Colic and other digestive upsets are a common problem in horses and a variety of over-the-counter supplements are available to deal with them. Probiotics and prebiotics focus on large intestinal function, where complex components of feeds are fermented rather than digested. Other supplements address gastric acidity and ulcers. This article will focus on supplements that aid the digestion of food in the upper intestinal tract, which is between the stomach and the large bowel.
Digestion begins with chewing, which breaks the food into smaller, easier-to-digest particles. During the chewing, the food is also moistened by saliva. The horse can secrete as much as 50 ml (almost 2 oz.) of saliva per minute. Unlike in other species, equine saliva doesn’t contain significant amounts of the enzyme amylase, so it doesn’t directly help digestion, but it does contain mucin to lubricate the passage of dry foods, has electrolytes and is high in acid-buffering bicarbonate.
The bicarbonate in saliva is important in protecting the upper portions of the stomach from ulcers. It also lowers the pH enough in the upper stomach that fermenting bacteria can survive there and get a jump on the process of breaking down components of hay and grass that the small intestine can’t digest.
The next digestive stop is the stomach. How long foods stay in the stomach depends on particle size. Larger particles will be retained in the buffered, upper portions of the stomach, where resident bacteria can begin their breakdown by fermenting them, just like they do in the large bowel. In the lower portion of the stomach, just before the small intestine, stomach acid and the enzymes lipase and pepsin are secreted. These begin the process of breakdown of protein and fat.
After release from the stomach, the now-fluid food passes into the duodenum, the upper portion of the small intestine. The pancreas empties its secretions into the upper duodenum. Pancreatic secretions contain large amounts of bicarbonate to neutralize the stomach acid.
They also contain the digestive enzymes amylase, lipase and pepsin, but in much lower concentrations than other species. This is because the horse evolved on a diet of grasses, which is largely not digestible in the small intestine. (That is also why it’s important never to overfeed grain. Three to five pounds of grain per meal should be the upper limit.)
Bile from the liver also enters the upper duodenum. Bile helps neutralize stomach acid and aids the digestion and absorption of fat.
The constant secretion of large amounts of bile in a horse’s small intestine, coupled with a surprisingly high output of lipase by both the stomach and the pancreas, is responsible for the horse being able to utilize larger amounts of fat than would normally be found in an equine diet. The mixture of food, water, electrolytes, bile and digestive enzymes then moves into the jejunum and ileum, where absorption of the digestible portion of the food occurs.
Looking at this by type of nutrient:
Protein: Proteins are broken down by stomach acid and pepsin. Pancreatic enzymes in the small intestine finish the job of breaking proteins down into amino acids, which are then absorbed across the bowel wall.
Carbohydrate: The upper stomach begins the breakdown of carbohydrates. Carbs fermented here are converted to lactate or other volatile fatty acids, just like they are in the hindgut. These are easily absorbed in the small intestine and travel to the liver and other body tissues, where they can either be burned directly as fuels or converted by the liver to either glucose or fatty acids.
Carbohydrates that escape stomach fermentation are acted on by amylase from pancreatic fluid. Amylase breaks starch down into simpler sugars, which are in turn broken down into glucose or fructose before being absorbed by a process that requires sodium to get the sugars across the intestinal lining.
Fat: Most of the fat in the diet, whether added or naturally present in low levels in grains and forages, is in the form of ”long chain” fats. Bile acids bind to and emulsify these fatty acids so that the fat digesting lipase enzymes can work on them. The fat-soluble vitamins, which include vitamins A, D, E and K, are absorbed along with the digested fats.
The last step is moving the digested nutrients across the intestinal wall and into the body. Most of these transport processes require sodium to function.
Before looking at supplements targeting digestion, a quick review of things that might contribute to digestive problems is in order:
1) Parasites can be involved in a wide variety of intestinal-tract symptoms, including bloating, poor utilization of foods, even poor appetite or colic. Consult with your vet to formulate an appropriate monitoring and deworming schedule for your horse. Very young and old horses are especially susceptible to parasites and need more intensive deworming.
2) Water and salt. We don’t often think of these in connection with digestion, but the digestive tract secretes massive amounts of fluids and electrolytes, both from digestive organs like the salivary glands, liver and pancreas, and also by the lining of the intestine itself. Adequate salt intake is critical to maintaining normal water levels in the body and provides the sodium needed for the active uptake of digested foods.
3) Types of food. Don’t make the mistake of thinking of hay as ”just roughage” and grains as your horse’s real food. Grains have their place, but the horse’s digestive tract is designed to run on grass/hay. Many breeds can easily maintain their weight on hay alone and can have any protein or mineral balancing needs met by supplements rather than large feedings of grain.
Softening of manure is the most common symptom of grain overfeeding. These horses also often become sluggish, bloated, gassy, irritable and perform poorly. You would, too, if you were dealing with nagging belly pain. When stressed or excited, the soft manure can become obvious diarrhea. Adjusting the size of grain meals may be all that you need to do. Pro- and prebiotics also help restore populations of micro-organisms that are killed by the drop in large bowel pH resulting from fermentation of grains.
Free-choice hay is best, and all horses should receive a bare minimum of 1% of their body weight in hay per day, preferably 1.5 to 2%. Your horse’s forage is important for natural acid-buffering processes.
Optimizing your horse’s digestive comes down to having a good game plan. We recommend that you:
1) Ensure adequate water and salt intake, and make sure there are no dental problems requiring correction.
2) Make sure your horse is receiving an adequate supply of forage (grass or hay), to encourage good saliva production and buffer the intestinal tract.
After that, for horses that don’t chew well, bolt their food, are on processed forages or grains, or have a tendency to choke, consider adding a lubricating agent to replace the mucin that saliva provides. Psyllium is our choice here for both price and mucilage content. Herb N Horse and Uckele both make reasonably priced psyllium products. We like the Uckele resealable tub, however.
Bolters and poor chewers on processed forages or grains may also benefit from replacement of buffers they would otherwise normally get from saliva. Saliva contains rapidly acting bicarbonate (aka baking soda). Most horses find this unpalatable but may accept 1 or 2 teaspoons in a meal. If not, you could try our pick of equine calcium/magnesium-based antacids, U-Gard (www.corta-flx.com, 888-294-1100).
Check with your vet about the adequacy of your deworming program. If the horse is not gaining weight on what should be enough food, make sure you are not overfeeding grain and underfeeding forage. If the diet is OK, try adding a good pre- or probiotic like Ration Plus or Equine Generator.
If you’ve followed all of recommendations above, and the horse is still having digestive upset or can’t gain weight, the horse may benefit from digestive enzymes. In that case, our choice is Absorb All, if the horse is already on a bacteria supporting pre/probiotic or didn’t respond to one in the past.
Otherwise, we recommend you consider trying Equine Generator, if you want to combine high potency prebiotic support with high levels of digestive enzymes for a comprehensive approach to your horse’s care.