191 Variation in the vaginal microbiota of mares during the oestrus cycle

The reproductive health of mares may be reflected in their vaginal microbiota, but few studies have described the changes occurring during the oestrus cycle. Information about the normal microbiota in healthy mares is needed as an aid to diagnosis reproductive problems or pathology. The purpose of this study was to characterise changes in the normal vaginal microbiota during the oestrous cycle of mares. Swab samples were taken from the vagina of 13 mares on a stud farm near Uppsala, Sweden, during the first cycle of the season using a double-guarded swab. The area of the ventral vagina adjacent to the cervical fornix was sampled. Swabs were taken on four occasions, representing different stages of the cycle, and thus differing in hormonal influence. Day 0 was taken 24 h preceding ovulation, when progesterone would have been at its lowest level; Day 3 with a developing corpus luteum (CL) and increasing progesterone levels; Day 7 with a fully developed CL and maximum progesterone influence; and Day 14 with a regressing CL and declining progesterone level. The swabs were direct cultured on four different agar plates: blood agar, lactose purple agar, MacConkey agar, and Baird-Parker agar, which were incubated in aerobic atmosphere at 37°C for 24 + 24 h. Furthermore, one blood agar plate was incubated in an anaerobic atmosphere at 37°C for 24 + 24 h and a De Man, Rosa, and Sharpe agar (MRS-agar) in an anaerobic atmosphere at 25°C for five days. Bacterial colonies differing in macromorphology were re-cultured to obtain pure cultures for identification by MALDI-TOF MS. Overall, 372 isolates from 24 bacteria species were identified. The most frequently isolated bacterium was Escherichia coli (40%), with Streptococcus zooepidemicus being the second most abundant (11.3%), and the anaerobe Fusobacterium varium being the third most abundant (2.4%). One mare had E. coli as the dominant bacterium throughout the cycle; in three mares, E. coli was isolated on all occasions. However, the presence or absence of a specific bacterium differed among mares, as did the number of isolates, making it impossible to identify a specific pattern during the oestrus cycle. There was a tendency for the same flora to be present on Day 14 as on Day 0. A significant positive correlation was observed between the presence of E. coli and S. zooepidemicus; r = 0.53 (P = 0.0002). The most common bacterium in the vagina of these healthy mares was E. coli. Although different bacteria were present on different days during the oestrus cycle, it was difficult to detect a particular pattern in bacterial species and the stage of the oestrus cycle of the mare, which may be due to the small number of individuals sampled. The pattern most frequently seen was that the microbiota on Day 14 most closely resembled the microbiota on Day 0, suggesting that the regressing CL may have favoured the establishment of certain bacteria. Two species, E. coli and S. zooepidemicus, were correlated, suggesting a possible interaction between these species.

This research was supported by Agria and the Swedish Veterinary Association, Stockholm.