Effects of maternally administered depot ACTH(1-24) on fetal maturation and the timing of parturition in the mare.
Authors: Ousey J C, Rossdalet P D, Palmer L, Grainger L, Houghton E
Journal: Equine veterinary journal
Summary
# Editorial Summary: Maternal ACTH Administration and Fetal Maturation in Mares Premature delivery in mares can result in immature foals with serious health complications, making strategies to accelerate fetal development clinically valuable. Ousey and colleagues administered synthetic depot ACTH(1-24) to 22 mares at 300–302 days gestation (low dose: 1 mg; higher dose: 4–5 mg), stratifying results by breeding season timing and comparing outcomes against 64 untreated control mares. High-dose ACTH given to mares bred after 1 July significantly shortened gestation by approximately 9 days (318 versus 327 days in untreated late-bred mares, P<0.01), stimulated mammary development and appropriate milk electrolyte changes, and resulted in mature foals—though two were stillborn with indicators of prematurity (elevated MCV, lower bodyweight). The maturation-accelerating effect appeared dependent on both dosage and breeding season, with high doses producing prolonged cortisol elevation and higher plasma progestagens compared to low-dose protocols. Whilst these findings suggest maternal ACTH administration could manage pregnancies at risk of dysmaturity, the authors emphasise that further research into optimal gestational timing and dosing is essential before clinical protocols can be confidently recommended for equine practice.
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Practical Takeaways
- •High-dose maternal ACTH can induce premature fetal maturation and earlier delivery in mares, but carries risk of stillbirth and immature foals; clinical use is not yet recommended without further dose optimization studies
- •Timing of breeding season significantly influences ACTH response, with late-season mated mares showing greater sensitivity to ACTH-induced acceleration of parturition than early-season mares
- •If considering ACTH administration for fetal maturation, monitor foal maturity indicators (MCV, bodyweight) carefully and recognize that optimal gestational age and dosage protocols remain undefined
Key Findings
- •Maternal depot ACTH administration at high dose (4-5 mg) significantly shortened gestation length in mares mated late in breeding season (318±1.8 days vs 327±1.3 days in untreated controls, P<0.01)
- •High-dose ACTH significantly elevated plasma progestagen and cortisol concentrations and stimulated mammary development and milk electrolyte changes
- •High-dose ACTH given to late-season mares produced foals with higher MCV and lower mean bodyweight, indicating premature delivery before full term with 2 stillbirths among 10 foals
- •Low-dose ACTH (1 mg) did not significantly shorten gestation compared to untreated mares (335±3.7 days), suggesting dose and breeding season timing are critical variables