Older horses who have problems maintaining weight are good candidates for digestive supplements. Prebiotics based on fermentation products of Lactobacillus have been documented to improve weight gain and feed efficiency.

If you pick up any bag of horse feed—and many of the nutritional supplements as well—you’re almost certain to see a long list of Latin words in the ingredients. Names like Lactobacillus, Enterococcus, Bifidobacterium, Saccharomyces, and more are listed. These are the Latin names of some of the beneficial bacteria and yeast present in your horse’s intestinal tract. When these bacteria and/or yeast are given to the horse orally as live microorganisms, they are called probiotics.

Prebiotics, on the other hand, are substances that don’t contain the actual organisms, but do encourage their growth. As an example, fermentation products are liquids or dried concentrates of fluid that are extracted from vats where beneficial types of organisms are growing. These products are believed to contain factors that encourage beneficial strains to proliferate and thrive.

Another example is soluble fibers—such as beet pulp and complex plant carbohydrates. These can also be considered prebiotics because they are easily fermented. In fact, the grass and hay portion of your horse’s diet is probably the most important prebiotic, since beneficial organisms cannot thrive without something to "eat."

Supplementing with Microorganisms
Your horse is getting "supplemented" with microorganisms with every bite of food he eats. This is because food is not sterile—especially raw food. Microorganisms abound on the ground, on the feeder you use for hay, on the hay itself—everywhere. In fact, ingestion is how the organisms get into the horse in the first place. Interestingly, foals and horses with intestinal upsets will often instinctively supplement their microorganism intake themselves by eating manure.

So do you really need to give your horse more microorganisms? The answer is both yes and no. A horse who is holding weight well, has normal-looking manure, and doesn’t experience intestinal tract problems is not likely to benefit from a prebiotic or probiotic. These products won’t hurt him, but he won’t benefit either.

When Can They Help?
Some situations when prebiotics and probiotics can be helpful are:

• Before and during weaning, to help the young horse’s transition to a fully solid diet
• After very hard exercise or long-distance shipping, to help the microorganism populations get back up to their normal levels
• When the horse is receiving antibiotics, to help prevent die-off of microorganisms
• During the treatment of diarrhea or after treatment for colic
• When older horses are having trouble maintaining their weight
• When horses are on high-grain diets, especially if they have any gastrointestinal tract upsets or loose manure

Instances when you might see prebiotics or probiotics recommended, but they are not likely to be helpful, are:

• During deworming—deworming drugs don’t hurt the intestinal bacteria.
• Before shipping or heavy exercise. High body heat from heavy or prolonged exercise and rapid transit time during shipping (excitement can cause this) will harm the microorganisms.

In these instances, it would be better to give supplements afterward to help recovery.

As you prepare your foal for weaning, consider adding prebiotics or probiotics to his diet to help him transition to eating only solid food. Maintaining the added supplement during the weaning process can also help the gut handle some of the stress generated during this time.

Using These Products
Either prebiotics (substances to encourage microorganism growth) or probiotics (live microorganisms) can be used in most cases. Saccharomyces yeast is specifically helpful in preventing acidity in the large bowel of horses on high-grain diets. Unfortunately, we don’t have much research information to guide the use of these products. Prebiotics based on fermentation products of Lactobacillus have been documented to improve weight gain and feed efficiency. Beyond that, we don’t have much equine-specific information to go on.

Dose, however, is a critical factor. Dr. Scott Weese of the Ontario Veterinary College at the University of Guelph in Canada is an expert in probiotics. He has estimated that the very minimum effective dose of live microorganisms for a horse would be in the neighborhood of 10 billion CFU. A CFU is a "colony forming unit"—that is, one live bacterium. When you consider that just a teaspoon of colonic fluid can contain as many as 15 million bacteria, it’s not too hard to see where that number comes from. Most bacteria are actually killed by stomach acid. If they make it through the stomach, they can quickly multiply, but not too many make it through. If you are considering using a live probiotic product, be sure to check the dose of microorganisms.

Another factor is stability. High-quality human probiotic products not only contain very high numbers of microorganisms (usually more than the 10 billion CFU noted above), but they are also kept refrigerated to prolong the life of the bacteria. Dr. Weese did a study of 13 probiotic products and found that only two actually contained the number and types of bacteria they claimed.

The concerns about dosage and stability can make a prebiotic product a better choice in many instances than a probiotic product. If you are going to use a live-

organism probiotic, though, make sure it has a high enough dose and then store it well-sealed in a cool area.