Identification of the gut microbiota biomarkers associated with heat cycle and failure to enter oestrus in gilts.

Failed puberty is one of the main reasons for eliminating gilts from production herds. This is often caused by disorders of sex hormones. An increasing number of studies have suggested that the gut microbiota may regulate sex hormones and vice versa. Whether the gut microbiota is involved in the failure of oestrus in gilts remains unknown. We used 16S rRNA gene sequencing, network-based microbiota analysis and prediction of functional capacity from 16S rRNA gene sequences to explore the shifts in the gut microbiota throughout a heat cycle in 22 eight-month-old gilts. We found that a module of co-occurrence networks composed of Sphaerochaeta and Treponema, co-occurred with oestrus during a heat cycle. The mcode score of this module reflecting the stability and importance in the network achieved the highest value at the oestrus stage. We then identified bacterial biosignatures associated with the failure to show puberty in 163 gilts. Prevotella, Treponema, Faecalibacterium, Oribacterium, Succinivibrio and Anaerovibrio were enriched in gilts showing normal heat cycles, while Lachnospiraceae, Ruminococcus, Coprococcus and Oscillospira had higher abundance in gilts failing to show puberty. Prediction of functional capacity of the gut microbiome identified a lesser abundance of the pathway 'retinol metabolism' in gilts that failed to undergo puberty. This pathway was also significantly associated with those bacterial taxa involved in failed puberty identified in this study (P < 0.05). This result suggests that the changed gut bacteria might result in a disorder of retinol metabolism, and this may be an explanation for the failure to enter oestrus.