement as a balancer.
RequirementsAs the tables below show, maintenance horses will be fairly easy to meet their P requirements. In exercising horses, most of the requirements were determined using young horses who were also concurrently laying down more bone. However, again, the P requirements for mature exercising horses are estimated to be higher, more as a margin of safety.
Gestating broodmares and lactating mares again have higher P requirements, which you can see in Table 5. And just like last month, while the babies requirements might look low, they are listed in grams needed per day. That means that overall they need to have a higher concentration of P in the diet. Babies that are being fed for rapid growth without properly balanced P levels in the diet can certainly lead them to develop joint disease.
Weight (lbs.)MaintenanceLight workModerate workHeavy work

Table 4. Phosphorous requirements (in grams/day) for adult horses at maintenance or work. To determine which class your horse fits into, read ENERGY REQUIREMENTS FOR THE WORKING CLASS HORSE.

Weight (lbs)Month of GestationMonth of Lactation

Table 5. Calcium requirements (g/d) for gestating and pregnant mares. Remember to use Table 5 from BROODMARES AND BABIES to determine how much your mare should weigh.

Estimated Mature Weight4 – 7 month8-14 month15-24 month

Table 6. Approximate P requirements (g/d) for growing foals based on their estimated mature weight.

What’s in a feed
Before we start formulating some diets, it might be helpful to look at some typical feed stuffs that we use to create diets for horses. The following values are estimates only, and remember that forages grown on mineral deficient soils may have lower values. Typically, most grains are going to be higher in P than Ca. This should not pose a problem as concentrates should be fed to provide the extra energy or protein the horse needs, rather than making up the majority of their diet. The exception in the table is beet pulp, which isn’t a cereal grain at all. When looking at some typical hays, we can see that legumes (the alfalfa and red clover) provide much greater amounts of Ca than do the grass hays. This makes them ideal choices for broodmares and babies. Even most grass hays have Ca in the correct proportion to P, which makes feeding an imbalanced ratio hard to do. Note however, that orchard grass may be this exception.
Concentrate% Ca% P
Beet Pulp.89.09
Cracked Corn.04.30
Rolled Oats.11.40
Rice Bran.071.78
Wheat Bran.131.18

Table 7. Common concentrates fed to horses. All % are on a dry matter basis.

Forage% Ca% P
Coastal Bermuda.19.27
Brome Grass.29.28
Red Clover1.38.24
Orchard Grass.27.34

Table 8. Common forages fed to horses. All hays are assumed to be harvested at the midbloom stage. Remember that soil type as well as stage of maturity can alter your hays nutritional content.

Now, let’s put some of these numbers together. For simplicities sake, we will work with a generic 1100 lb horse, and then compare the numbers we get with the table values for different classes of horses. For our first example, we will feed this horse two different diets, one solely Bermuda Coastal grass hay, and one of alfalfa. We will feed him at 2% of his body weight per day. All values above are in dry matter, so we won’t have to convert those values.

First, we determine how much the horse will eat.
1. 1100 lbs x .02 = 22 lbs
Now remember all of our Ca and P requirements are in grams, so lets’ convert lbs to kg.
2. 22 lb x 1 kg/2.24 lbs= 9.82 kg of hay
So we know our horse will eat 9.82 kg of our hay per day.

For the grass hay, we will multiply the amount fed by the percentages of Ca and P in that hay.
1. 9.82 kg x 0.0019 =0.0187 kg of Ca
For that to make sense, convert kg into grams.
2. 0.0187 * 1000 = 18.7 g Ca
Now for P.
3. 9.82 kg x 0.0027 x 1000 g/kg = 26.5 g P
Finally, calculate your Ca to P ratio.
4. 18.7/26.5 = 0.71 to 1

So, what does this tell us? First of all, we probably need to have a mineral supplement for our horses to avoid the inverted Ca to P ratio. Alternatively, we could add some legume hay to its diet. When we look at simply meeting the requirements of our 1100 lb horse, we can see we are deficient in Ca if it is a working horse and certainly very low if that was all we fed to a gestating or lactating mare.

Now, what if we fed alfalfa hay instead? Use the same calculations, but insert the new % of Ca and P for alfalfa.
1. 9.82 kg x 0.0127 x 1000 g/kg =124 g Ca
Now for P.
2. 9.82 kg x 0.0024 x 1000 g/kg = 23 g P
Finally, calculate your Ca to P ratio.
124/23 = 5.4:1

Now we can see that our Ca to P ratio is more desirable. Looking at the horses’ requirements, we can see we have more than met the Ca requirement for all classes of mature horses, and are adequate for P for all working horses except those in heavy work. For mares, we are good until the last part of gestation and through lactation. That shouldn’t surprise you, as broodmares should be fed a better quality diet than our other horses.

Lastly, let’s see what happens if we decide to add 6 lbs of oats to this 1100 lb horse’s diet. Note: I am doing this solely for the purpose of calculations. There should always be some rationalization for why we add concentrate to our horse’s diet. For my mythical generic horse in this example, we don’t even know what class it is in or what its body condition score is.

