In the second installment of our three-part commercial feed tag series, we take a look at working horses and their energy needs.
It probably goes without saying, but performance horse feeds are designed to meet the nutrient requirements of athletic horses. The greatest increase in nutrient requirements (other than water!) these animals experience when they work or perform is energy, which is quantified in the diet as calories. Heavily exercising horses burn more calories than they might be able to consume with hay or pasture alone. Thus, manufacturers have designed commercial performance feeds to boost horses’ calorie intake, as well as to meet additional nutrient needs that increase with work.
In the figure below, you can see energy and protein requirements rising with increasing levels of work and how the horses’ elevated calorie needs are far greater than their elevated protein needs. While other nutrient requirements, such as those for calcium and phosphorus, also increase with work, calories should always be your biggest concern.
But despite the athletic horse’s need for calories, these nutrients are not listed on equine feed tags! The unit of measure of calories in equine feeds, expressed as Mcal, or megacalories per kilogram of feed, is called digestible energy (DE). Digestible energy refers to the amount of calories available to the horse after digestion, and this depends on how well a horse digests a type of feed and the calories that are in it.
Gross energy (GE)—or the potential energy of a feed’s energetic components, or substrates—also impacts the DE of a feed. Manufacturers determine this through bomb calorimetry—literally setting a substance on fire and measuring how much heat is released. In general, fats contain 9 Mcal/kg, sugar about 4 Mcal/kg, and protein about 5 Mcal/kg.
Different horse feeds contain different mixes of simple carbohydrates, fiber, protein, and fat. Combining the digestibility of different types of feed (for example, hay and grain) and the GE from feed’s different substrates gives us different amounts of DE for different feeds.
For example, horses can digest simple carbohydrates, such as starch or sugars, fairly well, while they have a more difficult time digesting complex carbohydrates, such as cellulose. (In fact, rather than being truly digested, this fiber is fermented by the microbes in the large intestine.) Thus, complex carbs provide the horse with less energy than do simple ones.
Calories are generated from the metabolism of energetic substrates. These include:
- Glucose, which is derived from starches and sugars found in many cereal grains;
- Volatile fatty acids, which are produced from fiber fermentation in the horse’s large intestine;
- Fatty acids, which are generated when a horse digests a fat source such as oil or a high-fat feed like rice bran; and
- Amino acids, which come from protein digestion.
Note, however, that for horses to use amino acids (protein) for energy, they must first metabolize them to remove their signature nitrogen unit, which the horse excretes in his urine. This makes protein a relatively inefficient calorie source.
Vegetable oil or other straight fat sources offer more digestible energy and yields more calories per unit weight (~9 Mcal/kg) than corn (about 3.6 Mcal/kg; high in starch) or grass hay (~2 Mcal/kg; high in fiber).
Therefore, while feed manufacturers aren’t required to list DE on feed tags, nutritionists can apply certain equations to estimate a feed’s DE, using the amount of fat, fiber, protein, ash (minerals), and simple carbohydrates.
Similarly, owners can look at a feed tag to see how much crude fat and crude fiber it contains, which will infer how much energy might be in it. In general, higher-fat feeds will offer ample calories, while higher-fiber feeds tend to be low in calories.
Calories can also come in the form of starch or sugar (e.g., nonsoluble carbohydrates, or NSCs), but manufacturers aren’t required to list these on a feed tag either. However, by looking at a feed tag you can estimate how much “nonfiber carbohydrate” is in the bag. If you imagine most grain mixes are about 10% water and maybe 6-7% ash, then what remains is protein, fat, fiber, and nonfiber carbohydrate.
For example, which feed would likely have the most calories?
- Feed X: 12% Crude Protein, 10% Crude Fat, 8% Crude Fiber
- Feed Y: 12% Crude Protein, 4% Crude Fat, 20% Crude Fiber
- Feed Z: 12% Crude Protein, 8% Crude Fat, 10% Crude Fiber
The answer would likely be X, as it has more fat (higher calories per unit weight) and lower fiber than Feed Z and likely higher starch and sugar content than Feed Y. So, how do you know if your horse is getting the energy he needs from these various feeds while he is at work? The easiest way is to determine his body condition score. Using the 1-9 Henneke scale (download a visual description of the scale at TheHorse.com/137703), you can determine how much stored energy (as fat) your horse has. Ideally, most working horses should be in the 4.5-5.5 body condition range, though this varies by sport. If your horse isn’t getting the calories he needs from his total diet (hay plus grain), then he will lose weight and it’ll be easy to see his ribs. Alternatively, if you feed too much, as he gains weight you will no longer be able to feel your horse’s ribs as you would be able to at 5. For this reason, the easiest nutrient for owners to monitor equine consumption of is dietary energy, with the exception of, perhaps, water.
