Integrated Ultrasonographic and Progesterone Profiling for Characterization of Early Embryonic Loss in Mares

https://doi.org/10.82471/eef84-sb535

Abstract

Early embryonic death (EED) is a major cause of reproductive loss in mares during maternal recognition of pregnancy and early placentation. The present study evaluated ultrasonographic and endocrine alterations associated with EED in three multiparous mares using sequential transrectal ultrasonography and plasma progesterone profiling. Dominant follicles grew at 2–3 mm/day and reached preovulatory diameters of 42–48 mm prior to ovulation. Pregnancy was confirmed on day 12 post-ovulation by detection of a spherical embryonic vesicle (12–15 mm), which enlarged progressively to 30–36 mm by day 23 with visualization of the embryo proper. Subsequent examinations revealed embryonic vesicle regression, loss of turgidity, irregular margins, and complete disappearance of the conceptus by day 35 post-ovulation, confirming EED. Progesterone concentrations remained basal during estrus (<1 ng/mL), increased following ovulation (4–8 ng/mL), and reached 8–15 ng/mL during early pregnancy. Mares affected with EED exhibited a marked decline in progesterone concentrations after day 22 post-ovulation (2–4 ng/mL), concurrent with embryonic degeneration, luteolysis, and recurrence of estrous behavior, whereas normally pregnant mares maintained persistently elevated progesterone concentrations (>10 ng/mL). The study demonstrates that sequential ultrasonography combined with progesterone profiling is a valuable approach for early diagnosis of embryonic compromise and suggests that luteal insufficiency and failure of maternal recognition of pregnancy may contribute significantly to EED in mares.