VITAMINS: Exciting? No. Necessary? Yes. 

In the past several months we’ve covered the roles of water, protein, fat, and carbohydrates in the horse’s diet. This month we’re looking at vitamins and next month we’ll talk about minerals. Ugh, right? Not the most exciting topic. We think a lot about water (or we SHOULD be) and we pay attention to protein and we fret about fat and carbs. But vitamins and minerals…yeah, they’re in the feed, sometimes we wonder if we should supplement, but they don’t usually occupy a lot of brain space. They’re just sort of…there. Right? Let’s see if we can have some fun with this topic though and learn something as we go along.

I’m not going to tell you how much you should be feeding your horse. That is a discussion to have with your veterinarian, as each horse is an individual and should be fed as such. Your horse’s need varies depending on age, job, environment, diet, and health. The topics we’ll look at in this article and next month’s article are what the vitamins and minerals do, where they are found, and what happens if your horse eats too little or to much of them. Just as too little can be harmful to health, adding too much isn’t good either. More isn’t always better.

I’m also not going into great depth with each of the vitamins and minerals. With a nod to equine nutritionists and researchers, one could write pages and pages for each vit and min. One could spend hours researching and reading about the role of each. Some haven’t even been studied that much, and in some cases the daily requirements for the horse have not yet been established. My goal is just to keep you interested and help you with the basics.

Here’s the thing about vitamins and minerals: a little bit goes a long way. I suppose you could think of them as super-concentrates. We talk about the horse’s need for gallons of water, pounds of fiber, even pounds of carbs and protein, but vits and mins? The horse needs ounces, or maybe not even that much, in his daily diet. You can see this just by looking at the feed tag, which we’ll do later. I’m not trying to scare you here, but not providing enough ounces- or too many ounces- can be a big deal.

How can you tell if your horse isn’t getting enough, or is getting too much? There may be physical signs that you can observe in your horse’s behavior, muscles, teeth, hooves, hair, performance, and overall health. That isn’t definitive though. The best way to determine is to talk with your veterinarian, who will probably recommend a lab test. Keep in mind that if your horse is deficient in vitamins and minerals or has a toxic amount in his body, it can take time to clear this situation and get him “right” again.

So how can you make sure your horse is getting the correct amount? It’s actually not that hard. If you are feeding a commercial feed and you are following the recommendations on the bag, your horse is likely in the safe range. Same thing if you are feeding a ration balancer and following the feeding guidelines. Remember, this means feeding by the pound, not by the scoop, or the handful, or “just a bit.” If you have your hay analyzed, then you have even more useful information.

Let’s look at a few definitions to set the stage. Vitamins are organic substances. That doesn’t mean “organic” like the high-priced veggies at your local supermarket. Organic means that they are produced by animals and/or plants, which are living organisms. Minerals are inorganic and come from the soil or may be dissolved in water. They may be absorbed by the plants that your horse eats, but the plant doesn’t produce them. Without being too technical, the main difference between organic and inorganic is that organic nutrients (protein, fats, carbs, vitamins) all contain carbon. Inorganic nutrients, such as minerals and water, do not contain carbon. Although water can carry carbon, it isn’t part of the chemical composition of water. (An extra cookie for you if you remember the molecular formula for water!)

Now this paragraph is not related at all to today’s discussion, but it’s kind of cool. Four years ago, I visited relatives in Alaska. We were in a part of the state with incredibly high amounts of the mineral silica in the soil. There is a certain type of grass that takes up so much silica that it looks crystallized- as if one had dipped it in clear glitter and let it dry. It was beautiful, very brittle and abrasive- nothing that a horse would want to eat! In fact, I didn’t see signs of anything, including insects, eating this grass. It didn’t grow very tall either, partly because of the short growing season and probably because the huge amounts (and weight) of silica in the plant tissue didn’t leave much room for many other nutrients. A rather extreme example of how plants can take up minerals, certainly, but fascinating and rather pretty in a bizarre way.

A vitamin or a mineral might be found in different forms, and this matters because some forms are more bioavailable (easily digested) by the horse than others. Some can actually be manufactured in a laboratory. Generally, it’s thought that the naturally produced versions are the better choice. An example of this is magnesium. Feed manufacturers have several forms to choose from! The choice is driven by cost and digestibility. The more digestible, the higher the cost, of course. Adding more of the cheaper stuff doesn’t necessarily mean the horse gets more of the mineral either. In fact, it can lead to the blocking of digestion of other minerals. It turns out that the proportion to other minerals, not just the amount, can be key.

