Characterization of abortion, stillbirth and non-viable foals homozygous for the Warmblood Fragile Foal Syndrome

Warmblood fragile foal syndrome (WFFS) is a monogenetic defect with autosomal recessive inheritance. The WFFS homozygosity is non-compatible with extra-uterine life. Although as many as 15% of Warmblood horses are WFFS carriers, there has been little veterinary focus on this condition. The aim of this study was to determine outcomes and symptoms of clinical signs and pathological abnormalities during pregnancies when there were WFFS homozygous foetuses. Diagnostic material of 15 abortion or stillbirth cases with suspected diagnosis of WFFS was available for this study. Additionally, there were examinations in 37 cases where there were no indications of WFFS when submitted for routine diagnostic procedures. Foals in all cases were genotyped and external morphological defects were recorded. Amongst the 15 cases in which WFSS was suspected, there were 14 homozygous foetuses with the WFFS allele (WFFS/WFFS). Three heterozygous WFFS foetuses (N/WFFS) were detected in the cases submitted for routine diagnostic procedures. Of the 14 WFFS homozygous foetuses, 11 of mares had a gestation length of at least 320 days. Nine foals were born alive but died within a short time. Skin defects were obvious in 12 WFFS homozygous foals, and there was abnormal flexibility in the digital joints, flexed forelegs and incomplete closure of the abdominal wall in five, four, and one of the foals, respectively. In conclusion, the predominant manifestation of WFFS are death during the latter stages of gestation or live births with foals being non-viable. Losses in Warmblood horse breeding caused by WFFS are greater than previously assumed.