Sport horses might need increased amounts of protein as their workloads increase. | Getty imagesQ. I have an upper-level dressage horse that is in a rigorous training program six days a week. He is currently in good condition with a body condition score (BCS) of 5. Because he is working hard, Im concerned about his protein intake. What are the best sources of high-quality protein for me to look for or add to his feed?A. Protein is an important part of your horses diet and is one of the six required nutrient classes for horses. Taking a keen interest in your horses protein intake is important because when a horses workload increases, his or her protein requirement increases as well.Proteins are a major component of body tissues and play key roles in enzymes, hormones, and antibodies, so consuming a quality protein source is imperative to working horses health. Protein is also necessary for muscle development and repair, which is necessary for horses in work.Amino Acids in Equine DietsProtein molecules are composed of amino acids. There are 21 main amino acids, 10 of which are essential, meaning the horse cannot synthesize them and we must provide them in the diet. The National Research Councils (NRC) Nutrient Requirements of Horses, published in 2007, provides a recommendation for horses crude protein intake as well as lysine intake. Lysine is the first-limiting amino acid for horses, meaning it is the first essential amino acid in which they become deficient. Although equine researchers do not yet know how much of each essential amino acid horses need, we know that lysine, threonine, and methionine are the first three limiting.High-quality protein is readily digestible for the horse in the small intestine if the protein source is providing the essential amino acids in correct amounts. A lower-quality protein source might not provide the key amino acids or be as digestible.Evaluating Protein Content in Your Horses DietBefore you focus on the protein in your supplemental products, you should first look at the hay, which almost always makes up most of the horses diet. If you are concerned about your horses protein intake, first order a hay analysis. Simply adding more protein to your horses diet without analyzing your hay first can eventually have negative effects on your horses health.Excess and Deficiency in Equine DietsIn equine diets too much or too little protein can cause health issues. Performance horses maintained on high-quality hay with supplemental feeds are unlikely to have protein deficiencies.Excess dietary protein is not typically an issue for healthy horses because they can break it down and excrete the excess, but it can put unnecessary strain on the kidneys and liver. Horses do not store protein for later use the way they do carbohydrates and fats.When horses consume excess protein for a prolonged period, it can increase the horses heat production and urine output and create a significant ammonia smell in the stall that negatively affects the respiratory tract. Additionally, protein is a costly feed ingredient so providing it in excess makes the ration unnecessarily expensive.Choosing A Quality Protein Source for Your HorseWhen evaluating protein in the diet, look at the crude protein your hay and feed supply and evaluate the quality of the protein source. Hay provides protein to the horse, and legumes such as alfalfa serve as high-quality protein sources. Other high-quality protein sources include soybean meal, canola meal, flax, whey, sunflower meal, and a variety of legumes. Equine nutritionists typically regard cereal grains (i.e. oats or corn) as lower-quality protein sources.When reading the label of the feed you have chosen for your horse, instead of just looking at the crude protein percentage, you should also take a close look at the ingredient list. Take note of the protein sources and be conscious of where they lie on the list. Ideally, the higher-quality sources should be at the top of the ingredient list, meaning they make up most of the products protein content. If the higher-quality sources are toward the end of the ingredient list, it indicates they make up a smaller portion of the feeds protein.Take-Home MessageThe crucial first step in planning an optimal diet for your horse is to pursue a hay analysis, which will help you understand how much protein your forage is providing. This information will help you be confident you are meeting your horses crude protein requirement. From there, you can critically evaluate your horses feed to ensure there are high-quality protein sources in the ingredient list such as alfalfa, soy, canola, whey, legumes, or even sunflower meal. Choosing a commercial feed that mainly includes high-quality protein sources is a good way to ensure the product is supplying highly-digestible protein to your horse.