When you’re looking at the feed bag, trying to determine the vitamin and mineral content, look at the ingredients too. That will give you some insight into the source of the vits and mins. You may see the term “chelated,” which means that the mineral is bound to amino acids and peptides, which are the building blocks of protein. These are sometimes called organic minerals, not because their source is organic but because they are tied to an organic molecule of amino acids. They are believed to be more bioavailable than inorganic minerals.

I don’t want you to sound like a total rube when you’re having in-depth discussions about equine nutrition with fellow horse friends at the local coffee shop. (You do that, right?) It’s pronounced “key-lated,” NOT “che-lated.” That’s right, with a “k” sound. It derives from the Greek word “chela,” meaning claw. Go figure.

Vitamins are grouped into two categories. There are fat-soluble vitamins, which are A, D, E, and K. These can be stored in the horse’s body and used later as needed. Because they are stored though, there is the danger of toxicity if the horse eats more than he can use over a period of time and is unable to flush them from his system.

Vitamins B and C are water-soluble: they are not stored in the body. Excess leaves the horse’s body in his urine and manure, and there isn’t much concern about toxicity because the horse doesn’t store them.

Let’s take a quick look at each vitamin. Again, this isn’t a definitive guide- you could probably find pages of information on each if you wished. The goal here is to show you the sources and to touch on the reasons why they are important to your horse’s health.

Vitamin A is found in fresh grass and good quality hay. The horse can store excess in his liver for those months when pasture isn’t available. Vitamin A supports eye health, especially night vision, reproductive health, and the health of bones, skin, and muscle. Too little of it can lead to eye problems including tearing and night blindness, problems with reproduction, defects in bone and muscle, a dull coat, and increased risk of infections. Interestingly, too much can display the same symptoms plus weight loss and neurological problems. Excess is usually due to giving too much as a supplement, as the amounts found in forage aren’t enough to be toxic.

Vitamin D is made by the horse’s body, in his skin, when he is exposed to sunlight. It can also be found in forage and hay, but it decreases during storage over the winter. The horse can store it in his body for those months of reduced sunlight. In young horses, it is very important for skeletal growth. In mature horses, it helps to regulate the calcium and phosphorous levels. Too little can lead to bone deformities. Too much leads to stiffness in joints and muscles. In extreme cases, too much can lead to calcium deposits on internal organs, and even death.

Vitamin E is found in fresh grass and hay. Alfalfa tends to have more than grass hays. Vitamin E does not store well though and it degrades quickly in stored hay. In fact, some recent studies seem to indicate that it breaks down within days of curing the hay. It is very important as an antioxidant for cellular health, and helps to support the horse’s immune, nervous, and reproductive systems and aid in recovery after performance. Too little can lead to muscle weakness and trembling, and muscle atrophy (the loss of muscle.) Luckily for us, horses tolerate high amounts of Vitamin E quite well…but check with your veterinarian about how much is too much. Horses differ in their ability to utilize the Vitamin E, so the only way to be sure of your horse’s level is to ask your veterinarian to do a blood test. I know that many of you supplement with Vitamin E and selenium. Having blood work done will help you learn if you are feeding too much (and wasting your money) or not feeding enough. Interestingly, it’s now thought that Vitamin E may play a role in PPID (pituitary pars intermedia dysfunction, or Cushing’s). Let me be clear about this- Vitamin E WILL NOT prevent PPID, as there is still a genetic component, but the correct levels of Vitamin E may help your horse stay healthier longer.

Vitamin K is necessary for blood-clotting. The horse produces this vitamin in his hindgut. It can also be found in his forage. It’s rare for a horse to have a deficiency of Vitamin K, but it can happen if he has an infection in his hind-gut that disrupts the microbes that produce the vitamin. There are some plants that will cause low levels of Vitamin K if the horse eats them- one to watch for in our area is sweet clover (THIS IS NOT THE LOW-GROWING CLOVER THAT YOU SEE IN LAWNS OR PASTURES- it is a tall, spiky plant.) Low levels of Vitamin K lead to pale gums, irregular heartbeat, and internal bleeding. Because the horse produces this himself, there isn’t much information available on the effects of too much- presumably he is producing what he needs. Of course, this may prove to be different in the future as more research is conducted.

