Why chronic complaints rarely have only one cause:
the intestinal axes
Skin, behavior, joints, bladder, lungs: they seem to be different problems. But they often have the same origin. Find out how the gut affects your dog or cat’s entire body through a network of connections.
By Stefan Veenstra DVM
You may know it. Your dog has been scratching for months. Or your cat has bladder problems over and over again. Either one of them is more anxious than before, stiffer when getting up, or has a restless stomach that just won’t go away.
The strange thing is: many of these animals have several things going on at the same time. Skin and behavior. Abdomen and joints. Blow and sneeze attacks. That seems like a coincidence, but it rarely is.
In recent years, science has shown more and more clearly that the intestine is the central organ from which all these complaints are controlled. Not the only cause, but the most common common denominator. This works through what researchers call the intestinal axes : connecting routes between the intestine and the rest of the body.
What are intestinal ashes?
An intestinal axis is a connecting route between the intestine and another organ or system in the body. Not in one direction, but in two directions. The intestine influences that organ, and that organ in turn also influences the intestine.
These connections run through different channels. Sometimes through the blood, through inflammatory substances that reach the entire circulation. Sometimes via nerve pathways, directly from intestine to brain and back. Sometimes through hormones. And sometimes via the bacteria in the intestine itself, which produce substances that have an effect far outside the intestine.
It is always about what goes wrong when the intestine is disturbed: if the microbiome is out of balance (dysbiosis), if the intestinal wall becomes too permeable (leaky gut), or if too many harmful substances flow from the intestine into the body. This disrupts communication through all those axes at the same time. And that is exactly why in many chronically ill animals you do not see one problem, but several problems in several places at the same time.
The common cause
All gut axes have a common problem as a starting point: a disturbed gut microbiome. If the intestinal bacteria are confused, it has three direct consequences that together form the basis for chronic complaints.
Less good substances
The good bacteria produce fewer protective substances (such as butyrate) that keep the intestinal wall strong and inhibit inflammation.
Leaky gut wall
The connections between the intestinal cells become looser. Bacterial residues and waste products leak into the circulation and put the immune system on alert.
Dormant inflammation
The immune system is constantly a little “on”. Not an acute infection, but a persistent low-grade inflammation that puts a strain on the whole body.
Through the intestinal axes, this dormant inflammation spreads to organs and systems that seem to have nothing to do with the intestine itself. Skin, brain, joints, kidneys, eyes: they all react to the same disturbance in the intestine.
The main intestinal axes in dogs and cats
Gut and skin
This is one of the most visible compounds in dogs. A disturbed gut microbiome increases the amount of histamine in the blood and moves the immune system toward allergic reactions. This makes the skin more sensitive. Inflammatory substances from the intestine also damage the skin barrier itself, making it easier for bacteria and fungi to get a grip.
Clinical picture: itching, atopy, recurrent skin infections, hot spots, seborrhoea, poor response to antihistamines.
Gut and brain
About 90% of the serotonin in the body is not made in the brain, but in the gut, and is directly controlled by the gut bacteria. Via the vagus nerve, a nerve pathway from intestine to brainstem, and via the blood, the intestine continuously sends signals to the brain that influence behavior, sleep and stress responses. Stress also works the other way around: tension increases the permeability of the intestinal wall and aggravates dysbiosis.
Clinical picture: anxiety, hyperactivity, aggression, excessive licking, sleep problems, cognitive decline in older animals.
Gut and immune system
Approximately 70 to 80 percent of all immune cells are located in and around the intestines. The intestine is therefore the largest immune organ of the body. When the microbiome is disrupted, the immune balance becomes unbalanced: the body reacts too strongly to things that are normally not a problem (food, environmental factors) and sometimes also to its own tissues. The production of protective antibodies in the intestinal mucosa decreases, making it easier for infections to take hold.
Clinical picture: food sensitivities, IBD, recurrent infections, poor response to vaccinations, autoimmune complaints.
