The Gut Is the First Domino

An Essay on Leaky Gut, Chronic Disease, and Why Your Pet’s Illnesses Start in the Intestines

Inflammatory bowel disease in cats was virtually nonexistent twenty years ago. Today it is one of the most frequent diagnoses.¹

That observation comes from Donald Hamilton, DVM, a veterinarian with decades of clinical experience. It is not a statistical abstraction. It describes a disease that went from rare to epidemic within a single generation of animals. Hamilton reports the same trajectory in dogs, where IBD has appeared over the past five to ten years and was, prior to that, essentially unknown.²

A disease does not go from nonexistent to epidemic in twenty years because of genetics. Genetics don’t move that fast. Something in the environment changed, and it changed the gut first.

Hamilton is not alone in this observation. Messonnier identifies idiopathic inflammatory bowel disease as the most common gastrointestinal diagnosis in dogs and cats, with most doctors suspecting some type of allergy — an immune disease.³ Pitcairn, whose fifty-year career has spanned the entire arc of this epidemic, writes that immune disorders are now among the most common conditions veterinarians are asked to treat.⁴ They were not, when he began practice. The timeline is compressed enough to fit within a single veterinarian’s career.

The veterinary literature — written by practitioners trained in conventional medicine who arrived at these conclusions through clinical observation — points to the intestinal lining as the central point of failure behind this epidemic. The allergies, the autoimmune conditions, the thyroid disorders, the skin eruptions, the ear infections, the behavioural problems — these are not separate diseases with separate causes. They are downstream consequences of a single upstream event: the breakdown of the intestinal barrier.

The mechanism is not obscure. It is described, in varying degrees of detail, across every major holistic veterinary text. What follows is an attempt to lay it out clearly — not as theory, but as the convergent finding of veterinarians working independently, observing the same patterns, and arriving at the same conclusion.

A note on language: This essay uses conventional immunological terminology — "immune system," "antibodies," "autoimmune response" — because the veterinary sources it draws from use that language. These practitioners observed real biological phenomena and described them using the framework they were trained in. I have written elsewhere about why I consider the "immune system" concept itself to be a construct that obscures more than it reveals (see [What is the "Immune System"?]). The core argument of this essay — that the internal condition of the gut determines health outcomes — is a terrain argument, even when dressed in conventional vocabulary. The clinical observations are sound. The interpretive framework they're wrapped in is not the one I would choose. I use it here because it remains the language most readers, and most veterinarians, understand.

What is the “Immune System”?

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The Wall

The intestinal lining is a selective barrier. Its job is to allow digested nutrients into the bloodstream while keeping everything else out — bacteria, toxins, undigested food particles, and the vast microbial ecosystem that inhabits the gut.

The scale of that ecosystem is worth pausing on. The actual number of microorganisms living in the intestinal tract outnumbers all the cells in the body.⁵ These are not parasites. They are essential partners in digestion, nutrient synthesis, pathogen control, and immune regulation. The intestinal bacteria produce vitamin K and many of the B vitamins. They compete with harmful organisms for space and resources. They produce chemicals that inhibit the growth of pathogenic bacteria.⁶ A healthy gut is not sterile. It is a carefully balanced ecology.

This selectivity depends on the integrity of the mucosal lining and on a functioning immune presence within it. The gut wall is not passive. It is the body’s largest immune organ. Lymphocytes — immune cells — line the intestinal tract in enormous numbers, producing an antibody called IgA (Immunoglobulin A) that serves as the first line of immune defence in the digestive system. IgA neutralises foreign material at the mucosal surface before it can reach the bloodstream. It is, as veterinarian Alfred Plechner describes it, the law and order of the intestinal tract.⁷

When this barrier is functioning, food is broken down into basic nutrient components, absorbed through the intestinal wall, and distributed to the body. Bacteria stay where they belong. Toxins are neutralised. The immune system remains calm.

When this barrier fails, the consequences cascade through every system in the body.

