Persistent breeding-induced endometritis in mares: effects on early pregnancy endocrinology and innovative therapies

Many mares are susceptible to persistent breeding-induced endometritis (PBIE), an important cause of reduced fertility. The exact influence of PBIE on the production of progesterone is not yet fully understood. The first study focused on measuring progesterone concentrations and luteal tissue area in non-bred mares, those bred becoming pregnant, and those bred but failing to become pregnant. It involved 52 cycles from 14 mares, monitored up to 10 days post-ovulation. Progesterone concentrations and luteal tissue area varied with time (P=0.001) but not with group (P>0.05). The second study aimed to determine the associations of the duration of estrus endometrial edema and the presence of intrauterine fluid accumulation with progesterone secretions. A total of 174 estrous cycles from 128 mares were included. Post breeding uterine fluid accumulation was associated with a decrease (p=0.009) in progesterone concentrations, and longer periods of uterine edema were associated with higher (p=0.0003) progesterone concentrations at the first pregnancy diagnosis (15 days post-ovulation). Focusing on the treatment of PBIE in mares, traditionally multiple methods are involved, often including unnecessary use of broad-spectrum antibiotics. Recognizing the urgent need for new treatments, the last part of this PhD thesis explored the use of platelet lysate (PL, derived from freeze-thawing platelets after concentration) as an innovative therapy for mares susceptible to PBIE. A total of 14 mares underwent an untreated cycle (Ctr) followed by a treated cycle with PL. A significant decrease (P<0.05) was observed on cytology score (PL 1.3±0.1 vs Ctr 2.0±0.1), fluid accumulation (PL 79.5±30.1 mm2 vs Ctr 342.7±52.9 mm2) and edema score (PL 1.8±0.2 vs Ctr 2.3±0.2) in treated mares. Pregnancy rate in PL-treated cycles (3/12) and control cycles (2/14), were not significantly different (P>0.05), but the difference was clinically interesting. Therefore, the treatment with PL in mares susceptible to PMIE reduced the inflammatory response after breeding.