Faecal microbiota in horses medicated with oral doxycycline hyclate

Notice that the hyclate salt of doxycycline is used in this study. This type is better absorbed than other salts so lower doses are effective. These lower doses probably reduce doxycycline associated colitis. However even these lower doses induce changes to the microbiota and may take weeks to recover.
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Characterisation of faecal microbiota in horses medicated with oral doxycycline hyclate
Equine Vet J. 2022 Feb 24.
Authors
Ronan J J Chapuis 1 2 , Anne A M J Becker 3 , Patricia M Dowling 2 , J Scott Weese 4
Affiliations

1 Clinical Sciences, Ross University School of Veterinary Medicine, Basseterre, Saint Kitts, West Indies.
2 Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Canada.
3 Biomedical Sciences, Ross University School of Veterinary Medicine, Basseterre, Saint Kitts, West Indies.
4 Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Canada.

PMID: 35202500
DOI: 10.1111/evj.13570

Abstract

Background: Antimicrobial-associated diarrhoea is a common adverse effect of antimicrobial treatment in horses and has been reported following the administration of oral doxycycline. The administration of antimicrobials has also been associated with changes in the equine intestinal microbiota diversity yet has not been explored under doxycycline treatment.

Objectives: To describe the dynamics of the faecal microbial diversity following a 5-day oral administration of doxycycline in healthy horses with Streptococcus zooepidemicus infected tissue chambers.

Study design: Experimental prospective cohort study in a single horse group.

Methods: Seven healthy adult horses with S. zooepidemicus infected tissue chambers received oral doxycycline at 10 mg/kg q 12h for 5-days following the tissue chamber inoculation. Faeces were collected prior to the tissue chamber inoculation and until 28-days post inoculation. Faecal microbiota was characterised by high throughput sequencing of the V4 region of the 16S rRNA gene on the Illumina MiSeq sequencing platform. Bioinformatic analysis was performed with Mothur and statistical analysis were conducted on R Studio.

Results: A significant decrease in alpha diversity, characterised by a decrease of richness and diversity, and a decrease in beta diversity, characterised by changes in relative abundance, occurred after initiation of and during the administration of doxycycline. A decrease in Verrucomicrobia and increase in Firmicutes:Bacteroidetes ratio occurred following the initiation of treatment, with a return to initial Firmicutes:Bacteroidetes ratio during the treatment. It took 23 days after discontinuing the treatment for the faecal microbiota to return close to the initial state.

Main limitations: Lack of control population within the study.

Conclusions: Transitory intestinal dysbiosis occurs under oral administration of doxycycline in horses.

Keywords: Streptococcus zooepidemicus; antimicrobial; gastrointestinal microflora; horse; infection model.