For this example, we will change hays and feed red clover and orchard grass hays.
Let’s begin with the red clover.
1. 9.82 kg x 0.0138 x 1000 g/kg =135 g Ca
Now for P.
2. 9.82 kg x 0.0024 x 1000 g/kg = 23 g P
We will now calculate the contribution from our oats.
3. 6 lbs x 1 kg/2.24 lbs = 2.7 kg oats
4. 2.7 kg x 0.0011 Ca x 1000 g/kg = 3 g Ca
5. 2.7 kg x 0.0040 P x 1000 g/kg = 11 g P
Add the two values together for hay and oats
6. 135 g Ca from hay + 3 g Ca from oats = 138 g Ca
7. 23 g P from hay + 11 g P = 34 g P
Calculate your ratio
8. 138/34 =4.1:1

Looks good!!!

Now again, compare across our class of horses. Calcium is adequate for all classes, and our P requirements are met for all horses except the lactating mares.

Lastly, we will try adding oats to our orchard grass hay. 1. 9.82 kg x 0.0027 x 1000 g/kg =26.5 g Ca
Now for P.
2. 9.82 kg x 0.0034 x 1000 g/kg = 33.4 g P
Our oat values will remain the same as above.
Add the two values together for hay and oats
3. 27 g Ca from hay + 3 g Ca from oats = 30 g Ca
4. 33 g P from hay + 11 g P = 44 g P
Calculate your ratio
30/44 =0.68:1

Doesn’t look like something we should do!!!

To wrap up, remember that these diets were a simple exercise in calculating the contribution of calcium and phosphorous from different feed sources. These are not recommendations for actual diets, as we made no attempt to adjust amount fed, supplements added, or appropriate concentrates selected. Next month we will add in a more sophisticated approach to balancing diets inconsideration of type of horse, energy requirements, and growing horses. Until then, have fun practicing with your calculators!

 Make sure to check out Omega Fields horse supplements >>>

Minerals for Horses: Ca and P: Putting It All Together

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Written By Dr. Kris Hiney


Greetings again fellow horse owners! Hopefully everyone has had a chance over the last few months to start thinking about mineral requirements for horses in mathematical terms. To review, we have discussed the importance of Ca and P, especially in consideration of broodmares and young, growing horses. We have worked on calculating the Ca to P ratio you are providing in your diet, as well as comparing the total amount fed to the animal’s requirements. The suggested daily intake of Ca and P has been provided in tabular form, as well as some common feedstuffs’ concentration of these two minerals. Most importantly, we have worked out the math step-by-step, in order to allow you to really take a close look at your feeding program. This month we will more directly address the idea of feeding young horses properly.

Let’s talk babies!Again, review the last two articles which provided the amount of Ca and P that is needed by young growing horses. Compared to maintenance horses and exercising horses, the amount they need appears relatively small. But remember, their body size is also small, as well as the amount they can consume in one day! I think it is worthwhile to spend some more time specifically on this important class of horses. One of the difficulties in determining your young horse’s requirements is that they are usually listed according to their mature weight. Certainly that is how I presented this material in the last two months. But in order to help you out, the following table provides information on how much your young horse should weigh at various ages. This, of course is still according to their expected mature weight, which is at best an educated guess (See Minerals for Horses: Calcium). It is always important to monitor your foal’s weight gain, and determine if they are gaining excessive body fat. In addition, observe their joints carefully. Swollen and perhaps painful joints may indicate too rapid of a growth rate. For long term soundness, this is important to avoid.Table 1. Expected weights of young horses predicted by their expected mature weight. Note: these values would be typical of foals gaining weight at a moderate rate of growth.

Mature Weight (lbs)4 month6 month8 month10 month12 month14 month16 month18 month20 month
How much will Junior eat?Intake in young horses is varied, and certainly will be different due to feed availability, palatability of the feed, and competition between herd members. However, on average, young horses will eat between 2 and 3% of their body weight on a dry matter basis. So let’s assume we are feeding a 4 month old foal who will mature to 1100 lbs 2.5% of its body weight per day. We will feed him a mixed grass and legume hay that contain 1.09% Ca and 0.35% P. Now, let’s see if we are meeting his Ca and P requirements.The foal is currently 370 lbs. If he consumes 2.5% of his body weight that will be 9.25 lbs of hay per day. Let’s convert now to kg, remembering to divide by 2.24. Thus the foal is eating 4.1 kg of hay per day. Calculating by the percentage of Ca and P, this hay will provide 45 grams of Ca per day and 14 grams of P. Need a review? Revisit Part 2 in our series of minerals for horses. Now look at your tables. Our foal is meeting his Ca requirements but is 12 grams short of P. So what should we do? This is a situation where concentrate feeding is clearly warranted. So let’s select a suitable feed for our baby and recalculate.

