In the spring and fall, pasture grass contains more simple carbohydrates (sugars) than in the summer and winter, which can complicate horse feeding. This can mean problems for your horse, especially if you're also feeding him grain. Here's how to adjust your horse feeding in the fall to avoid digestive upset, including life-threatening colic.
It's About the Bugs
Your horse's large horse intestine is essentially a fermentation vat. Hind-gut bacteria and protozoa in the large horse intestine break down nutrients. Your horse then absorbs and uses the byproducts of that breakdown: proteins, fats, and carbohydrates.
Each specific type of intestinal organism (and there are hundreds) need a specific type of food to survive in the horse intestine. Some are better at using complex fibers. Some like simple sugars. Others will thrive on high protein. Still others will further break down the products produced by other types of organisms.
When your horse's intestinal organisms (or bugs) receive a constant flow of foods to ferment in a high volume of fluid, they can adapt to changes much easier.
But when a large load of fermentable food that's different than normal hits the hind gut all at once, there can be a rapid increase in the "bugs" that prefer that type of nutrient. This, in turn, can change the chemistry in the intestine and cause other forms of bugs to die off. When this happens, your horse can suffer anything from gas, mild distention, and diarrhea, to full-blown colic.
And if the large intestine becomes too acidic, as it can if unusually high amounts of sugar, starch, or complex plant sugars enter it, the lining can become damaged and bacterial toxins absorbed into the body. This can make your horse very ill and can even cause laminitis.
You likely already know that if you start, increase, or change grains rapidly you risk intestinal upset. However, you might be surprised to learn that changes in hay can be bad, too.
The large intestine is the major site for breakdown of hay. Even if you always feed the same type of hay, such as timothy, Bermuda grass, or alfalfa—not all hay is created equal. Cuttings, growth conditions, and even different strains of the same type of forage can vary the level of rapidly fermentable nutrients they contain.
And changing hay types is even harder on your horse's system.
Your pasture grass also changes composition in the spring and fall, when it grows rapidly and experiences a spike in simple carbohydrates (sugars). High protein levels in young, growing pastures can also cause gut upset.
These six guidelines can help you prevent feeding-related gut upsets.
• Introduce grain feeding gradually, no more than one pound per feeding.
• Allow three days between each increase in grain to enable the intestinal bugs to adapt.
• Don't feed more than four pounds of grain at one time.
• Make changes in hay gradually, replacing from 10 to 25 percent of the old hay with the new variety; increase the percentage of new hay every three days.
• Accustom your horse to lush pastures gradually, especially if grass is growing rapidly in the spring and fall.
• If your horse is on young growths of pasture grass, feed him hay to provide complex and slowly fermented fiber that the grasses may be lacking.
Eleanor M. Kellon, VMD, works as a writer, teacher, and internal medicine/nutrition consultant. Prior to this, Dr. Kellon has had more than 10 years' experience in private practice. She also has extensive experience with performance horses. She's based in Pennsylvania, where she and her husband raise, train, and race Standardbreds. Her most recent book is Horse Journal Guide to Equine Supplements and Nutraceuticals (Globe Pequot Press).