Monthly Topic: Microbiome

Last month I began the new monthly themes with the digestive system. It seems like a natural progression, then, to move forward and hone in a bit more on the digestive tract. This month? The equine microbiome.

Missed last month? Here are the links:

Monthly Topic: The Digestive System

Fast Facts About The Equine Digestive System

It’s a well known fact that we all have billions of microorganisms inhabiting our body. We rely on the mibrobes in our gut to help us process and digest our food. As hindgut fermentors, horses rely on their gut microbes even more.

The horse is host to as many as a quadrillion microbes in the digestive tract. Different parts of the tract are host to several different types of “bugs.” In fact, one study from 2001 even suggested 89% of the DNA they pulled from microbe samples were unknown. The scientists that study these parts of the equine world only have a few options to collect samples from their living subjects. Most often, contents from the stomach (pre-cecal) or the fecal matter are examined. Pulling sampled from the hindgut is difficult/impossible to do on a living subject; most of the studies that I’ve read have taken samples from recently euthanized horses.

Microbiota can be separated into different classes; proteolytic, cellulolytic, glycolytic, and lactate-using. In other words, the primary function of these bugs are breaking down protein (proteo), fiber (cellulo), starch/sugars (amylo), or using lactate. Since horses eat hay and forage it should stand to reason that we would see more cellulolytic bacteria, right?


The cecum (where most long-stem forage is digested) is comprised of about 78% cellulolytic bacteria, and only 22% proteolytic bacteria.

A healthy gut is more than just a horse with solid poops and good weight. For many years science has linked gut microbiome to the central nervous system. In humans with depression, fecal samples suggested lower/altered biodiversity than in humans without (aren’t you glad you don’t have that job?). In another study mice with altered gut microbes showed more anxious behaviors. But what about horses?

An article from 2019 studied horses fed forage only for 30 days. They were then transitioned to a Hay/Barley diet. In the behavioral study researchers noticed more blowing (snorting) from the horses during the hay/barley diet phase which would suggest more anxiety-driven behavior. Additionally they found more amylolytic (starch/sugar) bacteria. Specifically among the amylolytic bacteria was Succinivibrio family amylolytic bacteria….the cecal microbiome has shown to have elevated Succinivibrio dextrinosolvens prior to the onset of laminitis.

That’s not all. In humans disturbances in the gut microbiome has been noted in various other disorders; metabolic issues, mental health issues, rheumatoid arthritis, irritable bowel syndrome, and even some forms of cancer. Horses are similarly affected even though less information is available about it. Changes in the equine microbiome have been noted in colitis, equine grass sickness, colic, laminitis.

In short, a healthy horse has a healthy microbiome…just because we can’t see it exactly doesn’t mean we can ignore good gut health.


  • Kauter, A., Epping, L., Semmler, T. et al. The gut microbiome of horses: current research on equine enteral microbiota and future perspectives. anim microbiome 1, 14 (2019).
  • Ericsson AC, Johnson PJ, Lopes MA, Perry SC, Lanter HR. A Microbiological Map of the Healthy Equine Gastrointestinal Tract. PLoS One. 2016 Nov 15;11(11):e0166523. doi: 10.1371/journal.pone.0166523. PMID: 27846295; PMCID: PMC5112786.
  • Santos AS, Rodrigues MA, Bessa RJ, Ferreira LM, Martin-Rosset W. Understanding the equine cecum-colon ecosystem: current knowledge and future perspectives. Animal. 2011 Jan;5(1):48-56. doi: 10.1017/S1751731110001588. PMID: 22440701.
  • Destrez, Alexandra & Grimm, Pauline & Julliand, Véronique. (2019). Dietary-induced modulation of the hindgut microbiota is related to behavioral responses during stressful events in horses. Physiology & Behavior. 202. 10.1016/j.physbeh.2019.02.003.
  • Julliand, Véronique & A, de & Varloud, Marie. (2006). Starch digestion in horses: The impact of feed processing. Livestock Science. 100. 44-52. 10.1016/j.livprodsci.2005.11.001.


  1. Great info, Thankyou for taking the time to do research it must take you ages. I was just talking to friends the other day & there’s is supposed to be a big horsey people gathering but we worked out it is just a horse feed promotion thing. We won’t get sucked into it usually these products are not organic & not really as beneficial as they make out & so expensive. I love your comment good weight & poop doesn’t really give you the full picture. Have a wonderful weekend ahead.

    Liked by 1 person

    1. Thank you again! If money allowed I would have stayed in college a lot longer than four years. Luckyily they allow us alum limited access to the databases so I can still do some research on my own. I absolutely love to read up on new information and translate it for people so we can all enjoy how exciting research can be.

      Liked by 1 person

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