Testing the Induction of Metritis in Healthy Postpartum Primiparous Cows Challenged with a Cocktail of Bacteria

SIMPLE SUMMARY: Here we tested whether a metritis induction model would induce disease in postpartum primiparous cows. Animals were challenged with an intrauterine infusion of a bacterial cocktail containing 10(3) or 10(6) cfu of Escherichia coli, Trueperella pyogenes, and Fusobacterium necrophorum. Both challenged groups were compared with a control group, infused with a sterile saline solution. The incidence of metritis did not differ among groups, but the high-dose group (10(6) cfu) had a 2.7 times greater hazard of being diagnosed with metritis when compared with the controls and had reduced milk production, which is associated with a numerical reduction in dry matter intake when compared with the other two groups. Although clinical signs of illness were detected in low-dose cows, there were no significant changes in blood concentrations of acute phase proteins, plasma cytokines, or serum metabolites after the challenge. The culture of uterine content revealed that challenging increased the bacterial counts in the vaginal discharge of Fusobacterium necrophorum, but not Escherichia coli or Trueperella pyogenes. ABSTRACT: Metritis is a postpartum uterine disease with greater incidence in primiparous than in multiparous cows. In primiparous cows, the impact on production and health is lessened, presumably due to a superior immune response. Here, we tested whether an in vivo model of clinical metritis induction developed for postpartum multiparous Holstein cows would produce similar results in primiparous cows. Thirty-six cows were randomly assigned to one of three groups and received intrauterine infusion within 24 h of parturition. The controls were infused with sterile saline; the low-dose group received a bacterial cocktail containing 10(3) cfu of Escherichia coli, Trueperella pyogenes, and Fusobacterium necrophorum; and the high-dose group were infused with 10(6) cfu of the same cocktail. Production, health traits, and the vaginal discharge culture were assessed daily, from enrollment until 14 d in milk. Clinical metritis occurred in 64% of high-dose cows, 33% of the controls, and 42% of low-dose cows, with no significant difference of incidence between groups. However, when accounting by time, high-dose cows had a 2.7 times greater hazard of metritis compared with the controls. The bacterial challenge affected milk production and dry matter intake tended to decrease. In the high-dose group, a greater growth of F. necrophorum in the selective medium was also observed, suggesting an association with metritis. Therefore, this study suggests intrauterine inoculation with 10(6) cfu of this bacterial cocktail elicits physical and clinical outcomes consistent with clinical metritis.