What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Fecal Transplant (FMT): Science and Veterinary Use

Name: Fecal Transplant (FMT): Science and Veterinary Use
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

A fecal transplant, formally called fecal microbiota transplantation or FMT, is the transfer of screened stool from a healthy donor into the gastrointestinal tract of a patient to rebuild a disrupted gut microbial community. In human medicine it is the best-established treatment for recurrent Clostridioides difficile infection, and in veterinary medicine it is used as an adjunct for acute and chronic enteric disease in dogs, with growing but preliminary evidence in cats and horses.

This article explains what fecal transplants are, how they work at the level of bile acids and short-chain fatty acids, how donors are screened, how fresh and frozen preparations differ, and how the human and veterinary versions of the procedure compare. It is written for US pet owners, veterinary students, and technicians who want a source-grounded picture rather than marketing claims.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

What Are Fecal Transplants and Why the Gut Microbiome Matters

Diagram comparing gut microbiota of obese and lean mice after transplant — Mice receiving obese human microbiota gain more fat, illustrating why donor microbiome composition matters in FMT. Image: Muséum d'histoire naturelle de Toulouse, CC BY-SA 3.0, via Wikimedia Commons.

The gut microbiome is the collective community of bacteria, archaea, fungi, viruses, and their metabolites living in the intestinal tract. A healthy canine colon contains hundreds of bacterial taxa working in a fermentation-based economy. These microbes break down dietary fiber and host-derived substrates into short-chain fatty acids (SCFAs), chiefly acetate, propionate, and butyrate. Butyrate is the primary fuel for colonocytes, the cells lining the colon, and SCFAs help regulate luminal pH, water absorption, and local immune tone [1].

When that community is disrupted, a state called dysbiosis, the consequences reach beyond digestion. Dysbiosis has been documented in dogs with acute and chronic digestive disease and in diseases of other organ systems [2]. A qPCR-based canine Dysbiosis Index (DI) quantifies this shift, with higher values indicating a more abnormal microbiota. Dogs with acute diarrhea show significantly increased DI, decreased alpha-diversity (the number and evenness of species within a sample), and altered beta-diversity (how different one sample's community is from another) compared with healthy dogs [3].

FMT works by reintroducing a functional community rather than by killing a specific pathogen. The transferred material contains not only live commensal bacteria but also bacteriophages, fungi, bacterial metabolites, bile acids, and immunoglobulin A (IgA) from the donor [1]. Each of these components can influence the recipient's gut environment.

How FMT Works: Mechanisms Beyond Simple Bacterial Transfer

Restoring Microbial Diversity

The most consistent measurable effect of FMT is a rise in microbial diversity. In a pilot study of dogs with acute hemorrhagic diarrhea syndrome (AHDS), the Shannon diversity index was significantly lower in affected dogs than in healthy donors at admission. After FMT, diversity rose from admission to discharge in recipients and became significantly higher than in sham-treated controls, eventually matching donor levels [4]. A separate study comparing FMT enema with oral metronidazole in dogs with acute diarrhea found that FMT restored microbial diversity and beta-diversity to a state similar to healthy controls by day 28, while metronidazole-treated dogs remained significantly different from healthy controls [3].

Bile Acid Conversion

Bile acids are synthesized in the liver, conjugated, secreted into the small intestine to aid fat digestion, and then modified by colonic bacteria. Primary bile acids are deconjugated and converted to secondary bile acids by specific microbial enzymes. This conversion matters because secondary bile acids help inhibit pathogens such as C. difficile and shape the overall community.

In a study of dogs with refractory chronic enteropathy treated with repeated FMT, long-lasting responders had a significantly higher baseline percentage of secondary unconjugated fecal bile acids (65 percent) than nonresponders and short-lasting responders combined (30 percent). The dysbiosis index also decreased significantly in long-lasting responders by the third FMT but not in the other group [5]. This suggests that a recipient's baseline bile acid profile may influence whether FMT takes hold.

