SO YOU THINK YOU KNOW PROTEIN

This month we’ll look at protein in the horse’s diet. This article isn’t meant to tell you how much protein your horse should have- that is a conversation to have with your veterinarian, and your horse’s requirements will depend on his age, job, and activity level. Each horse is an individual and should be fed as such. We’ll talk here about what protein does, types of protein, and how to determine how much your horse is getting in his diet.

Before we go further, let’s get a couple of misconceptions out of the way. First, protein does not make your horse hot. Excess energy, generally in the form of carbs, is what leads to those exuberant moments. Remember too that some horses just are hot: that is their nature. Eating enough protein helps them to be fit and feel good but in and of itself it is not a cause of hot behavior. A second misunderstanding is that exercise builds muscle and that’s not true either. Protein builds muscle. Exercise conditions it. More on this later.

Protein is so important that we could go on for pages and pages…but we won’t. You should know though how necessary it is to the equine body. The horse needs to eat protein daily because it affects so many body functions. Here’s the short version: it provides structure in the forms of bone, muscle, cartilage, skin, and hooves. It is responsible for growth and maintenance. It drives biochemical reactions such as digestion and blood clotting. It maintains the pH of body fluids and helps balance the fluids in the body (think swelling and inflammation.) It bolsters the immune system and helps to store and transport nutrients across membranes and in the blood. Protein provides energy and even affects saddle fit.

Let’s address the protein and energy question here. I wrote earlier that protein does not make your horse hot, and now I’m telling you that it provides energy. Protein can be a source of energy, but it is metabolically expensive. It is such a valuable component that the body prefers to use it for other functions. Energy also comes from carbohydrates and fats, both of which break down easily. Carbs and fats are easy to store, and well-fed horses have an abundant supply just waiting to be tapped. If your horse couldn’t eat, he would eventually run out of his stored fat and carbs and his body would then start to use protein as an energy source. It’s hard work for the body to break down protein for that use however, and it has the added burden of generating excess nitrogen which must be excreted. Here is another view: gram for gram, protein and carbs have the same number of calories (with fat having twice as much) but it’s easier to extract that energy from the carbs than from the protein. It is much more efficient to use protein for the other systems in the horse’s body. Think of it this way: yes, you can use your jack knife to open a can, but isn’t it easier to use a can opener? The jack knife has other uses for which it is better suited. Same with protein. Yes, it can be an energy source for your horse, but it’s easier for his body to use carbs and fats. Protein’s real role is for other functions in the body.

As stated earlier, exercise does not build muscle. Protein builds muscle. You can do all the exercises you wish but if there isn’t sufficient protein in the diet, muscling won’t happen. When a horse isn’t getting enough quality protein, you may notice that his topline drops and your saddle fit changes. That’s right- your saddle fit problem may be one of diet, not exercise. This is even more noticeable as horses age. We know that older horses don’t utilize nutrients as efficiently and as effectively as do younger horses, and this is why senior feeds tend to be higher in protein.

The horse’s body contains thousands of different proteins. Every cell in his body contains some type of protein. Does it surprise you to learn that? Protein is not just “one size fits all.” The protein that produces a hard hoof is not the same as that which transports nutrients in the blood, and both of those are different than the one that builds muscle. In order for all this to happen, proteins are constantly being broken down and synthesized by the horse’s body. This is why quality protein is such an important part of your horse’s diet.

Hopefully by this point you are realizing that protein isn’t really an ingredient- it is a legion of multi-faceted, multi-use units. Amino acids are the building blocks of those units. We won’t go into detail, but there are a few important points you should know. First, amino acids are categorized as either nonessential or essential. Now that does not mean that the horse needs some but not others…not even close! Nonessential means that the horse can synthesize the amino acids in his body. Essential means that he cannot synthesize them or cannot synthesize enough to fuel his needs. There are ten essential amino acids (EAAs). Of these, most people have heard of lysine, methionine, and threonine, because they are limiting essential amino acids. This means that if there aren’t enough of these, the other proteins can’t be synthesized. An example: if you are building an electric fence for your pasture and you run out of insulators, it doesn’t matter how much wire or how many posts you have. Without more insulators, your project won’t get done. Those insulators are like limiting essential amino acids.