Intestine and liver
All venous drainage from the intestine goes directly through the portal vein to the liver. This makes the liver the first filter place for everything that enters the blood from the intestine. With dysbiosis, more harmful substances come along, causing the liver to become chronically overloaded. This is particularly relevant in cats: the notorious triaditis (simultaneous liver, intestinal and pancreatic inflammation) can largely be understood as an intestine-liver problem.
Clinical picture: elevated liver values without a clear primary source of the liver, gallbladder problems, triaditis in cats.
Bowel and joints
The joint tissue contains many receptors that respond to inflammatory substances from the blood, including the harmful substances released from a leaky gut. Long-term exposure increases inflammation in joints and accelerates cartilage breakdown. Good intestinal bacteria produce substances that inhibit cartilage breakdown. With dysbiosis, that protection is lost.
Clinical picture: osteoarthritis with disproportionate pain, immune-mediated joint inflammation, stiffness when standing up that coincides with intestinal complaints.
Bowel and bladder
The bladder has its own bacterial community that is partly fed from the intestine. Certain intestinal bacteria that overgrow in dysbiosis are exactly the bacteria that also cause bladder infections. In addition, a disturbed microbiome produces more ammonia-like substances that increase urine pH and promote crystal formation in the bladder. In cats with recurring bladder problems, the intestine is often underestimated as a cause.
Clinical picture: recurrent bladder infections, crystals, feline idiopathic cystitis (FIC), hematuria without infection.
Intestine and lungs
The intestine and lungs are part of the same mucous membrane network in the body. Protective substances produced by the good intestinal bacteria also have an effect on the mucous membranes of the respiratory tract: they reduce allergy reactions in the bronchi and inhibit mast cell activity. With dysbiosis, that protection is lost and the airways become more sensitive to stimuli.
Clinical picture: feline asthma, chronic cough, recurrent bronchitis, increased sensitivity to environmental allergens.
Intestine and throat, nose and ears
Through the same mucous membrane network, the intestine also affects the ears, nose and throat. Chronic ear infections in dogs are remarkably often accompanied by intestinal complaints: the systemic inflammation from the intestine increases the histamine sensitivity of the ear skin and makes the environment more attractive to yeasts and bacteria. Chronic sneezing in cats is also often associated with intestinal problems.
Clinical picture: recurrent otitis that does not respond well to local treatment, chronic sneezing in cats, ceruminous overproduction.
Intestine and eyes
Inflammatory substances from the intestine can damage the small blood vessels in the retina and tear glands. In addition, certain protective substances for the eyes (such as vitamin A and specific carotenoids) depend on healthy intestinal absorption. With dysbiosis, that absorption decreases.
Clinical picture: dry eye (KCS), recurrent conjunctivitis, uveitis in systemic immune problems.
Gut and hormones
The intestinal bacteria play a direct role in hormone metabolism. Certain bacteria convert broken down sex hormones back into active forms that are reabsorbed through the intestine. A disturbed microbiome can therefore affect estrogen and testosterone levels. The thyroid gland also depends on good intestinal function: part of the thyroid hormone is converted into the active form in the intestinal wall.
Clinical picture: false pregnancy, irregular heat, hypothyroidism that does not respond well to medication, symmetrical hair loss.
Intestine and kidneys
In cats, this is one of the most clinically relevant compounds. Certain intestinal bacteria produce substances (such as indoxyl sulfate and p-cresol sulfate) that damage the kidneys when they accumulate. Normally, the kidneys clear these substances, but with reduced kidney function they accumulate. Conversely, impaired kidney function also changes the intestinal environment, which increases dysbiosis. A self-reinforcing cycle.
Clinical picture: chronic kidney disease in cats (CKD), progressive renal impairment, uremic complaints.
Gut and bones
The good gut bacteria produce substances that inhibit bone breakdown and stimulate bone building. They also increase the absorption of calcium through the intestinal wall. With dysbiosis, this protection decreases, bone breakdown increases and mineral absorption is less efficient, even with a diet that contains enough calcium on paper.
