Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares.
Authors: Kehlbeck A, Blanco M, Venner Monica, Freise Fritjof, Gunreben B, Sieme Harald
Journal: Equine veterinary journal
Summary
# Warmblood Fragile Foal Syndrome: Understanding Pregnancy Loss Risk Warmblood fragile foal syndrome Type 1 (WFFS) is a recessive genetic condition long associated with late abortions, stillbirths and non-viable foals, yet whether early pregnancy losses occur has remained unclear. Kehlbeck and colleagues analysed 2,682 breeding cycles across 177 mares at a single stud farm (2016–2019), stratifying matings by WFFS carrier status to establish whether pregnancy outcome differed between dual-carrier pairings, single-carrier pairings and non-carrier controls. Conception rates proved comparable across all groups; however, dual-carrier matings (N/WFFS × N/WFFS) demonstrated dramatically elevated pregnancy losses at 53.8% abortion rate versus 7.9–9.2% in other groups, with losses distributed evenly across the early foetal phase (day 42–150) and late foetal phase (day 150–300), and live foal rate dropping to just 34.5% compared with 81–84% elsewhere—additionally, peri- and postnatal mortality reached 25% in dual-carrier offspring. The absence of increased embryonic losses (pre-day 42) before the foetal phase suggests the WFFS phenotype manifests later in gestation, with critical implications for breeding programmes: single-carrier matings carry no measurable reproductive penalty, whilst dual-carrier pairings present unacceptable risk and should be avoided through genetic testing and informed breeding decisions.
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Practical Takeaways
- •Breeding two WFFS carriers significantly increases risk of pregnancy failure and foal loss; genetic testing and carrier screening should guide breeding decisions to avoid N/WFFS × N/WFFS matings
- •Mating one WFFS carrier with a non-carrier (N/N) shows pregnancy success rates equivalent to N/N × N/N matings, suggesting single-carrier status poses minimal breeding risk
- •Pregnancy monitoring and management should be intensified in known N/WFFS × N/WFFS matings, as losses occur throughout gestation rather than early embryonic loss alone
Key Findings
- •N/WFFS × N/WFFS matings resulted in 53.8% abortion rate compared to 7.9-9.2% in other groups (p<0.0001)
- •No increased embryonic losses (<day 42) in N/WFFS × N/WFFS matings, but significant losses evenly distributed across early fetal (day 42-150: 22.7%) and late fetal phases (day 150-300: 29.4%)
- •Live foal rate per pregnancy was lowest in N/WFFS × N/WFFS group at 34.5% versus 81-84% in other groups (p<0.0001)
- •Perinatal and postnatal mortality was 25% in N/WFFS × N/WFFS matings compared to 2.6-3% in other study groups