The aim of this master’s thesis was to evaluate the importance of genetic testing and to determine the presence and potential risk of inherited diseases in Quarter Horses in Slovenia. The study included 74 horses, of which 73 were Quarter Horses and one was a Paint Horse, representing approximately 12% of the Slovenian Quarter Horse population at the time of the study. Four genetic diseases with significant implications for equine health and breeding were investigated: hereditary equine regional dermal asthenia (HERDA), hyperkalemic periodic paralysis (HYPP), polysaccharide storage myopathy type 1 (PSSM1), and malignant hyperthermia (MH). Genomic DNA was isolated from blood samples and analyzed using polymerase chain reaction (PCR), PCR–restriction fragment length polymorphisms (PCR-RFLP), and DNA sequencing. The success of PCR amplification and restriction was verified by gel electrophoresis, and the presence of mutations was confirmed by sequencing selected samples. The results revealed that 14.9% of the analyzed horses were heterozygous carriers of the mutation associated with HERDA, while no homozygous individuals for the mutant allele were detected. No mutant alleles were identified for HYPP or MH in the analyzed samples. One heterozygous carrier of the PSSM1 mutation was detected; however, this individual did not belong to the Quarter Horse breed, and therefore the prevalence of PSSM1 within the Quarter Horse population could not be assessed. The findings confirm the presence of disease-causing alleles in the Slovenian Quarter Horse population and emphasize the importance of systematic genetic testing and responsible breeding strategies for improving the long-term genetic health of the breed.
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