Forage, fermentation, saliva & digestation
Feeding In Hot Weather
There are basic principles that apply when feeding the horse. These are true when the horse is on pasture or in confinement. I would like to discuss these, and then try to explain how the needs of the confined horse are different.
Before domestication by Man, the horse survived by grazing. Their digestive tract was and still is made to utilize forages for the nutrients the horse needs to survive. The random salt deposit and eating dirt provided the minerals lacking in the grass. The range consisted of a mixed population of grasses. Except during winter, there was usually some grass in the growing stage.
Whether the grass was growing or in winter dormancy, the horse had to chew it after biting it off. The chewing process allows the mixing of the forage with saliva inside the mouth. Saliva helps a bit with breakdown of the forage, but is an especially important source of lubricant and buffer. The purpose of the lubricant becomes obvious as the bolus (the chewed grass that accumulates into a wad to be swallowed) moves down the esophagus into the stomach. Within the stomach, the presence of food stimulates acid release. The acid helps to break down the fibers of the grass or hay. Fortunately, on a high roughage diet, the buffer of the saliva neutralizes this acid before it can damage the lining of the stomach.
Once the roughage moves from the stomach to the small intestine it starts breaking down, and its nutrients are absorbed through the intestine wall and into the blood stream. There are always some fibers that are not digested. The more mature the forage, the higher the percentage of indigestible fibers. This has an effect on the stool. When the grass is lush and rapidly growing it is low in fiber. As a result the stool will be more liquid, due to both the high moisture content of the grass and its rapid movement through the bowel. With a higher fiber content, the stool will be more formed. Some fiber is important to provide bulk for bowel movement. It is within the large bowel that some fermentation occurs. The result is a supply of B vitamins that are absorbed through the gut wall. The other product of this fermentation is gas. Other than the annoying noise it makes when the horse runs and bucks, and the small amount of methane it contributes to global warming, it is of little importance as long as the bowel is moving and it continues to be passed. It is only when the bowel slows or stops from dehydration, lack of exercise, or pain that the gas accumulates and starts to stretch the intestine. This causes a great deal of discomfort and can lead to signs of colic.
Digesting roughage takes much longer than the digestion of concentrates. The fibers must be broken down to a form that can be absorbed. It may be all the way into the large intestine before the last of the usable nutrients are freed. The process of breaking down fibers generates heat. This “heat of metabolism” is a detectable amount of energy that warms the horse. This is great in the winter when the digestion of forages increases the body temperature a degree or two for a period of several hours.
Grains do not take long to digest because they have few indigestible fibers. They cause a brief rush of energy, and are soon digested and gone. This is great in the summer. Also, grains are not inside the mouth very long for the same reason. They still, however, stimulate a great deal of acid release within the digestive part of the stomach (the stomach is divided in the horse, one part for grinding and the other for digestion). When the grain is fed without a side of salad, there is little buffer to help neutralize this acid. A high acid level causes a great deal of irritation to the stomach.
By now, you have probably heard about all you ever wanted to know about the inner workings of the horse.
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