Lactulose drives a reversible reduction and qualitative modulation of the faecal microbiota diversity in healthy dogs

Hepatic encephalopathy (HE) is a syndrome of neurologic dysfunctionand an important contributor to patient morbidity in dogs with liver diseases. The prebiotic lactulose, a nonabsorbable synthetic disaccharide, is a frequently employed treatment for canine HE, yet within completely understood mechanisms of action. In humans, HE is linked with dysbiosis, which has been associated with worsened morbidity and mortality. The impact of lactulose in ameliorating this HE-associated dysbiosis or general modulation of the intestinal microbiotais controversial. It is unknown if dysbiosis is present in canine HE and the influence of lactulose on the intestinal microbiota has also not been assessed in dogs. The aims of this study were therefore to examine the changes in faecal microbiota composition before, during and after lactulose treatment in healthy dogs.
A total of 21 healthy privately owned dogs were enrolled in a prospective cohort study (12 females, 9 males, median age 5 years [range2-10]) with 18 completing the study fully. Faecal samples were collected weekly, while dogs were either on their usual diet (week 1), followed by a standardised commercial diet (weeks 2-9), with added oral lactulose (0.5 mL/kg every 12 hours) in weeks 6-7. Faecal bacterial DNA extraction was followed by PCR amplification of the V4 region of the 16S rRNA gene. Illumina standard 16S library prep and sequencing was performed on the MiSeq platform and data analysed using the QIIME2™ pipeline.
After 2 weeks of lactulose treatment (week 7) significantly lower faecal microbiota richness/diversity was observed based on the alpha diversity metrics: observed operational taxonomic units, Shannon/ Chao1indexes and Pielou's evenness. Beta diversity, based on Uni Frac distances, was also significantly different in week 7 compared to weeks 1, 5 and 9. At the bacterial phylum and family levels, week 7 was associated with a significant increase of Firmicutes and Actinobacteria (Veillo-nellaceae and Bifidobacteriaceae), and decrease of Bacteroidetes and Fusobacteria (Bacteroidaceae, Fusobacteriaceae, Ruminococcaceae and Alcaligenaceae), when compared to weeks 5 and 9. Finally, an extrapolated cirrhosis dysbiosis ratio (CDR) was calculated, for which lower values are associated with dysbiosis and linked with worse outcomes in humans. CDR was increased in week 7 compared to weeks 1, 5 and 9. In conclusion, lactulose induced a reversible qualitative and quantitative change of the faecal microbiota in healthy dogs, possibly explaining its potential benefit in the management of HE.