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The report describes two cases of four- and five-month-old Mangalarga Marchador fillies showing signs of night blindness. The animals appeared to have disorientation at night. Ophthalmic examination revealed all parameters as normal except for the absence of menace response in the penumbra. Fundoscopy examination did not demonstrate any morphological abnormalities in the retina. Electroretinography examination confirmed a failure in the electrical activity of rods, which are retinal photoreceptors responsible for night vision. However, we noted a small reduction in the electrical activity of the cones, suggesting that the animals may have visual difficulties in clear environments. Genomic analysis of the hair follicles from their mane (Veterinary Genetics Laboratory/UC – Davis, USA) did not reveal the presence of homozygosity for the Leopard Complex, a gene pool associated with congenital stationary nocturnal blindness (CSNB) in horses with depigmented hair. Outcomes of the studbook analysis suggested the presence of kinship among the described animals. Additional research is required for the genomic determination of nocturnal blindness in Mangalarga Marchador horses.