Short-Chain Fatty Acid Effects

SCFAs are the end products of bacterial fermentation and serve as an energy source for colonocytes, regulators of intestinal pH, and signaling molecules for the immune system. A case report of a dog with chronic diarrhea after parvovirus infection documented an increase in SCFA metabolites after oral lyophilized FMT capsules, alongside complete resolution of diarrhea and a two-kilogram weight gain [6]. The AHDS pilot study also hypothesized that FMT would increase SCFA-producing microbial communities [4].

Immune Modulation and Engraftment

Donor bacteria do not always colonize the recipient permanently. In a proof-of-concept study of oral FMT in dogs with tylosin-responsive enteropathy, an average of 30.4 percent of donor bacterial strains engrafted into recipients [7]. Engraftment is partial and variable, which helps explain why clinical responses can be inconsistent. Beyond direct colonization, FMT may modulate host immunity through IgA, bacterial metabolites, and interactions with gut-associated lymphoid tissue [1]. Proposed mechanisms also include gut-brain axis signaling, which is the basis for investigating FMT in canine cognitive dysfunction and epilepsy-related behavioral comorbidities [8].

The following flowchart shows the core decision path from a patient with suspected dysbiosis through donor screening to administration and follow-up.

flowchart TD
    A[Patient with suspected dysbiosis] --> B[Confirm diagnosis and rule out other causes]
    B --> C[Identify suitable healthy donor]
    C --> D[Screen donor stool and blood]
    D --> E{Screening results normal}
    E -->|No| C
    E -->|Yes| F[Prepare fresh or frozen inoculum]
    F --> G[Choose route by species and condition]
    G --> H[Administer FMT]
    H --> I[Monitor clinical scores and adverse events]
    I --> J[Assess response and adjust plan]

Human Indications: Recurrent C. difficile Infection

In people, FMT is recognized as the best treatment modality for recurrent Clostridioides difficile infection (CDI), a condition in which antibiotic treatment repeatedly fails and the patient cycles through relapse [2]. The logic is straightforward. C. difficile flourishes when broad-spectrum antibiotics wipe out the normal colonic community. Restoring that community, including bile-acid-converting bacteria that produce secondary bile acids inhibitory to C. difficile, breaks the relapse cycle.

Human FMT is also investigated in other conditions associated with an abnormal gut microbiome, but the strength of evidence varies widely by indication. The recurrent CDI indication is the anchor. Veterinary FMT has borrowed the same conceptual framework but applies it to different diseases and different species.

Veterinary Indications: Dogs, Cats, and Horses

Chronic Enteropathy in Dogs

Chronic enteropathy (CE) is the most studied canine FMT indication. Observational studies frequently report reduced disease activity scores after FMT, while small randomized trials have shown mixed results [8]. In a prospective study of 39 dogs with refractory CE treated with two to three rectal FMTs over one month, 28 of 39 dogs responded. Responders had significantly decreased CIBDAI (Canine Inflammatory Bowel Disease Activity Index) scores at one month that remained stable at six months in long-lasting responders. Corticosteroid tapering was achieved in 13 responders, and mild adverse events were noted in four dogs [5].

A separate study of 14 dogs with CE refractory or incompletely responsive to dietary management used daily owner-completed CIBDAI monitoring after a single retention enema FMT. Clinician-assigned scores showed a significant overall effect of time, but no pairwise comparison remained significant after correction. Daily monitoring showed a significant nonlinear pattern, with the derivative significantly negative between Days 2 and 5, meaning owners reported improvement in that early window [9].

A randomized, double-blind, placebo-controlled trial of oral FMT in dogs with tylosin-responsive enteropathy found that relapse occurred in 2 of 7 FMT-treated dogs (28.6 percent) versus 3 of 6 placebo-treated dogs (50 percent). The dysbiosis index decreased over time in both groups with no treatment effect. Faecalibacterium species increased with higher posttreatment values in the FMT group, and Peptacetobacter hiranonis increased over time without between-group differences [10]. A related proof-of-concept study reported that 5 of 7 FMT dogs and 3 of 6 placebo dogs did not relapse during the four-week trial, with no statistically significant difference between groups [7].

