By Nickie Polson

Horses are built to eat grass. Their digestive systems are ideal for getting the most out of a fairly low energy food source.
Grazing horses eat slowly, chew carefully, and may eat for 16 – 18 hours a day. Food moves through them almost constantly, as anyone who has ever cleaned up after a horse will have noticed.
The health of a horse’s digestive system is crucial to the health of the animal. First, the mouth and teeth must be in fine working order. Then the stomach must do its part with acids and enzymes. The small intestine is where many nutrients are digested and absorbed into the blood. Finally the remaining material goes into the large intestine, where healthy bacteria digest what’s left of the food, so that the horse can make use of it. Anything left over gets pushed out the other end.

Since most of our horses are not spending their lives on natural pasture, the more we know about keeping all these steps working well, the better.

Horses chew about 60,000 times a day. Chewing is a ‘pre-treatment’ to get digestion started. A horse that cannot chew well does not get full benefit from its food. A horse’s teeth should be checked once a year, and more regularly for older horses.

Because horses are built to eat almost constantly, their stomachs are small. One cause of colic is eating too much at one time. However, if a horse’s stomach remains empty for too long, gas is produced which can damage the stomach.

Acids and enzymes in the stomach break down the food. If the food was not well-chewed to begin with, this will not be as effective since food stays in a horse’s stomach for only 20 minutes or so. Only a small portion of the nutrients is absorbed in the stomach.
Once food gets into the 75 foot-long small intestine, real digestion begins. Here the stomach acids are neutralized with bile and other secretions. The digestive enzymes that cannot survive in acid are added. Food spends between one and eight hours in the small intestine. Protein, fat, and roughly half the carbohydrates are absorbed.

The digestive enzymes that a horse secretes are delivered in response to a particular kind of food. When a horse’s food changes, the enzymes needed may change. This is why it is often recommended to make changes slowly in a horse’s diet, so the enzyme production has time to adapt.

The large intestine is about 25 feet long, but is very wide. It is home to a large amount of partially digested food, water and microbes. Basically, this is a fermentation vat where billions of good bacteria and protozoa work on digesting cellulose in the remaining fiber. This is where the horse gets essential volatile fatty acids. This digestion can take 50 – 60 hours.

Those microbes can be upset by changes in the horse’s diet, which is another reason to only slowly change what a horse feeds on. A sudden large input of grain or green grass (high starch) into the large intestine may cause the bacteria to produce acid and die. When they die, they release toxins that can cause colic or laminitis.
Grinding or chopping feed increases the rate of passage through the stomach and small intestine, decreasing the absorption of nutrients there. When these nutrients get to the large intestine, they can be quickly fermented, potentially causing colic or founder.
The usual recommendation is to feed at least two or three small meals of grain per day with plenty of hay, pasture or chaff. A horse that is not working too hard can manage well on a diet of hay or pasture alone. The more natural roughage fed, the better the digestive health of the horse.

Since bacteria make a vital contribution to a horse’s digestive health, keeping those good bacteria healthy is yet another part of good horse-care. That will be my topic for next month’s column.
………………
npolson@uniserve.com