Clinical picture: accelerated osteoarthritis progression, osteoporosis in older animals with long-term intestinal complaints, slow fracture healing.
Intestine and connective tissue (fasciae)
This is a relatively new insight. The intestinal organs are directly connected to the rest of the body via fascial ligaments and fleece tissues. All muscles are covered in muscle fascia and connect multiple muscle groups with it. Research in dogs has shown that fascial lines run from pelvis through abdominal organs to diaphragm, neck and limbs. A chronically inflamed or tense intestine literally pulls mechanically on those lines. In addition, inflammatory substances from the intestine stimulate connective tissue cells to produce more collagen, which leads to hardening and stiffness. Acupuncture at certain points along those fascial lines has a demonstrable influence on the composition of the gut microbiome.
Clinical picture: generalized stiffness with no detectable joint disease, incomplete response to internal bowel treatment alone, chronic pain that runs along fascial lines.
Why this is so important in practice
The understanding of the intestinal axes changes how you look at chronic complaints. The dog that has been itching for years, the cat that keeps getting bladder infections, the animal that reacts at the slightest stress: these are rarely isolated problems that require isolated solutions.
When an animal has complaints in several places at the same time, or when complaints keep coming back after treatment, this is a signal to look at the intestine as a common denominator. Not as the sole cause of everything, but as the system that has the most influence on the rest of the body through all those axes.
Recognizable pattern
Multiple complaints at the same time or one after the other, recurring problems despite treatment, an animal that is “never quite right” on several fronts: these are the classic signs that the system as a whole is disturbed, and that the intestine as the starting point of treatment offers the best chance of improvement.
An animal with skin complaints, fear and stiffness does not need to receive three separate treatments. Recovery of the intestine improves through the axes, all three at the same time.
What can you do?
The question owners ask as soon as they understand this is always the same: how do I go about this? There are two sides to the answer. On the one hand, the biological side: restoration of the gut microbiome and the gut barrier. On the other hand, the mechanical side: ensuring that the tension built up via the fascial axes can also be released manually.
Nutrition as a basis
Fresh, minimally processed food with sufficient variety gives the intestinal bacteria what they need. Ultra-processed dry food structurally disrupts the microbiome, regardless of price or brand. Approximately 80% fresh meat and 20% mixed ground vegetables is a feasible starting point.
Phased Bowel Protocol
Restoring the microbiome works best in stages: first break down the bad biofilm and reduce inflammation, then build up the good bacteria. Putting good bacteria in a dysbiotic gut is like plants in a weed garden: they don’t survive the competition.
Manual therapy
Osteopathy, fascial release, laser therapy, or acupuncture can relieve mechanical tension along the gut-fasciae axis. In fact, acupuncture at specific points along the abdominal region has a direct demonstrable effect on the composition of the gut microbiome.
Patience and system
Recovery via the axes is not a quick intervention. The microbiome takes weeks to months to stabilize. But the good news: if it succeeds, health improves on several fronts at the same time, because the axes all respond positively.
The intestine as a control center
The intestine is not an isolated digestive organ. It is the control center of health, connected through a network of axes to every other system in your dog or cat’s body. A disturbed microbiome sends signals via all these axes at the same time that lead to complaints in places that seem to have nothing to do with the intestine.
That’s the good news: if you treat at the root, the whole system improves. Not because the intestine determines everything, but because the intestine has the most influence on everything at once.
Would you like to know more about how the NGD Care Bowel Protocol approaches this in practice? Check out the full protocol below. For a scientific in-depth study per axis, we refer to the article on StefanVeenstra.nl.
View the NGD Care Bowel Protocol and start restoring the basics
This information is educational in nature and does not replace a veterinary consultation. For a scientific substantiation of the intestinal axes with literature references, see the article on StefanVeenstra.nl.