We will adjust our feeding scheme to feeding our foal 1.5 % of his body wt as forage and 1% as concentrate. Feeding such a diet that s approximately 65% forage and 35% concentrate is fairly typical for young horses. Previously young horses were believed to need a much higher proportion of grains in the diet, but recent research has shed light on better strategies for feeding young horses. This diet will now provide 2.5 kg of hay and 1.7 kg of concentrate. The feed we select to use is designed for young horses and broodmares. It contains 1% Ca and 0.55% P. When we recalculate, this diet now provides 27 g of Ca and 9 g of P from the hay, and 17 g of Ca and 9 g of P from the concentrate. Added together, the foal is now receiving 44 g of Ca and 18 g of P. He is still a little bit shy in phosphorous, but I don’t want to add more grain to the diet. Alternatively, I could select a feed that provides slightly more P.

I decide to use a select a new feed which contains a higher percentage P at 0.7% while the Ca content remains the same. All figures would remain the same with the exception of the P contribution from the new feed is 12 g of P. We have reached our goal of feeding our new guy a balanced ration (at least in terms of Ca and P)!

Now, for the sake of argument, let’s try to formulate a new ration that relies on slightly less grain for our growing foal. We will feed 2 % of his body weight in hay, 0.5% in concentrate and add a mineral supplement. The mineral supplement I chose has a concentration of 13% Ca and 12% P. It is designed to be fed at the rate of 2-4 oz per day. We will feed our baby 2 oz of the supplement per day.

Hay : 3.3 kg/day (2% of his body wt)
3.3 kg x 1.09% = 36 g Ca
3.3 kg x .35% = 12 g p

Grain: 0.8 kg (0.5% of his body wt)
0.8 kg x 1% = 8 g Ca
0.8 kg x 0.55% = 4.4 g P

Mineral supplement: 2 oz per day
Note: There are 28.35 g per oz. Therefore this colt will receive 56.7 g of supplement
56.7 g x 13% = 7.4 g Ca
56.7 g x 12% = 6.8 g P

All together the diet now provides 51 g of Ca and 23 g of P. This meets both his Ca and P requirements while allowing you to feed a more forage based diet. Now, which should you do? Well, that’s a topic for an entirely new discussion!

Next month we will continue on with minerals, but discuss one of the most confusing, miscalculated minerals there is – selenium. Until then, happy horse feeding!


Minerals for Horses: Demystifying Selenium

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 Written By Dr. Kris Hiney

Selenium is an often talked about micro mineral which has much confusion over its requirements. Certainly those in the nutrition field don’t make it any easier by listing the requirements in concentrations in the diet, where all other minerals are simply listed as the amount the animal should consume per day.

Selenium is an essential mineral that is integral to the enzyme glutathione peroxidase (GSH-PX). GSH Px is a powerful anti-oxidant which helps protect cell membranes, proteins and even DNA from reactive oxygen species such as peroxides, free radicals etc. The enzyme GSH-PX acts by donating an electron and thus reducing these reactive compounds. Less commonly known, Se also serves a role in thyroid metabolism. Selenium is a part of the enzyme thyroid hormone deiodenase, which serves to convert thyroxine (T4) to its more biologically active form, triiodothyronine (T3). Thus Se deficiency can play a secondary role in hypothyroidism.

Selenium is also a confusing mineral because it is more or less of a problem depending on the area of the country you live in. Areas of the country which typically have higher Se concentration in the soil include South Dakota, Montana, Wyoming, Nebraska, Kansas, Utah, Colorado, and New Mexico, while the Great Lakes region, the Northwest and the Southeast are considered Se deficient. The more alkaline or basic the soil, the higher the concentration of Se in the plants that grow there. Dry conditions will also encourage the plant to uptake more selenium, which further increases the Se concentration. High selenium concentrations in the soil can be detected by the abundance of indicator plants, which include locoweed, milk vetch, woody aster and false goldenweed. During drought conditions horses will also be more likely to consume plants they may not eat normally. Therefore it is important to closely monitor pastures for horses during dry conditions.

Se and your calculatorSo let’s talk numbers and get to the heart of the matter. The Food and Drug Administration regulates the amount of Se that can appear in swine, cattle and sheep feeds due to these animals typically entering the human food chain. For traditional livestock species, Se can only appear at a level of 0.3 mg/kg DM in complete feeds. That would be the concentration of the entire diet the animal consumes, not just the individual components. It is much more common in the livestock industry to feed complete rations or TMRs – total mixed rations. In horses, with the exception perhaps of complete feeds that many senior horses consume, we tend to feed forage with grains or some other type of supplement Even further, the total amount of Se beef cattle can consume per day is only 3 mg. This is according to Title 21, Part 573.920 in the Code of Federal Regulations. These regulations however, do not hold true of equine feeds.So what is actually the requirement of Se for the equine? Currently the recommendation to meet the horse’s nutritional requirements is to feed at 0.1 mg/kg or 1 mg/d. However, there is some evidence that feeding at rates of 3 mg/d may improve antibody status and overall immune function in the horse. No evidence exists that feeding at a rate of higher than 0.5 mg/kg in the total diet would be beneficial to the horse. Alternatively, there is also some pushback from environmentalists to reduce the level of Se in animal diets to only meet their requirement. They are encouraging the FDA to alter the current legal level of Se back to only 0.1mg/kg in the attempt to limit any Se accumulation in runoff etc. However, the contribution of Se from livestock feed is quite small compared to that produced through fuel combustion, industrial uses and leaching of selenificious rocks.