Current research indicates that lysine is the most restrictive limiting EAA. If you are feeding a quality feed, it hopefully has lysine and maybe methionine and threonine listed on the guaranteed analysis. If you don’t see these listed on the bag tag, this doesn’t mean that your feed doesn’t contain them, but it does mean that the amount isn’t guaranteed so you don’t really know how much your horse is getting. They are also available as supplements but consult with your veterinarian before you start adding additional EAAs to your horse’s diet. If your horse is on a mainly forage diet, adding a ration balancer (fed by weight according to the bag) will provide his EAA needs.

Essential amino acids are in many of the ingredients in horse feeds, such as soybean meal, oats, and legumes. And here is where things get tricky: these ingredients don’t all provide the same quality of protein. Some ingredients are a better source of protein than others. If you read the “bag tag” article from a couple months ago, then you’ll recall our discussion about least cost feeds, mid-range/fixed formula feeds, and high-end/fixed nutrition feeds. The source and quality of the protein is one of driving factors in determining the category that the feed is in. In any feed, whether it’s for horses, dogs, cats, chickens, wild birds, etc. the protein tends to be the most expensive ingredient.

Take a look at your feed bag. Can you determine the protein source? It’s usually one of the first ingredients listed. If you are looking at a ration balancer or a high-end/fixed nutrition feed, I’ll bet that it’s soybean meal. Soybeans have the amino acid profile that most closely resembles what horses need. If the first ingredient is something like wheat middlings, with soybean by-products a bit further down the list, yours is probably a mid-range/fixed formula feed. And if the first ingredient is something like “processed grain by-products” or “grain products” or “roughage products”, then that’s a low-end/least cost feed. Least cost feeds use whatever is the cheapest at the time of manufacture. It could be cottonseed meal, corn, oats…you don’t know. They all have amounts of lysine that is significantly lower than that of soybean meal. And remember, lysine is a limiting EAA. If you don’t have enough of it, the other amino acids can’t do their jobs. (See chart, courtesy of Iowa State University Extension and Outreach)

	CRUDE PROTEIN, %	LYSINE mg/g CP ( milligrams of lysine
Corn	9.1	29 per gram of feed or
Whole Oats	13.6	42 forage, measured as
Flax Seed Meal	32.6	37 crude protein)
Soybean Meal	53.8	63
Grass Hay, mid-maturity	13.3	35
Legume Hay, mid-maturity	20.8	51
Grass Pasture	26.5	35
Alfalfa pasture	26.5	52

Protein is also available in your horse’s pasture in the form or grass. It tends to be a low amount though and is hard to measure as the nutrient content of grass changes during the course of the day. It can be found in your hay too. If you have your hay analyzed, you’ll be able to tell how much protein it contains. We’ll talk about the math of that near the end of this article.

Horse feed and forages measure crude protein, which has a long definition that basically says it’s determined by how much nitrogen a horse eats and how much they eliminate in urine and manure. (Yeah…that’s someone’s job!) It’s the best guess of the feed’s protein content. It would be better to describe the digestible protein of a feed, but the data regarding that value for horses doesn’t generally exist.

If you have done any research into human nutrition, you will know that protein is also available in animal products, such as meat and fish. We see them in the forms of lamb meal, chicken by-products, and fish meal in our dogs’ and cats’ food. Animal proteins not recommended for herbivores such as horses though. This is because they have limited digestibility and may contain toxins that affect the horse’s gastro-intestinal tract. Most horses don’t like the taste anyway, aside from my Mini that snacks on cat food whenever he is allowed to free-range in the barn! Animal proteins also tend to have a higher level of nitrogen that needs to be eliminated from the body.

Why does the source and quality of protein matter? Because, after water, protein is critically important to ALL of your horse’s functions. Do you have a performance horse? Better quality protein helps him build muscle and recover from exertion quicker. The more work he does, the more protein his body needs. Do you breed? Better quality protein, and more of it, helps the dam as she goes through gestation and nursing and gives the foal his best possible start. In fact, growing horses have a higher lysine requirement than mature horses. Do you trail ride? Better quality protein helps the horse to maintain muscle condition and generates better hoof quality. Do you have a pasture pet? He still needs good quality protein just for everyday functions like digestion, blood circulation, and maintenance.

