Estradiol cypionate aided treatment for experimentally induced ascending placentitis in mares

- Exogenous estrogen improved treatment for experimentally induced placentitis by promoting the delivery of healthy foals.
- Combination of estrogen, antibiotic, anti-inflammatories resulted in no high-risk foals.
- Progestin appeared not to benefit the treatment for experimental placentitis.

The overall goal of this study was to assess the efficacy of various therapeutic combinations of estradiol cypionate (ECP, a long-acting estrogen) and altrenogest (ALT, a long-acting progestin) in addition to basic treatment for placentitis with trimethoprim-sulfamethoxazole (TMS) and flunixin meglumine (FM). Specific outcomes measured in this experiment were (i) time from induction of bacterial placentitis to delivery, and foal parameters (high-risk, survival, and birth weight); and (ii) serum steroid concentrations (progesterone, 17α-hydroxyprogesterone, 17β-estradiol, and cortisol) in response to treatment. Pregnant mares (∼300 days gestation, n = 46) were randomly assigned into healthy mares (control group, CONT, n = 8) and mares with experimentally induced ascending placentitis (n = 38). Placentitis was induced via intracervical inoculation of Streptococcus equi subspecies zooepidemicus. Thereafter, placentitis induced mares were randomly assigned into: (1) basic treatment, TMS+FM (n = 8); (2) basic treatment with ALT supplementation, TMS+FM+ALT (n = 8); (3) basic treatment with ECP supplementation, TMS+FM+ECP (n = 6); (4) basic treatment with ALT and ECP supplementation TMS+FM+ALT+ECP (n = 6); and (5) no treatment (INOC, n = 10). Treatments were started 48 h after bacterial inoculation and carried out for ten consecutive days. Blood samples were collected daily, and mares were assessed for signs of placentitis until the mare delivered, or for ten consecutive days after onset of treatment. Steroids were analyzed via RIA. Continuous data were analyzed by ANOVA, and categorical data analyzed by Fisher's exact test. Significance was set at p < 0.05. Foal survival at parturition and seven days post-delivery were similar across treated groups (66.7-100%), and to the CONT group. Similar to CONT group, mares in the TMS+FM+ECP group had no high-risk foals while mares in the other groups had higher incidences (50-75%) (p < 0.05). The inclusion of ECP in the treatments resulted in foals with body weight similar to CONT group (p > 0.05). There were no group effects or time by group interactions on concentrations of steroids assessed herein (p > 0.05). In conclusion, in addition to basic treatment TMS+FM, mares with experimentally induced ascending placentitis benefited from ECP supplementation. Conversely, ALT did not appear to make a difference in outcomes. The immunoassays used for measurements of steroid concentrations did not appear useful to assess treatment response.