The condition is called intestinal hyperpermeability, or leaky gut syndrome. The mechanism, as described by Shawn Messonnier, DVM: whole proteins leak through the wall of the digestive tract due to a hyperpermeable condition and enter the blood, causing allergic reactions. These reactions may include food allergies, arthritis, autoimmune diseases, impaired nutrient absorption, and chemical sensitivities.⁸

That list — food allergies, arthritis, autoimmune disease — is not a list of possibilities. It is a description of the caseload that fills veterinary clinics every day. Messonnier goes further: it is theorised that many chronic diseases, often treated for years with various conventional medications, may in fact result from leaky gut syndrome.⁹

Richard Pitcairn, DVM, PhD — whose doctoral work was in veterinary immunology — describes the same mechanism from the immunological side. When the intestinal lining is damaged, large undigested foreign protein molecules pass directly into the tissues surrounding the intestines. The immune system overreacts to these proteins as though an invasion were taking place.¹⁰ The body mounts an immune response against food. Against its own tissues. Against things it should tolerate.

This is the mechanism behind autoimmunity. Not a mysterious malfunction. A predictable response to a barrier that has been breached.

The damage radiates outward from the gut. Plechner traces the pathway: intestinal turmoil permits allergens and impurities to enter the bloodstream. Mast cells react by secreting histamine, which makes the walls of tiny blood vessels more permeable. Blood seeps into adjacent tissue, causing chemical reactions, irritation, inflammation, and itchiness.¹¹ This is why the most visible symptom of a gut problem is often the skin — the frenzied scratching, the chronic ear infections, the hot spots. The skin is the external spokesman for internal affairs.¹²

What Breaks the Wall

The conventional veterinary approach treats each chronic condition as a separate problem requiring a separate drug. The holistic literature identifies something different: multiple simultaneous assaults converging on a single target.

Three forces, in particular, are documented across the source texts as drivers of intestinal barrier breakdown. They are not competing explanations. They are compounding ones.

The Food

A puppy or kitten born today will likely eat commercial kibble from weaning until death. That kibble will contain corn and soy — in North America, more than 80 percent of which is genetically modified and sprayed with glyphosate.¹³ It will contain grain fractions, rendered by-products, and chemical preservatives. It will be heated to temperatures that destroy enzymes and alter protein structures. Every meal, every day, for a lifetime.

Glyphosate has become a prime suspect in intestinal barrier breakdown. Research from MIT has identified that because gut bacteria are technically plants, they are being killed by glyphosate residues in food. This alters the microbial ecosystem of the intestines, allowing colonisation by harmful organisms and damaging the intestinal lining itself.¹⁴ Pitcairn connects this directly to the rise in celiac disease, gluten intolerance, food allergies, autoimmune diseases, and inflammatory bowel disease — all increasing since the 1990s, when GM crops were introduced.¹⁵

The GM crops themselves carry additional concerns. Italian government-sponsored research found that mice fed Bt corn showed elevated IgE and IgG antibodies, elevated cytokines, and elevated T cells — markers typically associated with allergies, arthritis, inflammatory bowel disease, multiple sclerosis, and cancer. There were also signs of liver and kidney toxicity.¹⁶ Animal studies found increased inflammation in the stomachs of pigs fed GM versus non-GM feed. The intestines of most US pigs are now too thin to be used in making sausage casings.¹⁷

Several generations of American dogs and cats have been raised on kibble full of GM corn and soy, plus by-products of farm animals fed the same way. They have been, as Pitcairn puts it, inadvertent test animals.¹⁸

But the dietary assault extends beyond glyphosate and GMOs. The basic composition of commercial pet food — high in processed carbohydrates, sugars, and grain fractions — feeds the wrong organisms in the gut. Pitcairn notes that excess dietary sugar feeds damaging species like Candida, which in turn damage the intestinal lining further.¹⁹ Messonnier documents that Candida albicans, a common yeast, has been observed to enter the bloodstream from the intestinal tract and may cause chronic allergies. Overgrowth of this yeast occurs in pets with chronic intestinal disease, producing toxins that worsen leaky gut syndrome.²⁰

The dietary damage is continuous and cumulative. It does not arrive as a single event but as a permanent condition — a gut lining under siege at every meal.