A single rectal FMT study in seven dogs with CE found median CCECAI decreased from 8 before FMT to 3 within one week and 1 by Day 30, with an average duration of response of approximately 10 weeks. Recipient microbiota composition or diversity did not change over time in that study, and significant variation in donor microbiota composition was observed across different donations [11]. This last point is a practical warning: not every donor sample is equivalent.

Case reports describe dramatic individual responses. A 10-year-old Toy Poodle with lymphocytic-plasmacytic duodenitis received periodic long-term FMT by rectal enema from a healthy Golden Retriever donor, and post-FMT fecal microbiome diversity resembled the donor's [12]. A Shiba dog with non-responsive enteropathy received a single endoscopic FMT into the cecum and colon during chlorambucil treatment, with recovery of clinical signs, clinicopathological abnormalities, and dysbiosis [13]. A dog with chronic diarrhea after parvovirus infection resolved completely after oral lyophilized FMT capsules [6]. Case reports generate hypotheses but do not establish efficacy.

Acute Hemorrhagic Diarrhea Syndrome in Dogs

AHDS is an acute, severe bloody diarrhea syndrome in dogs, associated in some studies with Clostridioides perfringens overgrowth and toxin-mediated mucosal necrosis. In the pilot study of one and seven dogs with AHDS, there were no significant differences in median AHDS clinical scores between FMT recipients and sham-treated controls at admission or discharge. Diversity increased in FMT recipients from admission to discharge and was significantly higher than in sham-treated controls, but by 30 days diversity did not differ among recipients, controls, and donors [4]. The microbiome signal was real. The clinical signal was not statistically significant in that small study.

Canine Parvovirus Enteritis

The strongest controlled canine signal for FMT comes from parvoviral enteritis [8]. In a randomized clinical trial of 66 puppies with parvovirus infection, puppies receiving standard treatment plus FMT (10 g of feces from a healthy dog diluted in 10 mL of saline, administered rectally 6 to 12 hours post-admission) had faster resolution of diarrhea and shorter hospitalization (median 3 days versus 6 days) compared with standard treatment alone. Mortality was 21.2 percent in the FMT group versus 36.4 percent in the standard group, but this difference was not statistically significant [14].

A more recent double-blinded, placebo-controlled trial of 27 dogs with parvovirus used a spectrum-of-care regimen: a single FMT enema followed by 14 days of oral lyophilized FMT capsules. Interim analysis found that placebo-treated dogs had excessive study withdrawals due to worsening clinical status (37.5 percent versus 0 percent in the FMT group), leading to ethical discontinuation of the placebo arm. FMT-treated dogs had significantly reduced hospitalization length and required fewer medications [15].

Feline and Equine Use

Feline data support short-term tolerability and measurable microbiome activity, but clinical efficacy remains preliminary. The first controlled feline chronic enteropathy trial showed no significant improvement in dysbiosis index or clinical activity scores compared with controls [8]. Equine colitis is a recognized target for FMT in horses, and the enema route is used because of the size and anatomy of the equine colon, but controlled efficacy data in horses remain limited compared with the canine parvovirus and human CDI evidence base.

Emerging Extra-Intestinal Applications

Investigations are extending beyond the gut. A pilot study of nine dogs with drug-resistant epilepsy and behavioral comorbidities used three FMTs two weeks apart from a donor dog that was seizure-free on phenobarbital, with behavioral and cognitive assessments at three and six months [16]. A pilot evaluation of a single oral FMT in 12 dogs with atopic dermatitis found significant decreases in CADESI-04 scores from a median of 16.5 at day 0 to 8 at day 56, and PVAS scores from 3 to 1, alongside changes in fecal microbiota composition [17]. A study of oral FMT capsules in 11 dogs with suspected canine cognitive dysfunction found that cognition improved in 4 of 6 dogs with complete data and worsened in 2, with increased microbiome richness and diversity in 4 of 6 dogs [18]. These are early signals, not established treatments.

