Objectives of this experiment were to study the effect of infusing utero-pathogenic bacteria to induce endo-metrial inflammation on productive performance in early lactation and subsequent reproduction. Although endometritis is associated with perturbed reproduction, numerous factors may contribute to the observed as-sociation. It was hypothesized that induced endome-trial inflammation, resulting in localized and systemic inflammatory responses, compromises production and reproduction. Holstein cows without clinical disease and with less than 18% polymorphonuclear leukocytes (PMN) in endometrial cytology on d 31 & PLUSMN; 3 postpar-tum had their estrous cycle synchronized. Cows were blocked by parity and genomic breeding value for cow conception rate and, within block, assigned randomly to remain as untreated controls (CON; n = 37) or to receive an intrauterine infusion of 5.19 x 108 cfu Esch-erichia coli and 4.34 x 108 cfu Trueperella pyogenes during the luteal phase to induce endometrial inflam-mation (INF; n = 48). Endometrial cytology was taken on d 2 and 7 after treatment to evaluate the proportion of PMN. Rectal temperature, dry matter intake, and yields of milk and components were measured in the first 7 d after treatment. Blood serum was analyzed for concentration of haptoglobin. Leukocytes were isolated from blood on d 2 and 7 after treatment and on d 19 after artificial insemination (AI) and mRNA was quantified for a select group of genes. Cows received AI and reproduction was followed for 300 d postpartum. Bacterial infusion induced endometrial inflammation with increased proportions of PMN in the endometrial cytology on d 2 (4.4 & PLUSMN; 0.7 vs. 26.3 & PLUSMN; 2.8%) and 7 (10.9 & PLUSMN; 1.7 vs. 17.4 & PLUSMN; 2.1%) after treatment, resulting in increased mean prevalence of subclinical endometri-tis (>10% PMN; 23.3 & PLUSMN; 6.3 vs. 80.9 & PLUSMN; 5.1%). Rectal temperature did not differ between CON and INF, but the concentration of haptoglobin in serum tended to in-crease in INF compared with CON (113 & PLUSMN; 14 vs. 150 & PLUSMN; 16 & mu;g/mL). Induced endometrial inflammation reduced yields of milk (44.9 & PLUSMN; 0.8 vs. 41.6 & PLUSMN; 0.8 kg/d), protein (1.19 & PLUSMN; 0.03 vs. 1.12 & PLUSMN; 0.03 kg/d), and lactose (2.17 & PLUSMN; 0.04 vs. 2.03 & PLUSMN; 0.04 kg/d) and tended to reduce dry matter intake (20.7 & PLUSMN; 0.5 vs. 19.4 & PLUSMN; 0.6 kg/d) in the first 7 d after treatment. Indeed, the reduction in milk yield lasted 4 wk. However, treatment did not affect yields of energy-corrected milk or fat because treatment with INF increased the concentration of fat in milk (3.54 & PLUSMN; 0.10 vs. 3.84 & PLUSMN; 0.10%). Induced endometrial inflammation reduced pregnancy per AI at all insemi-nations (33.4 & PLUSMN; 5.1 vs. 21.6 & PLUSMN; 3.7%) and the hazard of pregnancy (0.61; 95% CI = 0.36-1.04), which extended the median days open by 24 d. Blood leukocytes from INF cows had increased mRNA expression of the pro -inflammatory gene IL1B on d 2 and 7 after treatment, but reduced expression of the IFN-stimulated genes ISG15 and MX2 on d 19 after AI. Induced endometrial inflammation depressed production and caused long-term negative effects on reproduction in lactating dairy cows.