When we look at complete feeds for horses they typically contain between 0.3 – 0.5 mg/kg or ppm. A quick scan across commercially available equine feeds reveals a typical concentration of 0.3 mg/kg with some feeds slightly higher. In comparison, the Feed Additive Directive in the European Community allows Se to appear maximally in a concentration of 0.5 mg/kg. So how much Se would a normal horse on a complete feed consume? Let’s use a 500 kg horse for simplicities sake (that would be 1100 lbs). Typically we would assume the horse can eat 2% of its body weight per day. At an intake of 10 kg per day of a feed which contains 0.3 mg/kg, the horse would consume 3 mg of Se per day. So clearly horses can tolerate this rate of consumption quite well.

Signs of deficiency of Se in the horse general include disorders of the muscle or myopathies. This can include muscle weakness, gait abnormalities, respiratory distress and cardiac impairment. Foals born with a Se deficiency may have difficulty in nursing. Traditionally Se and/or Vit E deficiency disease is termed as white muscle disease. Numerically, serum Se less than 60 ng/ml or a GSH-Px concentration of less than 25 EU/dl can indicate a Se deficiency. However, these numbers are not indicative of a deficiency unless other clinical symptoms are present. Clearly much still remains to learn of Se metabolism.

Toxic Se?But what is considered a toxic level of Se and why are we so concerned with Se toxicities? The upper safe margin for horses is suggested to be at 2 mg/kg. That is essentially a single decimal point in difference when calculating rations. Now using our same horse, and assuming he still eats 10 kg, the horse has now consumed 20 mg of Se. This is a much narrower margin of safety than any other nutrient we include in the diet. Now remember, that is the total concentration in the diet, not of individual ingredients. Symptoms of acute Se toxicity include blindness, head pressing, sweating, colic, increased heart and respiration rate and lethargy. Chronic Se toxicity caused hair loss, especially of the mane and tail, and changes in the hooves leading to soreness, including cracking of the hoof below the coronary band. Most are familiar with the recent story of the polo ponies who all died after receiving a Se injection from the team veterinarian. Ironically, anecdotal evidence already existed that administration of injectable Se and vit E may cause anaphylactic shock. This is probably due to the carrier agent used and not the concentration of Se or Vit E.The form Se is in may also play a role in toxicities. Se that appears within amino acids (such as would be found in plants) is much better absorbed and thus may reach toxic levels more quickly. In plants, Se is found in the form of selenocysteine, selenocystine or selenomethionine. Inorganic sources of Se include sodium selenite and sodium selinate. While some studies have reported no difference in bioavailability, (essentially the rate at which a substance enters the circulation) others indicate that selenium from yeast sources results in a greater detected increase in tissues and blood. While there is evidence on both sides, many have moved to using an organic source of Se in feed. Thus diets that contain Se in the form of Se yeast can’t have more than 0.3 mg/kg of Se in the total diet.

Now let’s look at some feeds and determine their contribution of Se to the diet.

A loose mineral supplement that contains 35 ppm of Se and is fed at 2 oz. per day compared.
Or one which contains 15 ppm at 2 -3 oz per day.

First, we need to know that 1 oz is equivalent to 28. 3 grams. If we feed our horse 2 oz. per day, that would be equal to 56.6 grams of supplement. If Se is listed in ppm or mg/kg, we simply convert units. There are 1000 grams in a kilogram, so our horse is eating 56.6 g/1000 g/kg or 0.0566 kg of supplement. Now multiply that by our Se concentration. In our first supplement, 35 mg/kg * 0.0566 = 1.9 mg of Se. That is right in the middle between the Se requirements for the horse and the higher level of intake that has been shown to have beneficial effects. The supplement which contains 15 ppm would provide between .8 and 1.3 mg of Se depending on if you fed 2 or 3 oz of the feed.

So until next time, don’t panic about Se, now you know how to feed it correctly!


Minerals for Horses: Supplying Electrolytes To Your Horse

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Written By Dr. Kris Hiney

Last month we discussed the function of electrolytes and some special disorders of horses related to these minerals. This month we will look at how much of these minerals your feed usually supplies, and determine how much electrolytes you may need to try and supplement to your horse.

How much do they need?Overall, the diet of the horse should contain between 0.25-0.5% salt. So, for example, let’s assume we have a 500 kg horse that eats 2% of his body weight per day. In total, he would consume 10 kg of feed per day. If we use those ranges of intake listed above, he should be ingesting between 25 and 50 g of salt per day. Therefore, the minimum a maintenance horse should be ingesting is about 25 g of salt per day. This will provide sufficient sodium and chloride for the horse. If we look at some typical hays for horses, the sodium content is quite low. Let’s just pick one and do the math to see how it works out. If we use the generic cool season grass hay, feeding 10 kg of this hay per day would supply 8 grams of sodium, 213 g of K, and 92 g of Cl.