The Drugs

When a pet develops symptoms — diarrhoea, vomiting, skin infections, ear infections — the conventional veterinary response frequently involves antibiotics. Often for weeks or months. Sometimes for years.

Antibiotics do not distinguish between pathogenic bacteria and beneficial ones. They destroy both. The consequences for the gut are severe and well-documented across the veterinary literature.

Messonnier identifies the specific factors that disrupt the normal flora of the bowel: surgery, medications including steroids and NSAIDs, antibiotics — especially when used long-term — illness, and dietary factors.²¹ The disruption is not subtle. Antibiotics devastate the population of good bacteria, and the loss of these beneficial microorganisms can cause vomiting, diarrhoea, liver problems, immune imbalances, and allergies.²²

Ron Carsten, DVM, describes what he sees clinically: when he treats animals with a history of multiple antibiotic treatments and digestive problems, he routinely finds that probiotic supplementation produces major improvement — improvement he attributes to the restoration of bacterial balance. These cases frequently involve cats who had antibiotic courses as kittens and subsequently developed inefficient or compromised digestive systems.²³ The damage inflicted in kittenhood persists for years — sometimes for life — because the microbial ecosystem, once destroyed, does not spontaneously restore itself.

The irony is structural. The pet develops intestinal symptoms — partly because of diet, partly because of a compromised gut lining. The veterinarian prescribes antibiotics. The antibiotics further destroy the beneficial bacteria that protect the intestinal lining. The gut becomes more permeable. More symptoms appear. More drugs are prescribed. Donna Starita Mehan, DVM, states it directly: conventional veterinary treatments can often be a cause of yeast infections. If you bring in an animal with itchy skin or a bowel upset, a veterinarian will often prescribe an antibiotic. This will further upset the digestive tract, and then you have new problems.²⁴ In her practice, she reports, yeast infections are more often involved in digestive disorders than any other cause, including parasites.²⁵

NSAIDs and corticosteroids compound the damage through their own mechanisms. Messonnier documents that Candida overgrowth occurs in pets undergoing chronic antibiotic or NSAID therapy, and that the organisms produce toxins that cause leaky gut syndrome. The increased intestinal permeability then allows greater absorption of the microorganisms and their toxins, causing further harm.²⁶ Patients with inflammatory bowel disease already have a cell turnover rate in the intestinal mucosa at least three times higher than healthy patients. These patients cannot make N-acetylglucosamine, a deficiency that leads to further intestinal damage and increased permeability.²⁷

This is a feedback loop, not a treatment path. Each pharmaceutical intervention weakens the very system that needs to be strengthened. The antibiotics kill the beneficial bacteria. The dying bacteria leave space for Candida. The Candida produces toxins that damage the gut wall. The damaged gut wall lets more allergens into the bloodstream. The allergens produce symptoms. The symptoms prompt more drugs. The drugs damage the gut further.

The Vaccines

Hamilton’s observation about IBD going from nonexistent to epidemic is not made in isolation. He connects it directly to vaccination — specifically, to the introduction of parvovirus and coronavirus vaccines.

