Reproductive microbiome and cytokine profiles associated with fertility outcomes of postpartum beef cows

Differing bacterial abundances are associated with pregnancy establishment in postpartum beef cows. Immunological factors can also be a determining factor in pregnancy status. Lay Summary Efficiently producing cattle to feed a growing population can come with many challenges. A few challenges occur soon after a cow has given birth, and subsequent reproductive performance can be impacted. Bacteria within the reproductive tract can trigger an immune response and together play a role in affecting fertility in cows. The objectives of this experiment were to distinguish the commensal vs. harmful bacteria that reside in the reproductive tract and to characterize the immune response in beef cattle via uterine and vaginal flushes. The results demonstrated that bacteria within the reproductive tract of beef cattle changes before breeding. The current study also suggests that changes in immune response before breeding can be associated with fertility outcomes. Additional research may be worthwhile to evaluate management tactics to positively shift bacteria within the reproductive tract and reduce inflammatory immune responses to improve fertility and increase reproductive efficiency. Future research is necessary to identify the causes of bacterial shifts and how it relates to pregnancy establishment. Shifts from commensal bacteria (for example, Lactobacillus in the phylum Firmicutes) within the reproductive tract have been associated with changes in local reproductive immune responses and decreased fertility in humans. The objective of this study was to characterize the microbiome and cytokine concentrations before artificial insemination (AI) in vaginal and uterine flushes from postpartum beef cows. Twenty Bos indicus-influenced beef cows (approximately 60 d postpartum and free of reproductive, health, or physical issues) were enrolled. The B. indicus prostaglandin (PG) 5-d + controlled intervaginal drug-releasing estrus synchronization protocol was initiated on day -8 of the study with timed AI on d0. Blood samples were collected on days -3, -1, and 28 via coccygeal venipuncture. Vaginal and uterine flushes were collected on days -3 and -1. Based on days 28 pregnancy status determined by transrectal ultrasonography, cows were identified as either Open (n = 13) or Pregnant (n = 7). Bacterial community analyses were conducted targeting the V4 hypervariable region of the 16S rRNA gene. Cytokine analyses were performed using the RayBiotech Quantibody Bovine Cytokine Array Q1 and MyBioSource ELISA kits per the manufacturer's instructions. Statistical analyses for bacteria relative abundance were conducted using PROC NPAR1WAY and for cytokine concentrations using PROC GLM in SAS 9.4. Uterine concentrations of interferon & gamma;, interleukin (IL)1 & alpha;, and IL21 were greater in Open than in Pregnant cows (P < 0.05). Regardless of pregnancy status, uterine IL13 increased from days -3 to -1 (9.76 vs. 39.48 & PLUSMN; 9.28 pg/mL, respectively; P < 0.05). Uterine relative abundance of the phylum Firmicutes decreased from days -3 to -1 in Open cows (60.4% & PLUSMN; 0.9% vs. 48.5% & PLUSMN; 3.2%; P = 0.004). In Open cows, the genus Blautia decreased in relative abundance within the uterus from days -3 to -1 (2.1% & PLUSMN; 0.2% vs. 0.9% & PLUSMN; 0.1%; P = 0.002). Uterine relative abundance of the phylum Tenericutes increased from days -3 to -1 in Pregnant cows (1.0% & PLUSMN; 0.1% vs. 7.6% & PLUSMN; 4.1%; P = 0.002). In Pregnant cows, the genus Ureaplasma tended to increase within the uterus from days -3 to -1 (0.08% & PLUSMN; 0.06% vs. 7.3% & PLUSMN; 4.1%; P = 0.054). These findings suggest a distinct difference in the reproductive microbiome and cytokine profiles before AI for resulting Open vs. Pregnant cows.