Development of an intrauterine infection model in the postpartum dairy cow

To develop an intrauterine infection model for <i>Trueperella pyogenes</i> in postpartum dairy cows and to assess the effect of this infection on the degree of intrauterine inflammation and concentrations of progesterone in serum. The oestrous cycles of 36 healthy, non-pregnant, postpartum dairy cows were synchronised. They were then treated by intrauterine infusion of 0.5 g cephapirin before being blocked by age and randomly assigned to treatment with intrauterine infusion of saline (n = 18), 10⁷ (n = 9) or 10⁹ (n = 9) cfu of <i>T. pyogenes</i>, approximately 4 days after the expected time of ovulation (Day 0). Prior to intrauterine infusion on Day 0 and again on Days 3, 7, 10, and 15, cytobrush samples were collected from the uterus of each cow for microbiology and assessment of the percentage of polymorphonuclear neutrophils (PMN%). Blood samples were collected on the same days for measurement of concentrations of progesterone in serum, and uterine lumen diameter was assessed daily using transrectal ultrasonography. <i>Trueperella pyogenes</i> was isolated from 5/18 (28%), 7/9 (78%) and 8/9 (89%) cows infused with saline, 10⁷ or 10⁹ cfu of <i>T. pyogenes</i>, respectively (p 0.05), whereas it was higher on Days 7 and 10 than Day 0 in the 10⁷ cfu group, and higher on Days 3 and 10 than Day 0 in the 10⁹ cfu group (p 2 mm was higher in cows infused with 10⁷ (29.3 (95% CI = 14.5–44.2)%) or 10⁹ cfu (19.2 (95% CI = 7.0–31.5)%) than in control cows (3.1 (95% CI = 0.1–6.0)%) (p 7 cfu (2.01 (SE 0.19) ng/mL) than cows infused with 10⁹ cfu (1.01 (SE 0.27) ng/mL), with the control group intermediate (1.41 (SE 0.19) ng/mL) (p = 0.03). Infusion of 10⁷ or 10⁹ cfu of <i>T. pyogenes</i> resulted in the establishment of intrauterine infection in 83% of cows. Infection resulted in increased uterine lumen diameter, and an inflammatory response, i.e. elevated PMN%. This intrauterine infection model may be useful for future research on, for example, the pathogenesis of intrauterine infection in postpartum dairy cows.