His clinical experience: IBD commonly arises within a month or two after vaccination for one of these viruses. He has been seeing inflammatory bowel disease in dogs over the past five to ten years, coincident with the introduction of parvovirus vaccination programs some thirty years after the equivalent vaccination programs began in cats — where IBD was already epidemic.²⁸

The mechanism is immunological. Pitcairn, drawing on his PhD training in veterinary immunology, explains it: vaccines insert foreign proteins from pathogens directly into the bloodstream, bypassing the layered tier of normal body defences. This triggers an inflammatory overreaction that becomes chronic. The vaccine mix contains cellular components from the tissue cultures the viruses were grown on, and the immune system confuses these with its own normal body tissues. This results in the formation of chronic immune disorders and allergies.²⁹

Purdue University research confirmed the mechanism. Vaccinated dogs, compared with unvaccinated controls, produced autoantibodies — against their own body constituents including DNA and collagen.³⁰ A separate study found that cats vaccinated with products grown on cat kidney cells made antibodies against their own kidney cells.³¹

Catherine O’Driscoll’s survey data adds statistical weight: 56.9 percent of dogs with colitis developed the condition within three months of vaccination. She notes that this finding may help current research seeking to establish the vaccine-colitis-irritable bowel link.³²

The connection to the gut is specific. Hamilton explains that whatever affinity an organism has for an organ system will surface with vaccine reactions. Parvovirus causes severe damage to the intestinal tract. A vaccine made from parvovirus, Hamilton observes, produces chronic versions of the same damage — which manifests as inflammatory bowel disease.³³

This is not a separate problem from the dietary and pharmaceutical assaults on the gut. It is the same target, hit from a different direction.

The Convergence

No single factor is solely responsible. That is precisely the point.

A puppy is taken from its mother at eight weeks. It is stressed — new environment, new people, new food. Within days, it receives its first multi-valent vaccine: parvovirus, distemper, adenovirus, parainfluenza, sometimes more, injected simultaneously. The immune system, still developing, is overwhelmed. Pitcairn notes that more than one virus or microorganism injected at one time confuses and overwhelms the recognition function of the immune system, causing errors.³⁴

The puppy develops a mild reaction — loose stool, lethargy, perhaps a low-grade fever. The veterinarian prescribes antibiotics as a precaution. The antibiotics destroy the developing population of beneficial gut bacteria, which were already under strain from the stress of rehoming and the abrupt dietary transition to commercial kibble.

The kibble, meanwhile, is doing its own work. Corn and soy derivatives — genetically modified, carrying glyphosate residues — feed the wrong organisms in the gut. Candida and other opportunistic yeasts begin to colonise the intestinal tract. The beneficial bacteria that would normally keep them in check have been depleted by the antibiotics.

Three weeks later, the puppy receives its second round of vaccines. The immune system, already primed for error by the first round, mounts a more aggressive autoimmune response. The intestinal lining — already compromised by dysbiosis, already inflamed by dietary irritants — becomes hyperpermeable.

Whole proteins begin crossing the intestinal wall. The immune system attacks them as invaders. Food allergies appear. Skin eruptions follow. Ear infections become chronic. The veterinarian prescribes more antibiotics, perhaps a course of steroids.

The puppy is six months old. It has been through two or three rounds of vaccines, two or more courses of antibiotics, and has eaten nothing but processed commercial food since weaning. Its gut lining is compromised. Its microbiome is devastated. Its immune system is misfiring. Every subsequent intervention — more vaccines, more antibiotics, more NSAIDs — drives the damage deeper.

This is not a hypothetical scenario. It is the standard timeline for the majority of puppies and kittens in the developed world. The convergence of these three forces — dietary damage, pharmaceutical destruction of the microbiome, and vaccine-induced immune disruption — all targeting the same organ, explains why chronic disease in companion animals has exploded within a single generation.

The Endocrine-Immune Connection

There is a deeper layer to this story, and it begins with a question: why do some animals’ guts fail under these pressures while others hold?

Alfred Plechner, DVM, spent over twenty years investigating this question. His clinical research, conducted across hundreds of autopsies and thousands of patients, identified a specific endocrine-immune defect that he believes explains the vulnerability.

The mechanism centres on cortisol — a hormone produced in the middle layer of the adrenal cortex. Cortisol regulates the activity of lymphocytes, the immune cells that produce antibodies including IgA.³⁵ Cortisol is itself regulated by ACTH, a hormone from the pituitary gland. The two exist in a feedback loop: when cortisol is adequate, ACTH production slows. When cortisol is deficient, ACTH production increases.

