Gut microbiota of growing rabbits fed diets with different fibre and lipid contents

Fibre with its different fractions, both insoluble and soluble, is the main dietary component guaranteeing the normal functioning of the rabbit digestive physiology and gut health. Thus, the present study aimed to evaluate the effect of an increase of ADF from 18.1% to 18.8% associated with a decrease in dietary starch from 14.3% to 13.8% and an increase in dietary fat from 2.9% to 3.8% on the microbiota composition of caecal content and hard faeces. To this purpose, 576 crossbred rabbits (Hypharm, Groupe Grimaud, Roussay, France) were weaned at 31 d, assigned to the two dietary treatments, and fed the experimental diets until slaughtering (73 d of age), when hard faeces and caecal contents were sampled from 20 rabbits (10 per diet) in the afternoon (h.15:00-16:00) and analysed using a 16S rDNA multi-amplicon sequencing approach. Firstly, sequencing results showed that the microbial diversity and the bacterial community structure of the hard faeces barely differed from that of the caecal content (p > 0.05). The overall microbial composition was dominated by the phylum of Firmicutes, the Clostridia and Bacilli classes, followed by Ruminococcaceae and Lachnospiraceae as dominant families. Then, as for the diet effect, no differences in alpha and beta diversity of microbiota were detected in rabbits fed the two diets. However, twelve genera, mostly belonging to the family of Lachnospiraceae, increased (Wald test, p < 0.05) in rabbits fed the diet with the highest fibre and fat contents. Overall, these findings enhance our understanding about gut microbiota in growing rabbits and indicate that even small changes in fibre and fat of the diet may affect the composition of gut microbiota.