This is the first article in the “Fix It With Feed” series. Check back every Wednesday, starting Jan. 26 for more articles on nutrition and how it affects performance.

Trying to decide which feed to give your horse can feel like clothes shopping—you squint to read the numbers on the tag, but you’re never quite sure if it’s a perfect fit.

But while size is the only number you have to decipher on your clothes, the tags on horse feed have a dizzying array of figures. It can seem like code-breaking as you try to ascertain which grain might be the best for your horse.

The first number on every feed tag is the protein percentage, yet feeds come with a wide range of protein percentages, anywhere from 8 percent to 16 percent. Then there are all the various stories about protein. Is more better? Will too much hurt your horse? Does it make a horse hot? Help a horse put on muscle? What does your horse need?

What Does Protein Do?

In order to know what percentage of protein best suits your horse, it’s important to understand the vital role protein plays in the horse’s diet. Protein is an integral part of every tissue and organ in the horse’s body.

“Most people are afraid of protein,” said Dr. Juliet Getty of Getty Equine Nutrition LLC in Bayfield, Colo. “But the horse has to have those amino acids in his system to replace tissues like skin, hair and hooves. It keeps his blood and systems healthy, and it builds muscle.”

A protein is a complex molecule composed of a wide array of building blocks or amino acids. All 22 amino acids are required to build body proteins, but some of these building blocks can be converted from one to another, while others must be provided in the diet. These are the essential amino acids. The percentage values of three of the most important of these—lysine, methionine and threonine—are commonly listed on feed tags. (See sidebar for more information about essential amino acids.)

How much tissue rebuilding a horse’s body does dictates his protein needs. A horse who lives in a pasture and goes for pleasure rides a few days a week doesn’t stress his muscles and tissues enough to require significant rebuilding. Therefore, he has a lower protein requirement.

A horse competing at a high level, with repeated stress to his body tissues, will need more protein in order to maintain and rebuild those tissues, especially muscle. A growing young horse has higher protein needs because he’s continually adding tissue and building muscle. Likewise, a broodmare—in the gestational and lactating stages—will need additional protein to support the demand the foal places on her body.

It’s important to note that protein is an inefficient energy source for the horse’s body. A horse’s calorie requirements might increase dramatically with intense work, but his protein requirements will stay relatively stable. Ideally, the horse’s body uses protein purely to maintain and rebuild body tissues, while using carbohydrates and fat as caloric energy sources.

Not many feed companies print the energy content, or megacalorie per kilogram, on the feed tag, but this is important information to consider when deciding a horse’s diet. Feeding more protein doesn’t add energy in a productive way; feeding more calories in the form of carbohydrates or fat does.

Where Does Protein Come From?

It’s important to consider the protein percentage in your horse’s forage as well as what’s in his grain ration. “The protein requirement just to maintain a horse is around 8 to 10 percent protein, with grain, hay and forage included, to grow hair and hooves and maintain muscle tissue and bone,” said Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Fresh pasture is the best forage to put protein in your horse’s diet, as spring grass contains 23-28 percent protein, and autumn grass has 14-18 percent protein. Grass hay ranges from 6 to 10 percent protein, while legume hay, such as alfalfa, has twice as much protein as grass hay. Fresh cut alfalfa can contain as much as 20 percent protein. It’s a good idea to have the protein percentage of your hay and pasture grass tested, so you’re aware of it.

Figuring out what protein percentage grain you should feed requires a little bit of math to determine the total protein percentage of your horse’s diet. Let’s say your horse eats 30 pounds of a grass hay with 10 percent protein daily. That’s 3 pounds of protein from forage. Then, he eats 4 pounds a day of a 12 percent protein grain. That’s 0.48 pounds of protein. Your horse’s total protein intake is 3.48 pounds of a 34-pound total diet, which calculates out to a 10.24-percent protein intake.

For a performance horse “the protein concentration of your horse’s total ration should fall within 10-12 percent,” said Crandell. “An appropriate concentrate should be chosen based on the protein content of your forage and how much concentrate your horse requires to maintain his optimal body condition.”

If your horse is an easy keeper and maintains good weight with minimal grain, a ration balancer might help provide the essential protein and nutrients without adding too many calories. Don’t worry that ration balancers typically have a higher protein percentage listed on the tag.

“A ration balancer is a class of feed that is formulated to provide good quality protein and essential amino acids along with an optimal balance of vitamins and minerals. Ration balancers are a low intake feed, so they can be fed at 1 or 2 pounds a day,” said Crandell.

Feeding 2 pounds a day of a 25-percent protein ration balancer adds just .5 pounds of protein to your horse’s total diet. “It’s not an overdose of protein if fed at the recommended feeding rate,” Crandell continued.

You can also tell a lot about the protein in your horse’s feed by reading the ingredients label. Protein can come from many sources, including animals, plants, milk or fishmeal. Most horses find feeds with plant-based protein more palatable and easier to digest. Feeds with animal protein sources or fishmeal sources may have an odor or different taste. Animal sources, however, often have the best amino acid profile and highest levels of lysine. Milk protein is often used for foal feeds.

