Induction of endometritis after pregnancy loss during the second month of gestation in cattle and its effect on the fate of the corpus luteum

FOLCHINI N; DURAN B; RYKACZEWSKI C; CRIST A; SAAD M; CARRANZA A; MOTTA J; MOLLENKOPF D; MUSSARD M; GARCIA-GUERRA A

Ottawa

Encuentro; 56th SSR Annual Meeting; 2023

Society for the Study of Reproduction

Induced pregnancy loss (IPL), through intrauterine administration of hypertonic saline, on d35 of gestation results in conceptus demise and regression of the corpus luteum (CL) at ~8 d after IPL. Data obtained during preliminary studies, however, indicate that ~13% of cows in which pregnancy loss was induced developed uterine disease (i.e., endometritis), and the CL was maintained for ~32 d. The objective of this study, therefore, was to determine whether the occurrence of endometritis in cattle undergoing pregnancy loss during the second month of pregnancy affects CL lifespan. We hypothesized that induction of endometritis would prevent luteolysis and extend the CL lifespan in cows undergoing induced pregnancy loss. Pregnant non-lactating beef cows (n=23) at 35 days of gestation (d0) were randomly assigned into three groups: Control-pregnant (n=7), Induced pregnancy loss (IPL; n=7), and Induced pregnancy loss+Endometritis (IPL+EM; n=9). On d0, pregnancy loss was induced in cows in the IPL and IPL+EM groups through intrauterine administration of 120 ml of hypertonic saline (7.2%), while Control cows remained untreated. On d2, endometritis was induced in cows of the IPL+EM group through an intrauterine infusion of 10 ml of ~2.75×10^8 CFU/mL of E. coli MS499 and 10 ml of ~7×10^8 CFU/mL of T. pyogenes MS249. All cows were evaluated daily for rectal temperature. Transrectal ultrasonography (B-mode) was performed daily until luteolysis or the end of the experimental period at d60 (d25 after IPL) of gestation to assess CL size, embryonic/fetal viability, and characteristics of uterine contents. Plasma samples were collected twice daily and assayed for progesterone (P4) by radioimmunoassay. The onset of luteolysis was defined as the day before P4 decreased ≤50% of the average for the previous three samples. Assessment of vaginal discharge (score 0=translucent to 3=purulent) was performed on d2 to d6 and endometrial cytology was performed on d5 in the IPL+EM group. Endometrial cytological samples were evaluated for the determination of the percentage of polymorphonuclear cells (PMN). Data were analyzed using linear mixed models (SAS 9.4). The establishment of endometritis in cows of the IPL+EM group was successful as indicated by: vaginal discharge score of 3 within 24 to 72 h after bacterial infusion, percentage of PMN (32.0%±7.69) 72 h after bacterial infusion; and observation of echogenic intrauterine fluid. Rectal temperature, however, did not differ between groups (P=0.94). Pregnancy loss and luteolysis were identified in all IPL (7/7) and IPL+EM (9/9) cows, but in none of the control cows (0/7). The day of luteolysis onset was similar (P=0.35) between cows of the IPL (11.73±3.32 days; range 5.5-16) and the IPL+EM (9.41±3.01 days; range 3.5-18) groups. In conclusion, the occurrence of endometritis after induced pregnancy loss did not affect the lifespan of the CL after pregnancy loss during the second month of pregnancy in cattle.