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Mucus: The Unsung Hero of Digestive Immunity

At DIG Labs, our mission is to help expand access to insights and data. As pet parents ourselves, one of the most frustrating aspects of caring for the health of our pets is the lack of availability of scientifically sound research when it comes to canine health. That’s why, from time to time, we’ll be writing review blogs, where we take a peer-reviewed scientific journal article, and break it down into more manageable bits of information. While you should definitely consult with your veterinarian with any questions or concerns you might have regarding your pet’s health condition, we hope that these tools will help support those conversations. Below is a summary of our latest article, which can be found here.

When thinking of the digestive system, we typically think of vomit, urine and poop. However, mucus, the unsung hero of digestive excrements, is the least understood of them all, and plays a pivotal role by:

  • Protecting our dogs from infection,
  • regulating immune response,
  • protecting the delicate intestinal lining stomach acids as they traverse the GI tract, and more.
DIG Labs Dog Health Understanding Mucus Role in Immunity

Mucus layer (yellow) protects the intestinal finger-like villi to regulate exposure to nutrients, and minimize pathogen invasion.

If you’re reading this article, chances are you’ve seen a slimy poop from your dog and are wondering – what is that coating and why is it there?

In this article, we will discuss the role of mucus – how it works, why it’s important, and when to be concerned.

Mucus – What is it?

Digestive mucus is a secretion comprising over 98% water.  Resembling a clear, shiny goop, slime, or coating, it can be found in the stomach and intestines and sometimes make its way out of the GI tract during a bowel movement.

  • In the small intestine, mucus serves as a single layer coating that protects the lining and acts as a gatekeeper – letting nutrients in and keeping germs out. For dogs, this coating is particularly important for several reasons:
    1. A dog’s digestive tract operates on a 9-hour schedule from input (food) to output (poop) – compared to humans- 24-hour schedule. This means the mucus lining must be in tip-top shape to maximize absorption of nutrients.
    2. A dog’s stomach acidity can reach as low as pH 1.5 – the equivalent of battery acid. Therefore, mucus’ role in protecting the delicate small intestine lining is even more critical given the stomach’s mega-acidity.
  • In both the stomach and large intestine, mucus comprises two layers – for the large intestine, the inner layer separates bacteria from the large intestinal lining, and the outer layer is home to the microbiota that reside there.
  • The mucus of both the small intestine and the outer layer of the large intestine can both be easily detached – this explains the slippery coating that sometimes accompanies your dog’s poop.

Mucus – Why It’s Important

Mucus can be thought of as the body’s special interpreter between the outside world and the internal environment. Mucus decides what can contact the lining of the digestive tract, and what will get “trapped.”

When you see a mucus-coated stool, it could be an indication that the body has identified an irritant or a germ, and is trying to flush it from the body. This may happen very early in an infection, or with a diet change. In this case, the body detached its mucus layer to be excreted. This is an example of the body’s first immune response kicking into gear. Good news – not all mucus-stool is a cause for a veterinarian appointment. Typically, one or two bowel movements of coated, otherwise healthy-looking poop is an indication that the mucus has done its job. Mucus that is persistent or accompanies either extremely hard or watery stool could be a sign of digestive distress, and you should consider consulting a veterinarian. Be sure to take a photo if possible.

Luckily, mucus does its job well 99.99% of the time – ensuring our dogs stay safe, healthy and protected. Sometimes, however, mucus can let some pathogens through – causing diarrhea, discomfort, bloating, and more.

Unfortunately, some pathogens can outsmart mucus. For example, E.coli can reside beneath the inner mucus layer, protecting it from clearance and excretion. These types of pathogens effectively break through the mucus barrier by cutting their way through the dense gel, and then nestle into the small intestine. This is why bacterial pathogens can be so troublesome – the body has a really hard time battling and flushing these types.

Mucus – the Ultimate Bodyguard

DIG Labs Dog Health Understanding Mucus in Dog Poop

Mucus is essentially the intestine’s ultimate bodyguard – it allows enough exposure of nutrients, vitamins and minerals to the intestinal lining to maintain optimal health, while defending against invaders. Also, mucus is providing a happy home to the microflora (the good bacteria) that aid digestion.

Because of the fleeting properties of this super-substance, our understanding of mucus still leaves much to be desired. At DIG Labs, we are developing proprietary methods to characterize mucus visually, and deploy AI-based tools to define associations between mucus and nutrition. Learn more about this and other discovery projects here.