Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares

Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares
Equine Vet J. 2024 Nov 14. doi: 10.1111/evj.14435. Online ahead of print.
Authors
A Kehlbeck 1 2 , M Blanco 2 , Monica Venner 3 , Fritjof Freise 4 , B Gunreben 5 , Harald Sieme 6
Affiliations

1 Lewitz Stud, Neustadt-Glewe, Germany.
2 Clinic for Horses, University of Veterinary Medicine Hanover, Hanover, Germany.
3 Equine Clinic Destedt, Cremlingen, Germany.
4 Department for Biometry, Epidemiology and Information Processing, University of Veterinary Medicine Hanover, Hanover, Germany.
5 Laboklin, Bad Kissingen, Germany.
6 Clinic for Horses – Unit for Reproductive Medicine, University of Veterinary Medicine Hanover, Hanover, Germany.

PMID: 39539185
DOI: 10.1111/evj.14435

Abstract
in English, German

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 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).

Results: 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 <42). By contrast, the N/WFFS × N/WFFS group had significantly more abortions (53.8%) than the other three study groups (7.9-9.2%; adjusted p < 0.0001). The higher losses were evenly distributed between the early (D42-150: 22.7% losses, n = 5) and late (D150-300: 29.4% losses, n = 5) foetal phase. The live foal rate per pregnancy for N/WFFS × N/WFFS matings was lowest (34.5%) and differed significantly (other groups 81%-84%; adjusted p < 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 × 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. Keywords: WFFS; equine pregnancy loss; equine reproduction; horse. © 2024 EVJ Ltd.