Effect of uterine and vaginal bacteriomes on fertility in postpartum beef cows

Infertility in beef and dairy cattle costs millions of dollars each year to the animal agriculture industry. The microbiome of the reproductive tract has been indicated to have an effect on pregnancy establishment and maintenance in humans, however the bovine reproductive microbiome and its effect on fertility is not well understood. The objective of the current study is to evaluate bacterial communities of the uterus and vagina of postpartum beef cows undergoing estrous synchronization to determine differences in cows who will become pregnant and those who fail to conceive to fixed time artificial insemination (FTAI). Thirty Angus cows at an average of 82 days postpartum were subjected to a 7 Day Co-Synch protocol with a pre-synchronization step 21 days prior to FTAI (d -21). Uterine and vaginal flushes were collected at each day of the protocol for pH detection and bacterial DNA extraction and sequencing targeting the V1-V3 hypervariable region of the 16S rRNA gene. Pregnancy diagnosis occurred on d 30 by transrectal ultrasound where ten non-pregnant and ten pregnant cows were selected for sequencing. Results indicated a significant decrease between d -9 and d -2 in the number of bacterial species in the uterus of pregnant and non-pregnant cows (P < 0.0001). Many significant differences in relative abundance of bacteria phyla and genera were detected between pregnant and non-pregnant cows and over the duration of the protocol. Many bacteria, such as the common pathogenic bacteria Cornyebacterium, had relative abundances greater than 1% at d -2 in the uterus of non-pregnant cows, but present in less than 1% in the uterus of pregnant cows (P < 0.05). When evaluating pH, uterine pH was lower than vaginal pH on average. Although not significant, uterine pH decreased in pregnant cows and increased in non-pregnant cows through the duration of the estrous synchronization protocol. In conclusion, our data suggests the bovine reproductive tract microbiome fluctuates over time and differences in bacterial species abundances may affect reproductive outcomes.