Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares.

Abstract

BACKGROUND: 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. OBJECTIVES: 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. STUDY DESIGN: Retrospective cohort study. METHODS: Breeding records from a Warmblood stud farm were evaluated (2016-2019) and 2682&#x2009;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 &#xd7; N/WFFS (n&#x2009;=&#x2009;46), N/WFFS (mares) &#xd7; N/N (n&#x2009;=&#x2009;511), N/N &#xd7; N/WFFS (stallions) (n&#x2009;=&#x2009;191) and N/N &#xd7; N/N (n&#x2009;=&#x2009;2149). RESULTS: There were no differences in pregnancy rates between matings with only one WFFS carrier and those with non-carriers. When comparing N/WFFS &#xd7; N/WFFS matings to those with only one or no WFFS-carrier, there were no increased pregnancy losses in the embryonic phase (day <42). By contrast, the N/WFFS &#xd7; N/WFFS group had significantly more abortions (53.8%) than the other three study groups (7.9-9.2%; adjusted p&#x2009;<&#x2009;0.0001). The higher losses were evenly distributed between the early (D42-150: 22.7% losses, n&#x2009;=&#x2009;5) and late (D150-300: 29.4% losses, n&#x2009;=&#x2009;5) foetal phase. The live foal rate per pregnancy for N/WFFS &#xd7; N/WFFS matings was lowest (34.5%) and differed significantly (other groups 81%-84%; adjusted p&#x2009;<&#x2009;0.0001); the peri- and postnatal mortality was higher (25%) compared with the other study groups (2.6%-3%). MAIN LIMITATIONS: Low sample size in N/WWFS &#xd7; N/WFFS matings, unbalanced study design, outcomes are descriptive, all mares from one stud farm. CONCLUSIONS: The mating of two WFFS carriers may lead to increased risks of pregnancy and foal loss.