Does Your Horse Need Probiotics?

If your horse’s gut microbiota is out of whack, microorganism-packed products might get him back on track

Inside the digestive system live millions of microscopic organisms that play vital roles in the horse’s digestive—and general—health. Many of these of bacteria, protozoa, archaea, and fungi help break down food and usher nutrients efficiently into the bloodstream. They play a role in metabolizing fiber, generating energy, and promoting proper intestinal transit.

While scientists still don’t know what makes up the ideal equine gut microbiota, they do know it’s a question of balance. “All these microorganisms live in a kind of symbiotic relationship when they’re in balance,” says Kathleen Crandell, PhD, a nutritionist with Kentucky Equine Research, in Versailles.

Without listing the thousands of species or labeling certain microbes as good or bad, let’s briefly say the “right” balance includes more Lachnospiraceae and Ruminococcaceae bacteria, which break down plant materials, and fewer Streptococcus and Lactobacillus bacteria, which produce lactic acid, Crandell says.

When that balance gets disrupted, so too does the symbiotic relationship, she explains. Horses might have intestinal discomfort, develop diarrhea, lose weight, experience energy loss and poor performance, seem generally unwell, and become more susceptible to illnesses.

To help shift that balance back in a direction that favors good health, scientists have isolated certain species of microorganisms from the microbiome and packaged them into oral powders, pastes, and liquids. These are probiotics.

You often see probiotics and prebiotics (fiber sources for the microbiota to break down, or “food” for the probiotics) packaged and supplemented together, but for the purpose of this article, we’ll focus on the former.

Assessing Safety and Efficacy

Study results show probiotics are safe for most horses, Crandell says. But while in theory they should work, little hard scientific evidence shows they are beneficial.

Most of the important digestive action in horses occurs in the cecum and colon—the hindgut—where fiber, in particular, the mainstay of equine nutrition, gets broken down, says Simon Daniels, PhD, senior lecturer of equine management and science at the U.K.’s Royal Agricultural University, in Cirencester. It’s here probiotics need to work their magic most, ideally reversing upsets in the favorable ratios between microorganism

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