Table 1. Average values on a percent basis for sodium, potassium and chloride for four general types of hays.

Types of HaysSodiumPotassiumChloride
Coastal grass0.171.800.67
Cool season grass (mid maturity)
Legume (mid-maturity)0.022.450.61
Mixed legume/grass0.012.801.10

Table 2. Sodium, chloride and potassium requirements for different exercise classes of a 500 kg horse in grams/d.


Comparing this to the maintenance horses requirements listed in table 2, tells us that the horse really needs to only get extra sodium. In fact, only the heavily exercising horses will probably need additional chloride supplied to them. Again, this is heavily dependent on the temperature in which the horse is working.

What about grain?Many horses also receive a concentrate in addition to the forage they are eating. Typically, most horse feeds are formulated to contain between 0.5 and1% salt. This increased concentration of salt in the feed is based on the knowledge that most horses will be consuming less grain then hay. Let’s use our same horse above, and now feed him a diet that adds 5 lbs of grain per day. (Wondering how much hay and grain your horse should be eating? See Rules to Feed By) I’ll convert back to kg so that we can look at our numbers on a gram basis. 5 lbs of grain is equivalent to 2.2 kg. If we assume our grain has 0.5% salt in it, then it supplies 11 g of salt. That breaks down to about 4 g of Na and 7 g of Cl (salt is 39.3% Na). Therefore, your concentrate may be helping to meet your horse’s salt needs. However, the tricky part is that the salt concentration is typically not listed on the feed tag, so you really don’t know how much it is supplying (See Using Feed Tags). Therefore, to be safe, you should supply your horse with some sort of salt source in addition to his feed. If you look at most feeding guidelines for equine feeds this is why it is stated to also supply your horse with salt on a daily basis. Take for example Omega GRANDE. A one day serving for horses is 227 grams. For the horse to consume it’s minimum amount of salt, Omega GRANDE would have to be 11% salt if it was to serve as the sole salt provider! And that would be just for a maintenance horse. Horse will not consume feeds with high concentrations of salt, and salt addition can even be used in some livestock species to limit feed intake. Consider that many horses really don’t need to be eating grain to begin with, or at least a reduced amount to avoid obesity, supplementing salt is always a necessity.
Providing salt

Since we know that typically feeds alone won’t meet our horse’s needs, (or we may not really know what they are supplying), the easiest way to meet the horse’s needs is to supply a salt block. Researchers have shown that on average horses willingly consume about 50 g from a salt block per day. However, the variability in intake is high. Individual horses may range between 9- 143 g of salt per day! Therefore, some horses will eat too much, while others not enough. Even the same horse may alter his intake of salt quite a bit from day to day. If you really like projects, and have a sensitive scale at home, you could determine your horse’s average salt intake per day (if he is kept alone with his block) by weighing it every day. Also, some horses just won’t eat their block. If your salt block shows no evidence of licking and is covered with dust, you have a non-licker. Alternatively, you could try to provide loose salt, which some horses prefer or specifically feed salt to your horse. So how much salt should you provide your horse per day, especially if he is a non-salt block licker? For your maintenance horse, that would be about 1 oz. which is 28 grams. If you prefer to use your teaspoons to measure instead, one teaspoon contains 6 g of salt. So your horse would need 4 teaspoons of salt per day.

Exercising horses

A horse in heavy work requires about twice the maintenance amount, or about 50 grams of salt per day. However, for those intensely working in hot climates, some researchers have indicated their need for electrolytes may increase 9 fold. Now remember, these are probably the race horses, three day eventers etc. Obviously for the exercising horse in hot climates, they may not be able or willing to consume that much via their salt block, which is why it is important to look consider supplementing your horse. Now remember, these horses would probably be consuming more grain than our example horse above, due to the increased energy demands placed on them. Therefore, you may presume that they are taking in much more salt in the diet. If you are supplementing your horse with table salt, you would increase that amount from maintenance to 2 oz or 8 teaspoons (2 2/3 tablespoons), with an increase to 3 oz or 12 teaspoons (4 T.) in hot climates. There are also many commercially available electrolytes as well which can be added to water or provided in a paste form.

Getting the water back inTypically if you need to provide a horse with electrolytes, you should also be concerned with rehydrating the horse. Oddly enough, the horse’s own system can work against it. As the sweat of horses is so much more hypertonic (or contains more solutes) than its plasma, when horses sweat heavily, their blood becomes hypotonic. It does not provide the normal stimulus to drink that having a higher electrolyte concentration in the blood does. Therefore, even if offered water, your horse may not drink. Providing electrolyte pastes or saline solutions after exercise may cause the horse to restore his water balance and recover more quickly. However, do not just offer a horse a salt water solution if they have not been trained to drink it. This will result in water refusal and only exacerbate the problem. They should also be offered a choice of non-saline water to ensure that they replenish the water they have lost. In addition, horses seem to prefer tepid water to ice water when given a choice. So remember, it is as imperative that the horse is also restoring his water balance after exercise as it is to provide electrolytes.Next month we will look at two very important trace minerals, copper and zinc.


