Interestingly, bovine endometrial epithelial cells increase production of inflammatory cytokines in response to sperm via the TLR2/TLR4 pathways [42], which may explain why we observed changes in cows following uterine infection that were all inseminated, opposed to observation made in healthy cows where cycling cows that were never inseminated were used as the baseline comparison for pregnancy [17–19]. Here, TLR4 is linked to endometritis.