When you look at a bag of feed, the first number in the list of nutrients indicates protein. This is not telling you how much protein your horse should have in his diet; it is telling you how much protein is in the bag of feed. If you are buying a 50-lb bag of feed that lists protein as 10%, that means that 10% of the bag, or five pounds, consists of protein. To determine how much your horse is getting from his feed, you’ll need to weigh how much you give him in a day. (If you weigh one meal, remember to multiply that weight by the number of meals you give him.) If you feed five pounds of feed per day and it’s 10% protein feed, then he’s getting 0.5 pounds (5 lbs x .10.) Remember, we’re not talking about how much protein he should be eating, we’re just using these numbers to determine how much he is actually consuming.

Now let’s look at a ration balancer, which can be as much as 30% protein. If he is eating one pound per day, then he is getting 0.3 pounds. Can you see why doing the math is so important here? You may have thought that a 30% ration balancer has too much protein, but if you are feeding it as specified on the bag and you are feeding by weight (and not by the scoop), then your horse isn’t really getting an excessive amount. Remember, ration balancers are supplements, not feed.

Of course, your horse is getting protein from his pasture and his hay or other forages too. If you want to figure how much protein he is getting in his total diet, you have to do the math for those as well. As we discussed earlier, it can be hard to determine the protein level in his pasture. The time of year, the weather conditions, and the types of grass in the pasture all affect that number. Most of us don’t have the equipment to measure the protein level in the grass, so we’re going to ignore it here. You can figure how much he is getting in his hay though by having a hay analysis. (In case you’ve forgotten how this is done, take handfuls of hay from several bales, put them in a one-gallon sized resealable bag, and take it to your local feed store.) Once you get your hay results, the math is similar to what we did above. Let’s say your hay analysis reports 7% crude protein. If he is eating 20 pounds of hay per day, then he is getting 1.4 pounds of protein from his hay (20 lbs X 0.07.) You can follow the same steps to determine the amount of lysine he is eating if your feed tag lists it.

Now here’s the last part: to figure out how much TOTAL protein he’s eating in a day, you have to add up the amount of protein of all that he eats: feed, supplement, and forages (excluding grass because we can’t do that at home.) That will give you an answer in pounds. If you want to figure the percentage of his diet that is protein, we have a couple more steps to do. You’ll need the total weight of the protein that he is eating (we’ve just done all this math in the paragraphs above) and you’ll need the total weight of everything that he is eating. Divide the pounds of protein by the pounds of feed. If he is getting 0.5 pounds of protein in the five pounds of feed and 1.4 pounds in the 20 pounds of hay, then he’s getting 1.9 pounds of protein/25 pounds or 0.076. That means that protein is almost 8% of his diet, and that’s on the low side if he’s doing any work.

So, what does that mean? Before you get panicky, please know that protein deficiency is not that common in horses. If you are feeding to the specifications on the feed bag, your horse is likely covered. If, however, you are not feeding enough protein to supply his body’s needs, the effects of a low protein diet will show up in poor muscling, weak topline, hoof quality, hair, and general un-thriftiness. Those are what you will see externally- there is more going on inside. Luckily, it’s easy to fix increasing his feed, adding a ration balancer, or providing a higher protein feed.

What if your horse is getting too much protein? This generally isn’t a problem either, as the horse is very efficient at excreting it through urine and manure. In fact, if the ammonia fumes in his stall can knock you down in the morning, it is likely because he is eating more protein than he needs, and his body is ridding itself of the excess. This is a sign that you should re-evaluate his feed. Your horse’s sense of smell is much greater than yours. If you are overwhelmed by the odor, consider what he has been breathing all night.

There are scenarios where excess protein can be of concern though. Horses that are consuming excess protein also tend to drink more as their body needs water to break down the protein and excrete it through urine. If your horse doesn’t have access to enough water, he can become dehydrated. Excessive peeing can also lead to the loss of electrolytes, which can be a very serious health concern in performance horses. And if your horse’s kidneys aren’t healthy, excessive protein can be disastrous. Note that alfalfa hay can have high levels of protein. If your horse eats alfalfa hay, provide extra water.

Let’s finish up with a couple crucial points. Last month we looked at the importance of water, and this month we’ve looked at protein. Both are critical nutrients to the horse; both need to be part of his diet every day. He has to have access to clean, fresh water in order for all his body functions to work, and he has to have quality protein to support his body and allow the water to do its job. As responsible horse owners, it’s our job provide him with both.