“When you read crude protein on the feed label, it tells you nothing of the quality,” said Getty. “You want a protein that has all the essential amino acids in the right proportion. Higher quality protein feeds will have a mixture of ingredients such as alfalfa meal or soybean meal.”

Keep in mind, though, that feeding a diet high in protein—even if a supplement or feed claims to help build muscle or topline—will need to be i used in conjunction with exercise for muscle development. A body builder who drinks protein shakes all day and does no exercise is just overweight and not muscular—anything that offers to be an easy quick fix is often to good to be true

Does Protein Make A Horse Hot?

“If you give a horse excess energy in any form, whether it’s carbohydrates or protein, it can make them ‘hot,’ or excitable, but protein is not the usual culprit,” said Crandell.

It’s important to distinguish between protein and energy. Protein’s main job in the horse’s body is to rebuild body tissues such as muscle, not to serve as an energy source. The horse’s body converts protein to calories for energy only when it is fed in excess, or if there are insufficient calories in the diet.

“The reaction of a horse when you give him more grain and he gets hotter, more active and spooky, is mostly from just having more energy, more calories. That energy comes from the carbohydrates in the feed more so than the protein,” Crandell said. “People sometimes worry that they can’t feed 12 percent feed ‘because it makes my horse hot.’ Well, if you’re only feeding 4 pounds of 12 percent, there’s not that much difference in the amount of protein in that ration versus 4 pounds of 10 percent protein feed. It’s minimal.”

If your horse is reacting to a new feed by becoming excitable and tense, or hot, he’s probably reacting to a higher energy content, not a higher protein level. Carbohydrates—sugars and starches—are converted to glucose in the digestion process, which is then absorbed into the blood. The more sugars and starches ingested, the higher the blood glucose level, or blood sugar level. Studies have shown a link between blood sugar levels and mood swings and hyperactivity in humans.

More Is Not Better

Conventional wisdom once held that excessive protein in a horse’s diet would lead to kidney damage, but that’s not so. “It’s an old wives tale about protein harming the kidneys,” Crandell said. “If you feed too much protein, the body can break down excess protein and use it as a calorie source, but it’s not a very efficient way to make calories.”

The body’s process for breaking down protein into calories results in nitrogen as a byproduct, which gets filtered out of the body by the kidneys. A horse that is converting excess protein to calories will drink more water to aid that filtering, and its urine may have a strong ammonia smell, as the nitrogen is excreted as urea.

Although healthy horses can process excess protein, there’s no benefit to overloading. Protein isn’t an efficient energy source—more of its energy is lost during metabolism than with carbohydrates. And the process of breaking down protein creates more heat than breaking down carbohydrates or fat, which can affect a horse’s performance ability in hot weather.

On the other hand, protein deficiency can cause serious issues. A horse that isn’t getting enough calories for energy will start using protein for energy rather than muscle building. Horses with insufficient protein will have poor muscle development and tone, coat and hooves in poor condition, and lack energy and ability to concentrate.

Protein deficiency can also be a result of a sickness. “With certain diseases, the horse goes into high gear—it metabolizes more and breaks down proteins faster. They lose muscle tissue, because that’s where the body draws more protein from,” Crandell said.

Essential Amino Acids 101

Every amino acid is needed to build each body protein. Essential amino acids must be provided in your horse’s diet—they cannot be converted from other amino acids in the body. The balance of essential amino acids is important because any excesses will get burned for energy, and a deficiency means the body can’t build protein. The essential amino acids are as follows:

Lysine

• The “first limiting” EAA—If the horse doesn’t get enough lysine, he won’t be able to use any of the others, but a normal equine diet provides enough
• Feeds should contain a minimum of 0.65 percent lysine (dry matter)
• Growing foals require more for muscle development and bone growth
• Stimulates gastric juices

Methionine

• Also a “limiting” EAA
• Hair and coat growth
• Prevents deposits and adhesions of fat in liver
• Selenium absorption
• Antioxidant
• Anti-arthritic

Arginine

• Releases insulin and growth hormone
• Nutritional aid in cancer therapy, fights tumor growth
• Boosts T-cell production

Histidine

• Maintains plasma, hematocrit and serum albumin
• Releases histamine
• Controls pain
• Anti-arthritic
• Stimulates stomach acid secretion, improves appetite

Phenylalanine

• Produces epinephrine and norepinephrine
• Antidepressant

Threonine

• Enhances growth and food efficiency
• Produces adrenaline
• Precursor to thyroid hormones

Tryptophan

• Component of serotonin
• Mood stabilizer
• Precursor to niacin
• May aid in blood clotting

Valine

• Regulates protein turnover and energy metabolism with leucine and isoleucine
• Vital for muscle coordination

Leucine

• Keeps muscle protein from degrading

Isoleucine

• Forms hemoglobin
• Fights nervous system degeneration

If you enjoyed this article and would like to read more like it, consider subscribing to The Chronicle Of The Horse. “You Don’t Need A Ph.D. To Puzzle Out Protein” ran in the Jan. 17 issue. Check out the table of contents to see what great stories are in the magazine this week.