Fetal Death Associated With Premature Mammary Gland Development and Lactation in a Mare Treated With Weekly Injections of Long-Acting Progesterone.
Authors: McAfoos Jessie L, Ellerbrock Robyn E, Canisso Igor F
Journal: Journal of equine veterinary science
Summary
# Editorial Summary A 14-year-old Quarter Horse mare presented at seven months gestation with unexpected udder development and milk leakage whilst receiving weekly long-acting progesterone injections for a history of subfertility, raising important questions about the safety of this treatment protocol during pregnancy. Transabdominal ultrasonography revealed fetal death in utero, prompting controlled abortion using cloprostenol; pathological examination identified a severely dilated urachus, placental mineralization, and umbilical oedema, with the fetus measuring only 53 cm crown-rump length (consistent with six months rather than seven). The premature lactation and reduced fetal development suggest that exogenous progesterone may have disrupted normal endocrine signalling, potentially triggering inappropriate mammary gland maturation and compromising placental and fetal development simultaneously. Whilst long-acting progesterone remains valuable for mares with documented luteal insufficiency or recurrent pregnancy loss, this case highlights the critical importance of carefully monitoring progesterone supplementation during the latter half of gestation and discontinuing treatment at an appropriate timepoint to avoid iatrogenic complications. Practitioners should counsel clients that continued high-dose progesterone support beyond the early months may carry reproductive risks, and emphasise the necessity of regular ultrasound surveillance in mares receiving this therapy.
Read the full abstract on PubMed
Practical Takeaways
- •Long-acting progesterone injections should be discontinued once pregnancy is confirmed, as continued treatment may trigger inappropriate lactation and adverse fetal outcomes in mares
- •Premature mammary development and galactorrhea in a pregnant mare should raise suspicion for progesterone exposure and warrant immediate investigation of medication history
- •Fetal death associated with progesterone treatment does not necessarily compromise future fertility or reproductive success, as demonstrated by this mare's subsequent normal pregnancy
Key Findings
- •Weekly long-acting progesterone injections in a pregnant mare resulted in premature lactation and fetal death at 7 months gestation
- •Fetal examination revealed growth retardation (53 cm crown-rump length consistent with 6-month fetus), edematous umbilical cord, and severely dilated urachus
- •Histopathology showed placental stromal mineralization, distended umbilical adventitia, and dilated umbilical lymphatics
- •Mare recovered well following induced abortion and successfully carried a healthy foal to term in the following breeding season