Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype.

The research paper investigates the correlation between deafness in American Paint Horses and several factors: their physical characteristics (phenotype), their brainstem auditory-evoked responses (BAERs), and their endothelin receptor B (EDNBR) genotype. The findings reveal a strong link between deafness and certain traits, such as the splashed white or frame overo coat color pattern, extensive white head and limb markings, and blue eyes.

Methodology of the Study

• The study was segmented into case series and case-control studies, involving 14 deaf American Paint Horses, 20 suspected-deaf American Paint Horses, and 13 nondeaf American Paint Horses and Pintos.
• Horses were categorized according to their coat color patterns and eye color. They were tested for the EDNBR gene mutation (commonly associated with overo lethal white foal syndrome). The horses also underwent Brainstem Auditory-Evoked Responses (BAERs) tests.
• Further clinical findings were gathered from the horses’ medical records.

Key Findings of the Study

• All 14 deaf horses exhibited a loss of all waveforms on their BAERs test, which is consistent with complete deafness.
• The majority of these horses exhibited a splashed white or splashed white-frame blend coat pattern. Other observed patterns include frame overo and tovero.
• The deaf horses all showed extensive white head and limb markings while having at least one partially heterochromic iris – most had two blue eyes.
• Ninety-one percent (31 out of 34) of the deaf and suspected-deaf horses were found to have a mutation in the EDNBR gene.
• Horses with no hearing loss displayed normal BAER test results.

Implications of the Study

• The study suggests that veterinarians should be aware of the potential for deafness in American Paint Horses, particularly those with a splashed white or frame overo coat color pattern, or a blend of these patterns.
• Horses with extensive white markings on the head and limbs and those with blue eyes appear to be at a particular risk for deafness.
• Despite their hearing loss, the deaf and suspected-deaf horses were able to perform various events successfully, indicating that deafness did not affect their performance capabilities.