Minerals for Horses: Copper and Zinc

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 Written By Dr. Kris Hiney

This month we will discuss two important trace minerals, copper (Cu) and zinc (Zn). We will discuss them together, as they are most commonly discussed in relation to developmental orthopedic diseases in young horses. First of all, copper and zinc are classified as trace minerals because they are required in far less quantities compared to Ca, P, Na, Cl etc. While the minerals we previously discussed were described in terms of percentages of the diet, or in grams, trace minerals are only required in mg per day. Typically their requirements are listed in ppm (or mg/kg) of the total diet. It is then assumed that a horse would be consuming a standard 2% of their body weight per day. Thus if a requirement is listed as 15 ppm, then a 500kg horse should consume 150 mg per day. Now let’s discuss what these particular trace minerals do for your horse.

Cu and its functionsCopper is a mineral that is heavily involved with collagen and elastin and their tissue integrity. Collagen is a structural protein found in skin, tendon, arteries, bone and cartilage, while elastin is found primarily in ligaments. Copper is necessary for a key enzyme (lysyl oxidase) which catalyzes the cross-linking of collagen, and thus is vital for the strength of cartilage, tendon etc. Essentially that is the connection between separate collagen fibers. That is why Cu is typically implicated in developmental issues in growing horses. Copper also plays a role in energy production as it is part of cytochrome c oxidase, an enzyme which transports electrons and helps to generate ATP (remember, that is the energy currency for cells) within the mitochondria. It is also necessary for iron (Fe) metabolism and serves in an anti-oxidant capacity. Copper easily accepts electrons and thus aids in scavenging free radicals. In fact, free Cu can actually cause free radical damage due to its ability to “grab” electrons. Thus in order to protect body tissues, Cu is found in blood bound to the protein ceruloplasmin. Both Cu and Zn are associated with the enzyme superoxide dismutase, a main player in preventing oxidative damage. The superoxide radical (oxygen with an extra electron) is one of the main reactive oxygen species (it steals electrons away from other molecules and makes them unstable) and can cause tremendous damage to the body unless it is eliminated. Superoxide dismutase catalyzes the reaction of two superoxide radicals to create hydrogen peroxide and oxygen. Finally Cu is involved in the enzyme tyrosinase, which catalyzes the production of melanin. Without melanin, hair loses pigmentation and can create funny colored animals!

Figure 1. Collagen is made up of several types of proteins. These proteins are wrapped around each other in a helical structure. The crosslinks between separate collagen molecules help to provide the stability in equine tissues such as cartilage, tendons etc.

Are horses different than other animals?Copper metabolism in horses differs from other species, so direct extrapolation from studies in other species may offer incorrect assumptions. For example, ruminants can suffer Cu deficiencies if fed a diet high in molybedenum. However, this does not happen in horses. In other species, alterations in hair coat due to Cu deficiency also appear more rapidly. In horses, only anecdotal evidence (never reported in trials where Cu deficiencies are achieved deliberately) supports the idea that the horse’s hair coat will differ (most often reported in black horses). And remember, sun can bleach hair coats and create a dull, reddish tinge too! Horses don’t show as extreme sensitivity to Cu overloads as well (sheep are especially susceptible) and can tolerate concentrations in the total diet as high as 250 ppm. Therefore, information concerning Cu and its metabolism, and requirements, needs to originate from equine trials.
Zn and its functionsZinc is a ubiquitous mineral involved in over 100 enzymatic actions in the body. Key functions include digestive enzymes, bone function, and immune function, as well as the previously mentioned role as an anti-oxidant. Ironically, Zn may actually prevent free radical formation caused by other metals (primarily Cu and Fe which are highly reactive). When Zn is incorporated into proteins vs other metals, it may decrease the overall generation of free radicals. In humans, marginal zinc deficiency results in impaired taste and smell, as well as memory loss and decreased male fertility. In its anti-oxidant capacity, Zn helps to maintain cell membrane integrity, which may contribute to its immune function as well. Zinc deficiencies in animals and humans results in decreased resistance to pathogens (viral, fungal and bacterial) and even parasites and decreased antibody formation. The immunologic function of Zn is why it is commonly available in cold lozenges for people (it was clinically proven to decrease duration of the common cold). Currently no such studies have been conducted in the equine.
The role of Cu and Zn in bone disordersDeficiencies in Cu especially have been implicated in developmental orthopedic diseases in young horses. This term can encompass such disorders such as physitis (inflammation of the growth plate), flexural limb deformities, wobblers (compression of the spinal cord in the vertebrae) and most commonly osteochondrosis or OCDs. It is also commonly referred to osteochondrosis dissecans once a flap of cartilage is free floating in the joint. Osteochondrosis is typically seen as a lesion in the cartilage due to improper ossification of the subchondral bone (bone underlying the cartilage in a joint). Management of young horses including diet and exercise, rapid growth rate, as well as genetics have been implicated as causes of these disorders. Experimentally, cartilage lesions and gait abnormalities were induced in foals fed a diet deficient in Cu, but these foals were also deficient in Ca and P. Thus the absolute cause is difficult to tease out. Unfortunately subsequent studies in foal development and Cu intake have had contradictory results. Overall the most benefits in Cu supplementation in preventing OCDs may be realized by supplementing the dam in late gestation. A Cu deficiency may not result in formation of OCDs (genetics, growth rate, other nutritional factors may actually cause the lesion development) but Cu may help in the repair mechanism. Visually, it may be difficult to determine if foals are deficient in Cu as their growth rate and outward appearance is normal. On a practical note, while Cu concentrations have been increasing in commercial equine feeds, especially in feeds formulated for young horses, a decrease in OCD have not been seen generally in the equine population. Now certainly, there are many confounding factors in the pathogenesis of OCD, genetics included. In the equine industry, we are guilty of breeding horses despite them having soundness issues. Thus, we may be inadvertently perpetuating developmental diseases in our horses.

