Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares

Fragile foal syndrome (FFS) or warmblood FFS Type 1 (WFFS) is a recessive, autosomal, hereditary, genetic defect causing late abortions, stillbirths and non-viable foals. Whether early pregnancy losses occur is unknown. To investigate how WFFS affects pregnancies and whether early pregnancy losses occur in WFFS matings and if there is a difference in pregnancy success between matings where both parents were allele carriers and those where only mare or stallion were WFFS carriers. Retrospective cohort study. Breeding records from a Warmblood stud farm were evaluated (2016-2019) and 2682 cycles of 177 mares analysed. Matings were assigned to four study groups, depending on the WFFS carrier status of the mare and stallion: N/WFFS × N/WFFS (n = 46), N/WFFS (mares) × N/N (n = 511), N/N × N/WFFS (stallions) (n = 191) and N/N × N/N (n = 2149). There were no differences in pregnancy rates between matings with only one WFFS carrier and those with non-carriers. When comparing N/WFFS × N/WFFS matings to those with only one or no WFFS-carrier, there were no increased pregnancy losses in the embryonic phase (day