In hundreds of sick animals, Plechner found cortisol levels that were inadequate — below normal. The adrenal cortices themselves were visibly smaller than normal, with grossly underdeveloped tissue under the microscope, regardless of the animal’s age.³⁶

The consequences of cortisol deficiency cascade through the endocrine and immune systems. Without adequate cortisol, ACTH is not shut off. Uncontrolled ACTH stimulates excessive production of adrenal estrogen. Excess estrogen binds and inactivates thyroid hormone, suppresses lymphocyte and antibody activity, and neutralises what little cortisol the system is producing.³⁷

The result, as Plechner describes it, is a domino effect. Defective cortisol leads to excess ACTH, which leads to excess estrogen, which ties up remaining cortisol and thyroid hormone, which produces abnormal lymphocyte and antibody activity.³⁸

For the gut specifically, the cortisol defect relates to a breakdown of intestinal wall protection, where IgA is being over- or underproduced. This allows chemical toxins, insulting food molecules, and harmful germs to readily gain entry into the bloodstream.³⁹

Plechner connects this to the explosion of breed-specific and cross-breed disease: years of inbreeding and line breeding for cosmetic standards have damaged the adrenal cortex genetically. The defect is passed from purebreds to purebreds, from purebreds to mixed breeds, and from mixed breeds to other mixed breeds.⁴⁰

Ann Martin, in her investigation of the pet food industry, corroborates Plechner’s clinical findings on malabsorption: approximately 70 percent of his patients cannot digest food properly. The problem is frequently due to the endocrine-immune defect that causes a destabilisation of IgA in the gut, leading to subsequent inflammation in the intestinal lining.⁴¹

This explains a phenomenon that frustrates veterinarians and pet owners alike: why some animals seem to react to everything. It is not that they are unlucky. It is that their intestinal wall protection was compromised before the dietary, pharmaceutical, and vaccine-related assaults even began. The three converging forces break through a wall that, in genetically compromised animals, was already thin.

What Conventional Veterinary Medicine Sees

A veterinarian examining a dog with chronic skin allergies, recurring ear infections, and intermittent diarrhoea will typically see three separate problems requiring three separate treatments. An antihistamine for the skin. An antibiotic for the ears. A prescription diet for the gut.

The holistic veterinary literature sees one problem: a breached intestinal barrier producing systemic immune dysfunction that manifests differently depending on the individual animal’s vulnerabilities.

Pitcairn, reflecting on fifty years of practice, describes the shift: these immune disorders are among the most common conditions we are asked to treat — involving arthritis, cystitis, dog ear yeast infections, thyroid disorders, epilepsy, skin itching, and so on. This problem has greatly increased since he first entered practice.⁴²

Hamilton frames it in terms of disease classification. Acute diseases are caused by infectious organisms and can theoretically be prevented by vaccination. Chronic diseases are caused by immune system malfunction — either overactivity or deficiency. The conditions filling veterinary clinics today — allergies, lupus, autoimmune haemolytic anaemia, inflammatory bowel disease, thyroid disorders — are chronic diseases. They are autoimmune in nature. And they are rapidly increasing in number.⁴³

The conventional response to these conditions is suppressive. Steroids suppress the immune reaction. Antibiotics suppress the bacterial symptoms. NSAIDs suppress the inflammation. Each intervention addresses the visible symptom while leaving the underlying cause — the compromised intestinal barrier — untouched. Or worse: each intervention further damages the gut, ensuring the condition returns, often in a more severe form.

Hamilton observed this pattern throughout his career. The dog with a flea allergy needs steroids each spring. The dose that worked last year proves inadequate, and must be increased. Even during the symptom-free winter, the allergy has worsened. The patient must therefore be sicker than the year before, despite the body’s continual attempts to heal.⁴⁴ Broadening his observation to all diseases, Hamilton saw that conventional medicine rarely cured anything. It merely bought time.⁴⁵

The pattern is consistent because the mechanism is consistent. Suppress the symptom, leave the gut compromised, watch the disease progress. The profession treats the trees and cannot see the forest — or, perhaps more accurately, treats the branches while the roots rot.

