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Equine Nutrition and the Use of Probiotics


Twenty years ago, a 20-year-old horse was considered an “old timer.” Today, it is common for a horse of that age to be productively working. Together with vaccination, deworming, and dental care, advances in understanding of equine nutrition are responsible for the increased longevity of our horses. We know so much more about the nutritional needs of horses than we used to. Feed companies are meeting the nutritional needs of everything from the companion animal to the high-performance athlete with a great variety of products. As feed products have improved, the focus has moved to feed utilization, or getting the most out of those products. Talking about feed utilization means talking about the bacteria located within the equine gastro-intestinal tract.

The Microbiome

Microbiome and microbiota are the two mostly commonly used terms referring to the bacteria normally found within the gastro-intestinal tract. Newborn horses, even before they stand and nurse, share about 80% of the dam’s microbiome. Over the course of the horse’s first two months, the microbiome changes to match about 95% of the dam’s microbiome and continues to get closer for up to one year. Weaning does not change this microbiome development process to any great extent.
There isn’t much debate over the function of the microbiome and its importance for both gastro- intestinal health and overall immune function. Establishing a “normal” microbiome has far- reaching effects on the immune system later in life. “Dysbiosis” (i.e., the gut bacteria are out of whack) likely plays a significant role in the development of gastro-intestinal diseases, including inflammatory bowel disease.

Where there is debate is over whether adding probiotics to a horse’s diet benefits feed utilization and gastro-intestinal health. Here is a short review of the important findings.

A Variable Product

Digestive supplements may contain prebiotics, probiotics, or a combination of the two.

Prebiotics are non-digestible food ingredients that promote the growth of beneficial bacteria in the intestine. These ingredients are usually simple sugars called oligosaccharides and, unlike probiotics, do not contain live bacteria. (Prebiotics are a whole different topic for another day.)

Probiotics contain living organisms, but quality control of over-the-counter probiotics is not tightly regulated. Studies testing label claims found that few probiotic products contained the number of bacteria they claimed. Unless the manufacturer has undergone lab testing to confirm there are still active cultures by the expiration date, a probiotic supplement is unlikely to have any value.

Also, many probiotic bacteria require storage in a temperature-controlled environment to remain viable. Make sure you follow the product’s storage instructions, refrigerating the product if necessary and using it before the expiration date.

Feed Utilization

While there isn’t as much literature available on the horse as for other species, there is evidence to suggest that using a probiotic can increase feed digestibility. Interestingly, just some parts of Lactobacillus bacteria, rather than live cultures, can be effective. In cattle, efficiency (meaning the ability to absorb nutrients from the feed into the body for use) is increased close to 15% by probiotics. In the horse, increased appetite has been observed, especially when diets are changed.

Immune Function

Research has documented several effects of probiotics that are important for sustained equine health. Some commensal (naturally found) Lactobacilli and Bifidobacteria can regulate intestinal function and help prevent diarrhea. Researchers even found a molecular reason for this effect. Other research demonstrates that probiotics have some effect on systemic immunity, specifically proliferative responses, immunoglobulin G concentrations, and neutrophil numbers. This leads some to think probiotics can “balance” the immune response, so that the response is not over or under reactive.

Improved GI Health

Research has also shown that oral administration of some fermentation-promoting probiotics may improve the intestinal environment biochemically and microbiologically. This means that probiotics may help “normalize” microbiomes that have been perturbed by stress or antibiotics. Additionally, some probiotics increase the ability of psyllium to help move sand from the gastro-intestinal tract in cases of sand colic, meaning that these products might improve gastro-intestinal motility. Abnormal bowel motility is a leading culprit in causing colic.

GI Disease

A commonly used probiotic, Saccharomyces boulardii, has been shown not only to support a healthy gut environment but also to inactivate C. difficile toxins. A study evaluating the effect of S. boulardii in horses with acute enterocolitis found that the severity and duration of gastrointestinal disease during hospitalization were significantly decreased in horses receiving S. boulardii compared with the placebo.

Adverse Effects

Any live product should be used with caution, especially when dealing with foals. In foals the microflora that will be vital to immune function later in life are still developing. Though adverse reactions from probiotics are rare, effects such as diarrhea have been reported in foals. A recent study showed that prophylactic probiotic treatment did not reduce incidence
or duration of diarrhea in neonatal foals but instead could have contributed to prolonged disease.


Clearly, a sound nutrition program is vital to the success of any equine athlete, and quality feed is a major expense in any operation. Science now appears to point to probiotics as helpful in maximizing the effect of nutritional programs. Of the several commercially available products, those derived from Lactobacillus species appear to work the best, and they might not need to be live cultures to produce beneficial effects. When choosing a product, lean towards the companies with the most experience and best data to support their use.

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Pilchuck Veterinary Hospital


11308 92nd St SE Snohomish, WA 98290


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