Limbal squamous cell carcinoma in Haflinger horses.

Objective: To describe the prevalence of LSCC in Haflinger horses and to analyze affected horses' pedigrees investigating the genetic mode of inheritance.

Animals: Fifteen horses met inclusion criterion of (i) being of the Haflinger breed, as confirmed by North American Haflinger Registry pedigree and (ii) being diagnosed with LSCC, as confirmed by clinical examination by a veterinary ophthalmologist or by histopathology. Pedigrees could not be obtained for four additional horses diagnosed with LSCC that had been identified as Haflingers.

Procedure: Retrospective medical record review of all 19 horses was used to determine patient sex and age at diagnosis. The four-generation pedigrees available for 15 of the horses were used to perform pedigree analysis.

Results: Average age of 19 Haflingers at diagnosis with LSCC was 8.7 years. Eleven were males and eight were females. Thirteen of 15 affected horses for whom pedigrees were available shared a common ancestor within five generations, and all 15 shared a common ancestor from the A stallion line in the breed pedigree. Pedigree analysis identified a common sire of two of the affected male horses. Clinical examination of this sire that had no history of LSCC showed no current clinical signs of LSCC, suggesting an autosomal recessive mode of inheritance.

Conclusions: Haflingers may be over-represented amongst horses with LSCC and may be diagnosed at a younger age than other breeds. Affected Haflingers appear closely related, suggesting a possible heritable basis for LSCC. The genetic basis for LSCC will be investigated further by a GWAS approach.