The Study That Will Never Be Funded

The mechanism described in this essay — intestinal hyperpermeability as the common pathway through which diet, pharmaceuticals, and vaccination produce chronic disease — is not fringe speculation. It is described, with varying emphasis and terminology, by every major holistic veterinary text: Pitcairn, Messonnier, Hamilton, Plechner, Schwartz, Zucker and the many veterinarians they interview. These are not amateurs. Pitcairn holds a PhD in veterinary immunology. Hamilton is a conventionally trained DVM who spent decades in practice before arriving at his conclusions. Plechner conducted clinical research across thousands of patients over twenty-plus years and published his findings in peer-reviewed veterinary journals. Messonnier’s text is used as a reference by integrative practitioners across the country.

The clinical observations converge. Practitioners trained in different modalities — homeopathy, Chinese medicine, orthomolecular medicine, conventional integrative practice — independently identify the gut as the primary site where health breaks down and chronic disease begins. They use different language. They propose different treatments. But they agree on where the problem starts.

What does not exist is the definitive study. No one has funded a controlled trial tracking intestinal permeability in vaccinated versus unvaccinated, kibble-fed versus fresh-fed animals over their lifetimes. No one has measured IgA levels, microbiome diversity, and intestinal barrier integrity across these variables simultaneously, following the animals from birth to death.

The absence of this study is not evidence that the mechanism is wrong. It is evidence that the study would threaten the three industries that profit from the current arrangement: pet food manufacturers, pharmaceutical companies, and the vaccination-dependent veterinary business model. A study confirming that the convergence of commercial diet, routine antibiotics, and annual vaccination protocols damages the intestinal lining and produces the chronic diseases that generate the majority of veterinary revenue — that study will not be funded by anyone with the resources to fund it. This is the streetlight effect in operation: questions that threaten powerful interests go unexamined, and the absence of evidence is presented as evidence of absence.

Messonnier acknowledges the gap directly: while controlled studies are lacking, holistic doctors often attempt gastrointestinal detoxification for pets with many diseases in an attempt to heal a leaky gut that may be contributing to clinical signs or disease.⁴⁶ Hamilton writes with more certainty about what he has observed: IBD arising within months of vaccination, in patterns too consistent to be coincidence.⁴⁷ Plechner’s endocrine-immune mechanism, reported in veterinary journals in 1976, 1978, and 1979, opened a new therapeutic avenue for every veterinarian who investigated it — and was never taken up by the profession at large.⁴⁸ It fell between the cracks, as Plechner himself noted, of adrenal conditions the profession was more familiar with.⁴⁹

The mechanism is understood. The clinical observations are consistent across decades and across modalities. The three assaults on the intestinal barrier are documented. The downstream diseases are the ones that fill every veterinary clinic in every developed country.

The document that would connect all of this definitively — the longitudinal, controlled, multi-variable study of gut integrity in companion animals — is publicly absent. The mechanism it would confirm is hiding in plain sight, scattered across the veterinary literature in the books that practitioners write when they can no longer reconcile what they observe with what they were taught. Those books are consistent with each other. They describe the same patterns. They identify the same cause.

The gut is the first domino. Everything that follows — the allergies, the autoimmunity, the organ disease, the behavioural disturbances, the slow decline that owners are told is just ageing — falls from that initial breach. The breach is not mysterious. It is produced, reliably and predictably, by the standard protocols of modern pet care.

Hamilton documented it. Pitcairn explained the immunology. Plechner traced the endocrine cascade. Messonnier catalogued the treatments. O’Driscoll quantified the vaccine connection. Their books sit on shelves, read mostly by the already converted. The veterinary profession at large continues to treat the downstream symptoms — the skin, the ears, the joints, the thyroid — with the same drugs that damage the gut further.