Donor Screening: The Critical Safety Step

Donor screening is the single most important safety measure in FMT. A donor that carries a pathogen or a multidrug-resistant organism can transmit it to a recipient whose gut barrier and immune defenses are already compromised.

Donor Selection Criteria

A suitable donor is a healthy animal with no history of gastrointestinal disease, no chronic illness, no recent antibiotic exposure, and no immunosuppressive treatment. The donor should be up to date on vaccinations and parasite prevention, and should be fed a consistent diet so the microbiota is stable. In the canine studies, donors were healthy dogs with unremarkable behavior and no gastrointestinal signs [4][16]. In one case report, the donor was a 4-year-old neutered male Golden Retriever weighing 32.8 kg [12].

Exclusion criteria include any history of immunosuppression, current or recent antibiotic treatment, and any condition that could alter the fecal microbiome. Antibiotic-treated animals are excluded because their microbiota is disrupted and may harbor resistant organisms. Immunosuppressed animals are excluded because they may shed pathogens at higher rates or carry organisms that are harmless to them but dangerous to a recipient.

Fecal Pathogen PCR Panel

A fecal pathogen PCR panel tests donor stool for common enteric pathogens. In veterinary practice this typically includes Salmonella species, Campylobacter species, Clostridioides perfringens toxin genes, Clostridioides difficile toxin genes, canine parvovirus, canine distemper virus, and Giardia species. A donor with a positive result on any pathogen target is excluded. The exact panel composition varies by laboratory, and the clinician should use a validated panel appropriate to the species and region.

Parasite Examination

Direct fecal examination and fecal flotation screen for intestinal parasites including Giardia, Cryptosporidium, Toxocara, Ancylostoma, Trichuris, and Cystoisospora. A donor with any detectable parasite is excluded. Some protocols also include a fecal culture for Salmonella and Campylobacter to complement PCR.

Blood Screening

Donor blood screening typically includes a complete blood count, serum biochemistry, and testing for vector-borne and infectious diseases appropriate to the region, such as heartworm antigen, Ehrlichia, Anaplasma, and Borrelia. The goal is to confirm the donor is systemically healthy, not just free of enteric pathogens.

Repeat Screening

Because a donor's microbiome and pathogen status can change over time, repeat screening is recommended at intervals during an active donation period. The variation in donor microbiota composition across different donations observed in one canine study underscores why a single screening event may not capture the full risk profile [11].

Fresh Versus Frozen Preparations: Viability and Practical Tradeoffs

FMT material can be prepared fresh or frozen, and the two differ in microbial viability and logistics.

Fresh preparations are used immediately after collection and processing. They preserve the full complement of live bacteria, metabolites, and IgA, but they require the donor and recipient to be available at the same time and place. The canine parvovirus trial used fresh feces diluted in saline and administered rectally within hours of collection [14].

Frozen preparations allow banking and scheduled administration. Glycerol is commonly added as a cryoprotectant. In a study of dogs with CE, samples stored with 10 percent glycerol showed a difference in microbiota composition compared with samples stored without glycerol, meaning the cryoprotectant itself can shift the community profile [11]. Freezing inevitably reduces the viability of some anaerobic bacteria, and the clinical consequences of that loss are not fully characterized.

Lyophilized (freeze-dried) capsules are a third option. They are shelf-stable, easy to administer orally, and have been used in canine parvovirus, chronic enteropathy after parvovirus, cognitive dysfunction, and atopic dermatitis studies [6][18][17][15]. Lyophilization reduces water content and improves storage stability, but it also stresses bacterial membranes, and viability varies by taxon.

