Fecal microbial transplants hastened recovery from severe diarrhea in horses

Horses who received a fecal microbial transplant showed evidence of greater normalization of their gut microbiome than a control group.
Horses who received a fecal microbial transplant showed evidence of greater normalization of their gut microbiome than a control group. Image by Manfred Richter

A watery manure concoction wouldn’t be a horse’s first choice of a drink, but it has proven effective in helping hospitalized equines overcome severe diarrhea.

The watery cocktail, given via a nasal tube into the stomach, delivered a fecal microbial transplant to the unwell horses, hastening their recovery, researchers report.

Those who received the treatment also showed evidence of greater normalization of their gut microbiome than a control group.

Normalization of the microbiome is critical to attaining gastrointestinal health. The microbiome plays an important role in digestion, development of the gut immune system through mucus production and anti-inflammatory signaling, and maintaining metabolic function.

The study team from Tufts University in Massachusetts, reporting in the open-access journal PLOS ONE, described their experiment to assess fecal microbial transplantation as a clinical treatment and regulator of fecal microbiota in hospitalized horses with colitis.

Caroline McKinney and her fellow researchers noted that colitis — inflammation of the gut lining — continues to be a leading cause of critical illness in horses, with an estimated mortality rate of 25% to 35%.

The condition is accompanied by risks for severe complications, such as laminitis, blood clotting problems and cardiovascular issues, which often require intensive care and prolonged hospital stays.

Their study centered on 22 horses with moderate to severe diarrhea, consistent with a diagnosis of colitis, who were enrolled at two referral hospitals.

Twelve horses were admitted to one hospital, and 10 to the other.

In all cases, the horses were either admitted with diarrhea, or it developed within 48 hours of admission, indicating it was related to their presenting complaint.

For all horses, their diarrhea ranged from a pudding quality to watery.

The 12 horses at the first institution all received fecal microbial transplantation on three consecutive days, while those at the other hospital received standard care without the transplants.

The transplantation involved collecting 2.5 pounds of fresh manure from a healthy donor horse and mixing it was four liters of lukewarm water. The mixture was subsequently strained and given within 15 minutes via a nasogastric tube to the recipient horse.

Manure was collected for analysis once daily for four days from the rectum in all colitis horses, before the transplant procedure for horses at the first institution, and from each manure sample used for transplants.

Fecal samples from 10 clinically healthy control horses housed at the second hospital, and 30 healthy horses located at 5 barns near the first hospital, were also obtained to characterize the regional healthy equine microbiome.

As expected, healthy horses at both locations showed a greater alpha-diversity and lower beta-diversity compared to horses with colitis.

The fecal microbiome of healthy horses clustered by location, with horses at the first institution showing a higher prevalence of Kiritimatiellaeota.

Improved manure consistency (a lower diarrhea score) was associated with a greater alpha-diversity in horses with colitis at both locations.

Fecal transplant recipients demonstrated a greater overall reduction in diarrhea score, compared to untreated horses, with a higher incidence in day-over-day improvement in diarrhea.

The horses that received the transplants delivered test results indicating greater normalization of their microbiome than those who received conventional treatment.

“In summary, this study supports the use of fecal microbial transplantation as a treatment to reduce diarrhea severity in horses with colitis and to improve microbiome diversity,” the authors concluded.

“Diarrheic horses undergoing serial fecal microbial transplantation showed a greater improvement in diarrhea severity compared to non-treated horses, and their microbiome became more phylogenetically similar to that of their donors.”

They said that while the results support the usefulness of the technique, further studies are needed to better establish treatment efficacy.

“Evidence of intestinal colonization by transplanted microbiota support the need to identify novel probiotics to accelerate re-establishment of a healthy microbiome.

“Additionally, with increasing support for the use of fecal microbial transplantation, a need to further investigate the treatment’s mechanism of action, to standardize and streamline administration protocols, develop veterinary stool banks, and explore effective storage options, may expand the accessibility of this treatment to equine practitioners.”

The study team comprised McKinney, Daniela Bedenice, Bruno Oliveira, Mary-Rose Paradis, Melissa Mazan and Giovanni Widmer, all with the Cummings School of Veterinary Medicine at Tufts University; and Ana Pacheco, with the Carlson College of Veterinary Medicine at Oregon State University.

McKinney CA, Bedenice D, Pacheco AP, Oliveira BCM, Paradis M-R, Mazan M, et al. (2021) Assessment of clinical and microbiota responses to fecal microbial transplantation in adult horses with diarrhea. PLoS ONE 16(1): e0244381. https://doi.org/10.1371/journal.pone.0244381

The study, published under a Creative Commons License, can be read here

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