Figure 2. Alterations in the normal process of ossification can result in cartilage defects.

Cu and Zn requirementsIdeally mature horses should receive a total diet of 10 mg/kg or 0.2 mg/kg BW/d. Therefore a 1100 lb horse which consumes 2% of its body weight in feed per day would consume 100 mg of Cu per day. Most natural horse feeds contain 3-20 ppm of Cu. Increases in Cu requirements due to exercise are slight, and most will be accomplished simply by increasing intake to meet energy demands. Current recommendations for Zn are to be fed at a rate of 40 mg/kg DM. Thus depending on the feed source of the horse, supplementation becomes more necessary. Typically mares fed a normal diet should supply adequate Cu in the milk for foal growth as no additional increases in milk Cu concentration were seen with Cu supplementation to mares. However, as a precautionary measure an increase in Cu in the diet of broodmares may be warranted. Feeds designed to be fed for foals often contain 50 ppm of Cu or greater and between 150 to 220 ppm Zn. These values are well above the current NRC recommendations as more of a safety precaution. However, overzealous supplementation of trace minerals is not a wise idea. Excess Zn can impair Cu metabolism as they share a common transport mechanism. Typically this wouldn’t be an issue unless Zn concentrations are over 200 ppm in the total diet. This might occur with a misformulation of a diet, or if the horses are pastured need a metal refinery. It is recommended for Zn to not reach a concentration over 500 ppm. Extreme levels of Zn can cause joint abnormalities but only in excessive quantities (such as 2% of the diet).

Figure 3. The cartilage defect in the hock joint is circled in red.

Next month we will discuss Mg and Fe.

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Minerals for Horses: Magnesium and Iron

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 Written By Dr. Kris Hiney

This month we continue on our path of discussing minerals required by horses. We will actually be mixing a macro-mineral (magnesium) and trace mineral (iron) together. However, our goal has been to visit minerals in the order of their level of concern by the horse owner and their frequency of need for supplementation.

