Good Bugs Versus Bad Bugs

Probiotics seem to be all the rage these days. Are these yeast and bacteria really a good thing for a horse’s gut?

Long before the existence of nutraceuticals, there were probiotics. The term, taken from the Greek words for “for” and “life,” refers to yeast, bacteria and associated enzymes that enhance the growth of naturally occurring flora in the horse’s gut that aid digestion. We’re talking about good flora here, not the deadly microbes that exist in minute amounts in a horse and do not need any encouraging. As with most systems in living things, whether human or animal, a “delicate balance” of good and bad is necessary. Probiotics play a role in maintaining that balance.

Who Should Use Them?

“Probiotics are often called into play when horses have been taking a lengthy course of antibiotics,” says Dr. Ginger Rich, PhD, a respected expert in the highly specialized genre of probiotic equine nutrition. “Antibiotics may kill good bacteria that we don’t want to die. Probiotics can re-establish requisite hind gut bacterial populations.” Dr. Rich, formerly of Colorado State University and now a consultant living in Memphis, Tenn., and St. Thomas, U. S. Virgin Islands, also recommends probiotics for horses whose stress levels are high, such as those competing or racing very frequently or traveling a great deal.

At the very least, probiotics may help your horses obtain the best nutritional benefit from their food, which may in turn improve their ability to ward off diseases. They might just look better, too, with a renewed shine to their coats and sparkle to their eyes.

Even though probiotics are being widely used, especially in high-level performance horses, you won’t find loads of substantive research on them. Not that there’s anything to worry about. “They’re quite benign, so perhaps the only thing they’ll generally hurt is your pocketbook,” she says. She cited several past research projects and in-progress case studies “that do look very promising and show some interesting trends in the results.”

“If no research results exist, you might assume they’ve not spent the money to do it.”

That said, Dr. Rich uses probiotics only in certain situations, such as with antibiotic use or with animals that don’t keep weight well. She declines to recommend specific brands, but she delineates the two main types of probiotics, yeast and bacteria.


Live yeast aids in breaking down fibers, which is mainly what horses eat. Although supporting research for yeast efficacy is admittedly “pretty thin,” Rich likes the way it keeps microbes healthy, especially in the hind gut. So she’ll include it in a finished grain ration, and likes to think it may ward off both diarrhea and colic, especially in herds of broodmares and babies or in hard-working or traveling animals.

“Live” yeast cultures come in liquid, paste and powder forms. Look for cultures that include Saccharomyces cerevisiae and Aspergillis oryza. (Don’t let names intimidate. Instead, get familiar with them to be a savvy shopper.) And yes, dry products, such as powders, can contain active cultures. “Many dried yeast cultures are still alive,” Dr. Rich says.

Live yeast cultures are best known for their presence in yogurt, and Rich doesn’t hesitate to recommend the creamy concoction if a horse has certain types of diarrhea. “Citrus fruit flavors are more palatable,” such as Key Lime and Passion Fruit/Orange, she said. Yogurt is usually given via syringe, six to eight ounces, twice daily. Caution: Make sure the container label denotes live cultures.


Many bacteria play a positive role in humans and horses. Some names you might recognize include Lactobacillus acidophilus and Streptococcus faecium…all are year-round residents in an equine gut and invaluable activists in fiber and protein digestion, helping each other synergistically by actually being “in competition” with one another, according to Rich.

“They’re quite benign, so perhaps the only thing they’ll generally hurt is your pocketbook.”

She explains that each variety of bacteria has its own specific role in breaking down feeds. In addition, bacteria are very particular about their diets. When the substrate or feed that a specific bacteria uses is removed from the horse’s diet, not surprisingly, that group of bacteria dies. Upon death, it gives off endotoxins that can cause severe digestive upset, including colic or founder. It may take weeks to re-establish the population. This is why gradual ration changes are advised instead of immediately switching products.

If you’ve decided you want to add probiotics to your feed, what is your next step? “Talk to your veterinarian or nutritionist to decide if your horse or herd really needs them,” says Rich. “Do some label reading and price shopping before you buy. Look for a company that’s well established, with quality control standards. Ask, ‘Have they done research, sponsored with a third party? Have they gotten good results, and have they posted them on their website?’ If no research results exist, you might assume they’ve not spent the money to do it. Or perhaps the results were negative.”

As a horse professional in 2004, you are so much more informed than you might have been a decade ago. With so much information available, though, the array of choices can be dizzying. Still, be glad you have them—you and your horses only stand to benefit.






Oops! We could not locate your form.