Changes in the vaginal microbiota in ewes after insertion of intravaginal sponges at different stages of the oestrous cycle

The aims of this study were to determine if the ewe' vaginal bacterial load differs according to the stage of the oestrous cycle; and thus, if the stage of the oestrous cycle when intravaginal sponges (IS) used for oestrous synchronisation are inserted influences the vaginal bacterial biota present at sponge withdrawal. During the breeding season, 45 Texel ewes were detected in oestrus and randomly allocated to one of three treatments of 15 ewes each according to the stage of the oestrous cycle when the IS were inserted. Intravaginal sponges were inserted: the day of oestrus (GOes), or 2 (GMet) or 8 (GDie) days after oestrus. Samples for bacterial analysis were collected the day of IS insertion (Day 0), at sponge withdrawal (Day 12), 24 h (Day 13) and 48 h (Day 14) after sponge withdrawal. Vaginal bacteria amount increased at sponge withdrawal in all treatment (p < 0.0001). The number of different types of colonies was greater in GMet group than in GDie at sponge insertion (p < 0.05), without difference with GOes. At sponge insertion, the presence of Staphylococcus spp. was greater in GMet than in GOe and GDi (p < 0.05); the presence of Trueperella pyogenes and Haemophilus somni was greater after sponge withdrawal than before sponge insertion (p < 0.001), but without difference between days 12, 13 and 14. Overall, we concluded that in ewes the normal vaginal bacterial load differs according to the stage of the oestrous cycle. The continuous presence of the IS homogenised the vaginal bacterial microbiota at withdrawal, with only slight and transient differences observed on day 13.