Function of MagnesiumMagnesium is an important mineral involved in many enzymatic reactions (as so many of the minerals are). The largest store of Mg in the body is in bone (60%), with a relatively small amount present in the blood. Magnesium also acts as an electrolyte as well and therefore is essential for normal nerve and muscle function. Magnesium is a key component in enzymatic reactions involving the synthesis of nucleic acids, protein, carbohydrates and lipids. Magnesium and ATP are almost always found complexed together in the body. In all, Mg is involved in over 300 enzymatic reactions.
Mg requirements Most equine feeds contain Mg in a range between 0.1 to 0.3%. If we use our average horse of 1100 lbs (500 kg), that horse would receive between 10 and 30 g of Mg per day if he was consuming 2% of his body weight per day. Remember, that is our normal goal for feeding. Currently the recommendation for Mg intake for a mature horse is 7.5 g of Mg/d for a 500 kg horse, or 15 mg/kg of body weight per day. Therefore, most horses easily meet their Mg requirements by consuming their regular diets. For young growing horses, the requirement on a percent of their body weight is higher (approximately 21 mg Mg/kg), due to their need to accumulate Mg in growing tissues. As their growth rate tapers off, the concentration of Mg in their diet can be lowered. Pregnant mares do not actually have a much higher Mg requirement than a maintenance horse, and suggested to only be 15.3 mg/kg of body weight per day. Therefore mares should easily be able to consume that amount. For example a 500 kg mare would need 7.7 grams of Mg per day. Only 200 mg more than our maintenance horse! From our above description of the normal Mg content of feeds, this would be easily obtainable by the mare simply eating 2% of her body weight. Remember if allowed, mares will consume much more feed than this! Once our mare has foaled and begins to produce milk, her requirements will increase in order to support her growing foal. During peak lactation she will need 22.2 mg of Mg/kg of body weight or 11.1 g total for that 500 kg mare. Again, this is probably easily obtainable unless she is consuming a marginally deficient diet.Now let’s shift our focus to the exercising horse, who we would expect to have a greater Mg requirement due to sweat losses. To account for changes due to sweating, assume an increase in consumption of 1 – 2 g per day, depending on sweating rate, for a light to moderately exercised horse. If the intensity of the exercise increases and thus the accompanying heat load, the requirement of Mg is suggested to double. Therefore, for those 3 day eventers or endurance horses, they should receive 30 mg/kg body weight or 15 g of Mg per day. It is possible for these horses on a normal diet to end up being deficient in Mg. In several studies in young growing exercised horses, it appeared bone Mg deposition was greater when horses were fed diets higher than previously recommended in Mg. However, in these studies, horses were also fed more Ca which may have led to greater bone formation and thus the accompanying increase in Mg retention. However, because of this interaction between both exercise and growth in the young horse, the Mg requirements of these horses should be treated more like an intensely exercised horse, or 30 mg/kg body weight.
Magnesium deficienciesTypically, acute Mg deficiencies in horses are quite rare, compared to the relatively more common occurrence in cattle. In horses, Mg tetany (or a bout of muscle contraction causing locking of the muscles) has occurred in stressed horses (typically transported) and in lactating mares. Presumably in transported horses, there would have been increased Mg losses in feces (increased intestinal motility while being nervous) or through sweating. In mares, a loss of Mg in milk while on a Mg deficient diet would contribute to an acute Mg deficiency. Rapidly growing pastures are typically low in Mg and high in K may be a risk factor in Mg deficiency, but this is much more of a concern for cattle than for horses, which absorb Mg more efficiently.Some individuals have suggested that magnesium should be supplemented to horses presumed to have insulin resistance. Magnesium does play a role in insulin release by the pancreas and its activity. This idea presumably originates from data in humans. Frequently those with type II diabetes (25-35%) have lower serum magnesium levels than those without the disease. The hyperglycemia associated with type II diabetes may result in increases loss of Mg through the kidney. It is not known if the hypomagnesia is a consequence or a potential cause of type II diabetes and insulin resistance. Studies in humans using Mg as a potential treatment of type II diabetes and insulin resistance have yielded conflicting results, with some having positive results and some with no change in insulin and glucose homeostasis. To date, no such studies have been performed in horses.
Function of IronIron (Fe) is most commonly known for its role in hemoglobin and oxygen transport. It is also a very important ion in the electron transport chain, carrying electrons in order to produce ATP. Thus it is integral in body function. Most equine feeds range between 100-250 mg of Fe/kg of feed. Grains may be lower than forages. Iron absorption in the diet is highest in newborn animals, and also in animals that are fed Fe deficient diets. The body simply becomes more efficient out of necessity and therefore absorbs proportionally more of the iron in the diet.The quickest observable sign of iron deficiency is anemia. Ironically, most animals will never be deficient in iron if they have access to soil. So horses grazing pastures should be adequate in Fe status, but horses which are continually stalled may be at a higher risk of Fe deficiency. Supplementation of Fe has been unable to show any change in hemoglobin or the oxygen carrying capacity of the blood, and therefore may be unwarranted in horses fed normal diets. Over supplementation of Fe has been reported, with clinical signs of iron toxicity disappearing after withdrawal of the supplement. Horses in this study were being fed 0.6 mg/kg Bw/d of ferrous sulphate. Thus owners should be careful about being too enthusiastic in their supplementing regimens. However, others have found no ill effects from feeding horses 500 and 1000 mg/kg feed although serum and liver Zn were reportedly lower. Supplemental iron may be toxic to young foals due to their greater efficiency of absorption. Even when fed at the rate of manufacturer’s suggestions for adult horses, death can quickly result.The requirements for iron in the mature horse are estimated at 40 mg/kg DM and 50 mg/kg for young foals, pregnant mares and lactating mares. For our 500 kg horse, then they should consume 400 mg of Fe per day. Remember when nutrients are listed on a concentration basis, it is assumed that the horse would be consuming 2% of their body weight per day. If our horse was eating 10 kg of feed ranging between 100 and 250 mg Fe/kg, he would receive 1000 to 2500 mg of Fe per day (or 1 – 2.5 g) of Fe. Again, most horses do consume adequate Fe. In a fairly recent study looking at blood mineral profiles, the Fe status of horses with pica (consumption of unusual objects including soil) was lower than in horses who did not perform this behavior. That would make sense as soil does indeed provide the normal grazing horse (they pick up soil inadvertently as they eat) with additional Fe. Therefore, if your horse is performing this behavior, it might be advisable to examine his diet more closely.

Remember, the temptation of most horse owner’s is to over supplement their horses. However, this is often unwarranted, contributes to the expense of managing the horse, and may provide no benefits to the animal. Certainly overzealous supplementation may actually be harmful to the horse.

Key terms:Hypomagnesia – lowered blood levels of magnesiumHomeostasis –physiological ability to maintain an equilibrium through an interaction of complex relationships. For example, glucose homeostasis is an interaction between key organs (liver, kidney and pancreas) and the hormones (insulin, glucagon, cortisol etc)to keep glucose at a relatively constant levelNext month: We wrap up the left over minerals! Manganese, cobalt, chromium and iodine

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