Feeding horses can be a constant balancing act since nutrient requirements change depending on the horse’s age, level of exercise, metabolism, as well as several other factors. Chances are no two horses at your barn will be fed exactly the same. But having a good understanding of the three main energy sources in horse diets--protein, carbohydrates, and fat--will help you to tailor your individual feeding programs accordingly.
Understanding horse nutrient requirements by work level
When it comes to exercise, the National Research Council (NRC) places horses into four main categories: light, moderate, heavy, and very heavy work. Knowing which category your horse falls under is important for determining his individual nutrient requirements.
The exercise categories for horses are defined as:
Light exercise: 1-3 hours of exercise per week (40% walk, 50% trot, 10% canter). Examples: recreational riding, starting a training program, some show horses.
Moderate exercise: 3–5 hours per week (30% walk, 55% trot, 10% canter, 5% low jumping, cutting, etc.). Examples: school horses, recreational riding, show horses, polo, ranch work.
Heavy exercise: 4–5 hours per week (20% walk, 50% trot, 15% canter, 15% gallop, jumping, etc.). Examples: ranch work, polo, frequently showing horses, low-level eventing, race training.
Very heavy exercise: variable hours per week. Examples: racing, endurance, elite three-day event horses.
How much protein do horses need?
Protein is often the first nutrient horse owners think about when feeding, though it isn’t the top energy source for horses. However, protein, which consists of individual amino acids, is needed to maintain and produce muscle, enzymes, and hormones, as well as help with many different body processes.
The horse’s body can produce some amino acids on its own, but others must be supplied by the diet. These are known as essential amino acids, and lysine is the one most owners may be most familiar with, as it is needed in higher amounts.
With protein, quality is more important than quantity, and this has to do with the amount of amino acids a feed contains. For example, soybean meal contains more lysine than cottonseed meal and would be considered a higher quality protein.
Dr. Amanda Bradbery, FullBucket’s senior equine nutritionist explains, “Protein requirements increase only minimally in mature horses under exercise and should not be used as a primary source of energy. Protein concentration in commercial grain increases in an effort to maintain the essential nutrient:calorie ratio. Protein concentrations, therefore, must increase proportional to increasing energy demands.”
The National Research Council gives the following protein recommendations for the average-sized horse around 1,100 pounds:
- For mature horses, those in early pregnancy, or in light work: 1.4 pounds per day (which can often be provided by grazing or eating grass hay at 22 pounds per day);
- For mature horses in moderate to heavy work: 2 to 2.15 pounds per day;
- For broodmares in late pregnancy: 3.4 pounds per day;
- For lactating mares (first 3 months after birth): 2.75 pounds per day;
- For weanlings weighing 550 pounds: 1.6 pounds per day; and
- For yearlings weighing 850 pounds: 1.75 pounds per day.
Older horses (20+) may have increased protein requirements as well, but assessing renal function is important before feeding them a high protein feed.
To add more protein into a horse’s diet, feed the same amount of forage (22 lbs in this case) and add in a fortified feed or specific high protein ingredients. Here are some examples:
- Dried split peas (23-25% protein)
- Alfalfa–hay, cubes, or pellets (19-23%)
- Flaxseed meal (31-35%)
- Hemp seeds (33%)
- Chia seed (19-23%)
- Soybean meal (44-52%)
- Sunflower meal (26-30%)
- Wheat bran (15-20%)
Signs of protein deficiency in horses include a rough or coarse hair coat, weight loss, reduced growth in young horses, or reduced performance in adult horses. On the flip side, excess protein in the diet can lead to increased water intake and urination as well as increased sweat losses which can result in dehydration and electrolyte imbalances, so feeding the right amount of protein for each individual horse is important.
According to Dr. Bradbery it is important to remember that “Protein deficiency is uncommon in most equine diets, however, extreme protein excess is both metabolically and economically costly. Protein is an expensive ingredient and its conversion to energy is metabolically inefficient making it an important economic consideration when fed in excess.”
Carbohydrate requirements (or starch for horses)
Carbohydrates, aka sugars and starches, are the primary energy source for horses, and they can be classified into two main categories:
- Nonstructural, which are those occurring as simple sugars (including glucose, fructose, lactose, sucrose, and starch) that can be broken down by enzymes in the horse’s small intestine and used for immediate energy needs.
- Structural, which come from the fibrous portion of plants and must be fermented by bacteria in the gut and converted into volatile fatty acids before they can be utilized as energy.
Nonstructural carbohydrates are found in nearly every type of concentrated feed but are highest in those containing corn, barley, or oats. Though working horses often require more carbohydrates than non-working horses, high amounts of this nutrient can also spell disaster, especially for horses with insulin resistance or equine metabolic syndrome.
Ingesting high amounts of high carbohydrate feeds at once can also induce colic or laminitis in any horse, so they should always be fed in moderation, and caution should also be used when grazing horses on lush pasture.
Hay or grass provides the greatest percentage of structural carbohydrates in a horse’s diet, but grains with hulls can contribute to the total amount. Again, mature, idle horses or those in light work can get most of their carbohydrate requirements from pasture or grass hay, alone.
That being said, it is important to consider your horse’s work level and work with an equine nutritionist for guidance.
“In recent years, starch has become a feared ingredient in the equine industry. When in excess, it can become a concern with regards to metabolic dysfunctions; however, it is an important and often necessary ingredient in performance horse diets. Any form of exercise with long duration or high intensity will require glucose; therefore, starches and sugars in the diet are often necessary for performance horses,” Dr. Bradbery explains.
Fat requirements for horses
With twice as many calories as carbohydrates or protein, fat is a good energy source for horses and might be especially important for those in hard work or needing to gain weight.
Belonging to a group of compounds called lipids, dietary fats are usually triglycerides which contain three long-chain fatty acids and one glycerol group. Volatile fatty acids, on the other hand, are short-chain fatty acids produced by digesting structural carbohydrates from grass or hay or coming directly from dietary sources of fat. They can also provide energy for the horse.
Fat is needed to absorb the fat-soluble vitamins A, D, E, and K, and dietary fat also provides essential fatty acids like omegas 3 and 6, which the horse’s body cannot produce on its own. Because fat takes longer for a horse to digest, it releases a steady supply of energy over time.
As Dr. Bradbery notes, “Fats are a unique form of energy in that they are more calorie dense than carbohydrates, they have a low heat increment, and a glycogen sparing effect. Heat is a common byproduct of metabolism, but the metabolism of fat for energy results in less heat production than carbohydrates making it a great source of energy in hot/humid climates. The glycogen sparing effect allows the horse to use fats during normal aerobic exercise and conserve stores of glucose for anaerobic metabolism, which includes long duration workouts and events involving quick bursts of speed.”
Fat isn’t required by the horse in high amounts, but research suggests that horses can handle up to 20% fat in the total diet and high fat horse feeds, fat supplements for horses and oil for horses have steadily gained popularity, especially for animals with certain metabolic conditions.
However, as with any feed change, supplemental fat should be gradually introduced into the diet to avoid digestive upset. Horses do not have a gallbladder, so bile is secreted directly into the small intestine to help them digest fat. Some commonly fed fat sources include rice bran and vegetable or other types of safe oil for horses.
Protein, carbohydrates, and fat are the primary three ingredients in the horse’s diet, but in our next segment on nutrient requirements for horses, we’ll get into the really exciting stuff--the micronutrients that power many of the horse’s body systems, but which are needed in small amounts!