The question is not whether the mechanism is real. The question is who benefits from pretending it isn’t.

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References

1. Hamilton, D. Homeopathic Care for Cats and Dogs: Small Doses for Small Animals. North Atlantic Books, 1999. p. 374.

2. Hamilton, pp. 374–375.

3. Messonnier, S. Natural Health Bible for Dogs & Cats. Three Rivers Press, 2001. Inflammatory Bowel Disease section.

4. Pitcairn, R. & Pitcairn, S. Dr. Pitcairn’s Complete Guide to Natural Health for Dogs & Cats. 4th ed. Rodale, 2017. Autoimmune diseases discussion.

5. Pitcairn, Chapter 3 (Leaky Gut and Declining Health section).

6. Messonnier, Probiotics/Prebiotics section.

7. Plechner, A. & Zucker, M. Pet Allergies: Remedies for an Epidemic. Very Healthy, 1986/2023. pp. 25–26.

8. Messonnier, Leaky Gut Syndrome section.

9. Messonnier, Leaky Gut Syndrome section.

10. Pitcairn, Food allergies discussion.

11. Plechner & Zucker, pp. 26–27.

12. Plechner & Zucker, p. 27.

13. Pitcairn, Chapter 3 (GMO discussion). Citing that more than 80 percent of North American food contains GMOs.

14. Pitcairn, Chapter 3 (Leaky Gut and Declining Health section). Referencing MIT research on glyphosate and gut bacteria.

15. Pitcairn, Chapter 3.

16. Pitcairn, Chapter 3. Citing Italian government-sponsored research on Bt corn and immune responses.

17. Pitcairn, Chapter 3. Citing animal studies on GM feed and pig intestinal inflammation.

18. Pitcairn, Chapter 3.

19. Pitcairn, Food allergies discussion.

20. Messonnier, Leaky Gut Syndrome section.

21. Messonnier, Probiotics/Prebiotics section.

22. Zucker, M. The Veterinarians’ Guide to Natural Remedies for Dogs/Cats. Three Rivers Press, 1999. Diarrhoea and Vomiting section.

23. Carsten, R. In Zucker, Veterinarians’ Guide (Cats edition). Using Probiotics section.

24. Mehan, D.S. In Zucker, Veterinarians’ Guide (Dogs edition). Yeast infections discussion.

25. Mehan, in Zucker, Yeast infections discussion.

26. Messonnier, Leaky Gut Syndrome section.

27. Messonnier, Glucosamine section (IBD and N-acetylglucosamine discussion).

28. Hamilton, pp. 374–375.

29. Pitcairn, Chapter 16 (Vaccines: Friend or Foe?).

30. Pitcairn, Chapter 16. Citing Purdue University School of Veterinary Medicine studies.

31. Pitcairn, Chapter 16.

32. O’Driscoll, C. What Vets Don’t Tell You About Vaccines. 2nd ed. Abbeywood Publishing, 1998. Survey results, p. 312.

33. Hamilton, pp. 373–375.

34. Pitcairn, Chapter 16.

35. Plechner & Zucker, pp. 60–61.

36. Plechner & Zucker, p. 62.

37. Plechner & Zucker, pp. 63–65.

38. Plechner & Zucker, pp. 66–67.

39. Plechner & Zucker, p. 67.

40. Plechner & Zucker, pp. 61–62.

41. Martin, A.N. Food Pets Die For. NewSage Press, 2008. Malabsorption section, citing Plechner.

42. Pitcairn, Autoimmune diseases discussion.

43. Hamilton, pp. 365–366.

44. Hamilton, pp. 25–26.

45. Hamilton, p. 26.

46. Messonnier, Leaky Gut Syndrome section.

47. Hamilton, pp. 374–375.

48. Plechner & Zucker, p. 68.

49. Plechner & Zucker, p. 68.