Vitamin B is water soluble and is produced in part by bacteria in the horse’s GI tract. This is not enough to meet his needs though, so he also consumes it in the form of fresh and dried greens and grains with husks. If he is eating a high-quality forage, deficiency is unlikely. There are some toxic plants though that can restrict his ability to absorb this, such as the bracken fern. A horse that is deficient will show signs of lethargy and loss of appetite and nervousness. Signs that your horse is getting too much include excitability and difficulty breathing, and in an extreme case, convulsions. Like Vitamin A, an excess of Vitamin B is usually because of the horse getting too much in supplements- in this case, injections.

Vitamin C is interesting because the horse manufactures it from glucose (remember glucose, a simple sugar?) Because he makes his own, deficiency is rare. Quite frankly, there aren’t a lot of published studies on Vitamin C in the horse’s diet, although it’s thought that in some cases a horse may benefit from supplemental Vitamin C. If you have concerns about your horse’s need, consult your veterinarian.

Okay, that wasn’t too hard, was it? Buckle up, things are going to get confusing. Now we’re going to talk about how to determine the amount that your horse is getting in his feed. We might even have to do some math.

When you look at your feed tag, the amounts of some vitamins are listed in IU/lb (International Units per pound) and others are listed as mg/lb (milligrams per pound.) That’s right. Not only are the units of measure not using the same terms, but some have the audacity to be mixed metric and imperial! How are we supposed to figure that out? Looks like math is in our future.

First, remember that these amounts are not the recommendations for how much your horse should be eating in a day. They are measurements of the amount of vitamins in that bag of feed. (Sigh…here comes the math.) I’m going to use a vitamin/mineral supplement as an example. This bag contains a minimum of 40,000 IU/lb of Vitamin A. (Bags of feed will contain less than this.) If you are following the recommended feeding rate for this supplement and he is eating a pound a day, then he is getting 40,000 IUs per day from this supplement alone. (Remember, he is also getting Vitamin A from his pasture, hay, and other feeds that you may be giving him, so he is getting more than 40,000 IUs in his total diet.) If you are giving him a feed that has 3000 IU/lb and he is eating five pounds per day, then he is getting 15,000 IUs per day from just the feed. (And that, my friends, is why I’m always after you to feed by the pound, not the scoop. There is no “IUs/scoop measurement.)

Just what is an IU, anyway? I’m not really sure, I just know that it is a tiny amount. But someone went through a lot of research and time and thought to set those up. Basically it’s a way to compare the effectiveness of different vitamins across the board, so that the rest of us don’t have to fancy calculations. Vitamins A, D, and E are expressed as IU/lb.

Vitamins B and C, if they are listed at all, are on your feed tag in mg/lb. (Seriously?? What’s with mixing metric and imperial?) Luckily, we don’t have to break that down, because it’s telling you how many milligrams of each vitamin are in a pound of the feed or supplement, and if you look at a horse’s requirements per day, it’s listed as milligrams. Of course, if you want to convert milligrams to ounces, go right ahead!

In our example of a vitamin/mineral supplement, let’s look at Vitamin B. Oh wait…there is no Vitamin B listed. That’s because Vitamin B has several different forms. Thiamine is B1, Riboflavin is B2, Biotin is B7, and there are more. The math is still the same though: mg/lb will tell you how many milligrams are in a pound of the supplement. If you are feeding one pound and the bag tag claims that there are 3.8 mg/lb in the product, than you are feeding 3.8 mgs.

Now take a look at your bag tag, or the information on the back of your bag of feed. Do you see Vitamin K and Vitamin C listed? I’ll bet that you don’t. This is because the horse can manufacture Vitamins K and C, as we discussed above. There may be some present in the feed but not listed on the tag because the amounts aren’t guaranteed.

If you want to figure the total amount of a vitamin that your horse is getting in his diet, then you will need to consider all the sources. Let’s use Vitamin E as an example, because it is one that many people supplement. As we said earlier, horses vary in their ability to use Vitamin E. You could feed the same diet to three horses in your barn, all of whom are similar in age, breed, use, etc., and one could be deficient, one could be eating too much, and the third, like Goldilocks, could be just right.

You can determine the amount of Vitamin E in your feed and supplements by using the info on the tag or label. You likely won’t find anything regarding Vitamin E on your hay analysis. Remember, Vitamin E disintegrates quickly after hay is cut. And you can’t determine the amount of Vitamin E in pasture without having your grass tested, and that can be hard to do. If you have concerns about your horse’s Vitamin E consumption, talk with your veterinarian.

Phew! That’s a lot of info. My hope is that after reading this, you will have an understanding of why vitamins are important to your horse, where they are found in his diet, and how to determine what your horse is consuming. Next month…minerals!