When evaluating a horse's ration, remember that forage contains protein, too. Typical levels in grass hays range from 3 to 14 percent, and there is even more in alfalfa--at least 18 to as much as 25 percent. Most horses in light work will do just fine with a feed that supplies a lower amount of crude protein, especially if they are also receiving any amount of alfalfa hay in their diet.
Crude fat is one indicator of a feed's energy content. Fat provides nearly 2.5 times as much energy, pound per pound, than carbohydrates or protein--the higher the crude fat, the more calories the feed provides. Fats are burned as fuel, but they are also important to the diet as carriers for fat-soluble vitamins, and they form certain essential fatty acids, which aid many cellular functions.
I find that people tend to overlook the crude fat content, which can tell you how many pounds of feed a horse needs. If it's a higher energy feed, you need to offer a lot less to provide the same amount of calories.
Most grain-based feeds provide between 2 and 4 percent crude fat, but some formulated for energy contain as much as 14 percent. Horses digest fats more safely and efficiently than they do starch, and if an individual needs the extra calories, it's better to provide the same quantity of a higher fat feed than to simply increase his portion of starchy grains alone.
Crude fiber consists of the carbohydrates that are not digested or absorbed for use as fuel or to build body tissue. Horses are designed to be forage eaters, and a high-fiber diet is crucial for normal digestive tract function.
Indirectly, the crude fiber level on a feed tag is the single best indicator of energy content, even more so than crude fat. Fiber provides energy, but only at very low levels when compared to soluble (digestible) carbohydrates or fat. So as fiber content goes up, the energy content goes down. More specifically, the crude fiber percentage tells you how much of the feed consists of grains--which ranges from 2 percent for energy-dense grains such as corn to 12 to 14 percent for bulky grains such as oats--and how much consists of hays and other forage that are high in fiber.
Concentrate mixes containing less than 7 percent fiber are dense in energy and must be fed with great care to avoid overloading the horse with starches, which can lead to laminitis. Concentrates with 8 to 11 percent fiber are moderate in energy, while concentrates with greater than 12 percent fiber are low in energy. Feeds with higher amounts of crude fiber are best for most adult horses in light work.
Calcium and phosphorus, taken together, are probably the two most crucial mineral levels to note on a feed tag. They play a vital role in the health of the musculoskeletal system. All horses need calcium and phosphorus in their diets, but youngsters and broodmares in particular require higher levels of these nutrients.
A feed formulated for weanlings ought to have at least 0.7 percent calcium and 0.4 percent phosphorus, whereas an adult horse in average work requires only 0.3 percent calcium and 0.2 to 0.5 percent phosphorus. Most commercial feeds supply more than these minimum requirements. Levels as high as 0.9 percent calcium and 0.8 percent phosphorus are common, but they may range as low as 0.4 percent and 0.3 percent, respectively.
But just as important as the total quantities of each nutrient is the ratio of the two minerals to each other. A horse needs to consume 1.1 to 2 parts calcium for every part phosphorus in his diet. That's because the body needs an equal part of calcium in order to absorb phosphorus, and if that calcium is not present in the diet, it will be taken from other places--such as the bones--to accomplish the job. Although excessive calcium in the diet can lead to gastric ulcers and other conditions, it's generally better to err on the side of too much of this nutrient than too little--horses can tolerate as much as five to seven times the recommended calcium with no ill effects, so long as they also get adequate phosphorus.
Keep in mind that your horse will also be consuming minerals in his forage. Legume hay, such as alfalfa, is much higher in calcium than grass hays. Thus, if alfalfa is a staple of your horse's diet, he doesn't need as much calcium in his feed, and vice versa. Some feeds are formulated to complement different sources of forage; the label will specify whether it is meant to be fed with grass or alfalfa hays.