The practical rule is that fresh material offers the highest theoretical viability, frozen material offers the best logistics, and lyophilized capsules offer the best owner convenience. No head-to-head trial has established that one preparation is clinically superior to another for any canine indication.

Administration Routes by Species

The route of administration depends on species anatomy, the target segment of gut, and the clinical setting.

Rectal enema is the most common veterinary route. In dogs, a retention enema delivers material to the distal colon and rectum. The parvovirus trial used rectal administration of 10 g feces in 10 mL saline [14]. The CE studies used retention enemas [9][11][5]. Enema administration is relatively simple, does not require anesthesia, and allows the material to be retained for a period to promote contact with the colonic mucosa. The main limitation is that the proximal small intestine is not directly reached.

Nasogastric or nasoesophageal tube administration is used when the upper gastrointestinal tract is the target or when enema retention is not feasible. In horses with colitis, nasogastric tubing is used because the equine colon is large and the enema route cannot reliably deliver material to the proximal colon. In small animals, nasogastric administration requires a tube and may be used in hospitalized patients.

Oral capsules are used for conscious, swallowing patients. Lyophilized FMT capsules have been used in dogs for parvovirus, chronic enteropathy, cognitive dysfunction, and atopic dermatitis [18][6][17][15]. Oral administration passes through the stomach, where acid may reduce viability of some organisms, but capsules can be enteric-coated to improve delivery to the small intestine.

Endoscopic administration into the cecum and colon has been described in a dog with non-responsive enteropathy, allowing direct deposition of material at the target site [13]. This route requires anesthesia and specialized equipment but offers precise delivery.

Colonoscopy is the standard human route for lower gastrointestinal delivery, while upper gastrointestinal routes including nasogastric tube, gastroscopy, and oral capsules are also used in people.

Human Versus Veterinary FMT: A Comparison Table

Feature	Human FMT	Veterinary FMT
Primary established indication	Recurrent Clostridioides difficile infection [2]	Canine parvoviral enteritis (strongest controlled signal) [8]
Other common indications	Investigational for ulcerative colitis, metabolic and neurological conditions	Chronic enteropathy, acute hemorrhagic diarrhea syndrome, acute diarrhea, emerging extra-intestinal uses [4][11][5][16][17]
Donor source	Screened human donors, often from a stool bank	Healthy dogs, cats, or horses, often the owner's own healthy pet or a known healthy animal [4][12]
Donor screening	Stool pathogen PCR, parasite exam, blood screening for infectious diseases, exclusion of immunosuppressed or antibiotic-treated donors	Fecal pathogen PCR panel, parasite exam, blood screening, exclusion of immunosuppressed or antibiotic-treated donors
Route of administration	Colonoscopy, nasogastric tube, oral capsules	Rectal enema, nasogastric tube, oral capsules, endoscopic delivery [9][14][15][13]
Preparation forms	Fresh, frozen, lyophilized capsules	Fresh, frozen with glycerol, lyophilized capsules [6][14][11]
Regulatory status	Regulated as a biologic or tissue product in many jurisdictions	Not uniformly regulated, practiced as a clinical procedure
Evidence strength	High for recurrent CDI, variable for other indications	Strong for parvovirus, mixed for chronic enteropathy, preliminary for most other uses [10][14][8][15]

Step-by-Step Protocol Overview

The following sequence reflects the general structure of published veterinary FMT protocols. Specific volumes, concentrations, and retention times vary by clinician and species, and no drug doses are provided here.

