Performance of Swedish Warmblood fragile foal syndrome carriers and breeding prospects

Michela Ablondi,Sofia Mikko,Åsa Gelinder Viklund,Alberto Sabbioni,Martin Johnsson,Susanne Eriksson

doi:10.1186/s12711-021-00693-4

Abstract

BackgroundWarmblood fragile foal syndrome (WFFS) is a monogenetic defect caused by a recessive lethal missense point mutation in the procollagen‐lysine, 2‐oxoglutarate 5‐dioxygenase 1 gene (PLOD1, c.2032G>A). The majority of homozygous WFFS horses are aborted during gestation. Clinical signs of affected horses include fragile skin, skin and mucosa lacerations, hyperextension of the articulations, and hematomas. In spite of its harmful effect, a relatively high frequency of WFFS carriers has been found in Warmblood horses, suggesting a heterozygote advantage. Thus, in this study our aims were to: (1) estimate the frequency of WFFS carriers in the Swedish Warmblood breed (SWB), (2) estimate the effect of WFFS carrier genotype on performance traits in two SWB subpopulations bred for different disciplines, and (3) simulate the potential effects of balancing selection and different selection strategies on the frequency of carriers.MethodsIn total, 2288 SWB sport horses born between 1971 and 2020 were tested for the WFFS mutation and had estimated breeding values (EBV) for ten traditional evaluating and 50 linear descriptive traits.ResultsThe frequency of WFFS carriers calculated from a pool of 511 randomly selected SWB horses born in 2017 was equal to 7.4% and ranged from 0.0 to 12.0% among the whole set of tested SWB horses, starting from 1971 till 2020. The effect of the WFFS carrier genotype was significant for several EBV mainly related to movements and dressage traits and especially for horses not bred for the show jumping discipline. Using simulation, we showed that balancing selection can maintain a recessive lethal allele in populations such as the SWB breed over generations and that the frequency is expected to slowly decrease in absence of balancing selection. Finally, we showed that selection against carrier sires can result in a more rapid decrease of the frequency of the mutant allele over time.ConclusionFurther research is needed to confirm the apparent association between equine performance and the WFFS carrier genotype. Identification of such associations or new causative mutations for horse performance traits can serve as new tools in horse breeding to select for healthy, sustainable, and better performing horses.

Highlights

Warmblood fragile foal syndrome (WFFS) is a monogenetic defect caused by a recessive lethal mis‐ sense point mutation in the procollagen‐lysine, 2‐oxoglutarate 5‐dioxygenase 1 gene (PLOD1, c.2032G>A)
In this study, we estimated the frequency of carriers of the WFFS allele in the Swedish Warmblood breed (SWB) breed and found that the WFFS allele is associated with advantageous effects on several performance traits, especially those related to movements, which was more marked in the non-show jumping (NS) SWB horses
Our findings suggest the potential presence of balancing selection for the WFFS allele in SWB horses that are bred for dressage purposes

Summary

Introduction

Warmblood fragile foal syndrome (WFFS) is a monogenetic defect caused by a recessive lethal mis‐ sense point mutation in the procollagen‐lysine, 2‐oxoglutarate 5‐dioxygenase 1 gene (PLOD1, c.2032G>A). In spite of its harmful effect, a relatively high frequency of WFFS carriers has been found in Warmblood horses, suggesting a heterozygote advantage. Warmblood fragile foal syndrome (WFFS) is an autosomal monogenetic disease that has raised much concern among warmblood horse breeders in recent years due Ablondi et al Genetics Selection Evolution (2022) 54:4 homozygous foals are assumed to be lost by abortion during late gestation. In spite of the harmful effect of the mutation in the homozygous state, the frequency of WFFS carriers is relatively high in Warmblood breeds. The lethal WFFS allele has not been detected in most non-warmblood breeds, which supports the exclusivity of the WFFS mutation to Warmbloods and Thoroughbred horses [6, 9]. A recent study found a few WFFS carriers in Paint, Quarter, and Haflinger horses [10]

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