Premature luteal regression in a pregnant mare and subsequent pregnancy maintenance with the use of oral altrenogest.
Authors: Canisso I F, Beltaire K A, Bedford-Guaus S J
Journal: Equine veterinary journal
Summary
# Editorial Summary Premature luteal regression remains poorly documented as a cause of equine pregnancy loss, despite its potential clinical significance. This case report describes a mare presenting at day 15 post ovulation with ultrasonographic evidence of endometrial oedema, an absent corpus luteum on both ovaries, and a developmentally delayed embryonic vesicle, whilst serum progesterone concentration measured only 0.67 ng/ml—well below the 2 ng/ml threshold required for pregnancy maintenance. Daily oral altrenogest supplementation was initiated immediately, with serial ultrasonography and endocrine monitoring conducted through to day 120 of gestation. Progesterone concentrations remained subthreshold (below 2 ng/ml) until day 72 of pregnancy; however, embryonic development normalised by day 25, and concurrent measurement of equine chorionic gonadotrophin and oestrone sulphate concentrations remained within expected ranges throughout, ultimately resulting in uncomplicated delivery of a healthy filly at 344 days post ovulation. This case demonstrates that oral altrenogest can effectively rescue pregnancies affected by early luteal insufficiency when initiated promptly, even when endogenous progesterone production fails to reach conventional adequacy thresholds, suggesting that supplementation may bridge the critical early gestational period until placental progesterone synthesis becomes established.
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Practical Takeaways
- •Premature luteal regression should be considered as a potential cause of early pregnancy loss in mares; routine pregnancy diagnosis at 15 days post ovulation can identify cases requiring intervention
- •Oral altrenogest is an effective therapeutic option for maintaining pregnancies complicated by luteal insufficiency, even when exogenous progesterone supplementation cannot achieve concentrations considered conventionally adequate
- •Serial ultrasound and hormonal monitoring allows confirmation of pregnancy viability and guides continuation or modification of progestin therapy in cases of suspected luteal dysfunction
Key Findings
- •A mare with premature luteal demise presented with serum progesterone of 0.67 ng/ml at 15 days post ovulation, below the threshold for adequate pregnancy maintenance
- •Daily oral altrenogest treatment maintained pregnancy despite progesterone concentration remaining below 2 ng/ml until 72 days post ovulation
- •The embryonic vesicle achieved normal development by 25 days post ovulation and resulted in delivery of a healthy filly at 344 days post ovulation
- •Concurrent measurement of equine chorionic gonadotrophin and oestrone sulphate concentrations remained within normal ranges throughout treatment