Confirm the diagnosis and rule out other causes of the clinical signs. FMT is not a substitute for diagnostic workup.
Identify a candidate donor. A healthy animal with no gastrointestinal disease, no recent antibiotics, and no immunosuppression is preferred.
Screen the donor. Collect stool for a fecal pathogen PCR panel and parasite examination. Collect blood for a complete blood count, serum biochemistry, and species-appropriate infectious disease testing.
Exclude the donor if any screening test is positive or if the donor has been on antibiotics or immunosuppressive drugs.
Prepare the inoculum. Fresh material is processed and used within hours. Frozen material is mixed with a cryoprotectant such as 10 percent glycerol and stored at minus 80 degrees Celsius. Lyophilized material is encapsulated.
Choose the route. Rectal enema for distal colonic delivery, nasogastric tube for upper gastrointestinal delivery, oral capsules for conscious patients, or endoscopy for targeted delivery.
Administer the FMT. For enema, the material is instilled and retained for a period to allow contact with the mucosa.
Monitor the patient. Record clinical scores, fecal consistency, and any adverse events. Mild adverse events such as transient vomiting or diarrhea have been reported [5].
Assess response. Re-evaluate clinical activity scores and, where available, fecal dysbiosis markers at one week, one month, and three months.
Repeat if needed. Some protocols use two to three FMTs over one month, and repeated administration has been associated with response in refractory CE [5].

Clinical Relevance, Limitations and Common Mistakes

FMT is not a guaranteed cure, and the evidence base in veterinary medicine is smaller and more heterogeneous than in human medicine. The most common mistake is treating FMT as a first-line therapy for any diarrhea. Acute diarrhea in dogs often resolves with supportive care, and FMT should be reserved for cases where the clinician has a specific rationale, such as parvoviral enteritis, refractory chronic enteropathy, or recurrent C. difficile infection.

A second mistake is using an unscreened donor. The convenience of a household pet as a donor does not remove the need for pathogen screening. Transmission of a multidrug-resistant organism to an already compromised recipient is a serious risk.

A third mistake is assuming that a clinical response proves the mechanism. In the AHDS pilot study, diversity improved significantly while clinical scores did not differ significantly from controls [4]. In the CE study of a single rectal FMT, clinical scores improved while recipient microbiota composition and diversity did not change [11]. Clinical response and microbiome change do not always move together.

A fourth mistake is ignoring donor variability. Significant variation in donor microbiota composition across donations has been documented [11], and donor-recipient strain engraftment is partial, averaging about 30 percent in one study [7].

A fifth mistake is overstating the evidence for extra-intestinal uses. The cognitive dysfunction, epilepsy, and atopic dermatitis studies are pilot or single-arm investigations with small sample sizes [18][16][17]. They justify further research, not routine clinical use.

Individual animals respond differently, and any decision to use FMT should be made with a veterinarian who can assess the specific case, screen the donor, and monitor for adverse events.

Frequently Asked Questions

What is a fecal transplant?

A fecal transplant is the transfer of screened stool from a healthy donor into the gastrointestinal tract of a patient to restore a disrupted gut microbial community.

Is FMT the same as a probiotic?

No. Probiotics contain a small number of defined bacterial strains, while FMT transfers a complex community including bacteria, bacteriophages, fungi, metabolites, bile acids, and IgA [1].

What is the main human use of FMT?

Recurrent Clostridioides difficile infection is the best-established human indication [2].

Which veterinary condition has the strongest FMT evidence?

Canine parvoviral enteritis has the strongest controlled canine signal, with faster diarrhea resolution and shorter hospitalization in treated puppies [14][8].

Can FMT help dogs with chronic enteropathy?

Observational studies often report reduced disease activity scores, but small randomized trials have shown mixed results [10][8][5].

How are FMT donors screened?

Donors are screened with a fecal pathogen PCR panel, parasite examination, and blood testing, and are excluded if immunosuppressed or recently treated with antibiotics.

Does freezing FMT reduce its effectiveness?

Freezing reduces the viability of some anaerobic bacteria, and adding glycerol as a cryoprotectant can shift the microbiota composition [11]. No head-to-head trial has proven one preparation superior.

Are there risks to FMT?

Yes. The main risk is transmission of a pathogen or multidrug-resistant organism from an inadequately screened donor. Mild adverse events such as transient gastrointestinal signs have been reported [5].