Special Energy Considerations
Paying attention to your horses “spirit” level, or “oomph” as I call it (to avoid using the term “energy” again and not confuse it with calorie energy), can also help you select the correct performance feed for your horse. Note, however, that when a horse appears lazy, it is not always for lack of calories in his diet. Often he is lazy because he is overweight and carrying around added pounds that require more work effort. Losing weight would potentially give him more “oomph.” A horse’s spirit might also be a result of his breed and temperament. On the other hand, if a horse is highly spirited you might not want to decrease his grain intake but, rather, be smarter about how you feed him (e.g., offer smaller meals more frequently).
Another consideration for dietary energy source is how the horse actually metabolizes the substrate. Fat (and volatile fatty acids from fiber fermentation) is considered a “cool” energy source, while glucose (from starch and sugar) is considered a “hot” energy source. This has nothing to do with actual temperature; it involves behavior. Some horses are very sensitive behaviorally to increases in blood sugar concentrations, which can happen after a high-starch or sugar meal. Feeds containing a lot of oats or barley are quite high in starch and can result in higher blood glucose concentrations following consumption that might impact the horse’s behavior (similar to how a child might act after eating a chocolate bar). Therefore, an owner might prefer a feed that is higher in the “cool” calories, such as fat and fiber (beet pulp is one possible source), and lower in starch and sugar. They can call the feed company to determine the nonstructural carbohydrate content, or they can deduce it themselves by noting the fat, fiber, and protein content on the label.
High-NSC feeds can also disrupt glucose and insulin dynamics and might increase a horse’s risk of developing insulin resistance (a reduction in a horse’s sensitivity to insulin that makes it harder for the fat, muscle, and liver cells to transport the glucose out of the bloodstream and store it as glycogen, a fuel source). Certain horses, such as those with muscle disorders—examples include polysaccharide storage myopathy or recurrent exertional rhabdomyolysis—might also be sensitive to high amounts of starch and sugar in their diets. Owners of these horses might prefer to buy a feed that is higher in fat and fiber and lower in starch and sugar.
Some horses, however, do benefit from high-starch and sugar feeds. Horses that rely on muscle glycogen for bursts of energy, such as with racing or jumping, need a good glucose supply (from starch and sugar digestion and metabolism) to synthesize muscle glycogen. Go over the feed tag with your trainer and nutritionist to determine what ratios of fat, starch/sugar, and fiber your horse will perform best on.
Similarly, you can minimize any negative risks of feeding lots of grain through smart feeding techniques, such as increasing your horse’s number of daily meals, so each one is a little smaller (rather than offering one or two large meals per day).
Other Required Nutrients
So, we’ve got the energy part down. What else do equine athletes need in their diets? First, protein is listed on feed tags. Typically, it’s not difficult for horses—even athletes—to meet their protein requirements; because horses naturally eat more food to meet calorie needs when their workload increases, they generally also consume more protein.
For example: A horse in light work might eat 16.5 lbs of 8% protein hay (getting 600 grams of protein) and 4.5 lbs of a commercial feed with 12% protein (240 grams of protein). Therefore, he would be eating 840 grams, well over his 699 gram requirement, based on the National Research Council’s guidelines.
The same horse, if he went into heavier work, might eat more to meet calorie needs, such as 22 lbs of the same hay (800 grams of protein) and 8.8 lbs of the commercial feed, still at 12% protein (480 grams). This horse would now be eating 1,280 grams of protein—despite not actually switching feeds—and consuming levels an intensely working horse would need.
Protein is an important source of the amino acids required for skeletal muscle synthesis, and these needs do increase with workload. While the percentage of protein on the bag might not matter much, the amino acid quality is very important. Manufacturers of performance horse feeds should either list their lysine (and perhaps other amino acid) content or soybean meal or another high-quality protein source on their ingredient list.
Feeds designed for athletic horses also tend to be higher in calcium and phosphorus than those for nonworking horses, because bone remodeling occurs during exercise and these minerals are required in higher amounts for this process.
These feeds likely also have vitamin E added because it is an antioxidant, which might help counteract muscle damage from exercise, and the ingredient list will reflect alpha-tocopherol or simply vitamin E. Horses (unlike humans) don’t generally require ascorbic acid (vitamin C), but performance horse feeds often include it because of its antioxidant properties.
On the ingredient list you might also see fat sources that are high in omega-3 fatty acids, such as linseed (flaxseed) oil or even fish oils. Such fats help fuel the body through metabolism and could also combat inflammation.
Owners and trainers preparing horses for exercise and competition should work closely with their equine nutritionist and veterinarian to select the performance horse feed best suited to their needs.