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Equine deafness is difficult to diagnose.

There is a link between skin pigment and deafness in some animals; some white cats are born deaf, while Dalmations and border collies have an increased likelihood of this impediment if they have blue eyes.

The reason for this link is that the inner ear relies upon a small number of pigment-producing cells — melanocytes — to function correctly.

Melanocytes are made from the same cells that give pigment to skin and hair, so where there are abnormalities of coat colour, there may be hearing issues.

With this in mind, US research vets studied American paint horses — these animals are prone to having white patches or spots and blue or pink eyes.

The hearing ability of horses with white, or mainly white, faces and with one or two blue eyes was measured.

Clinical hearing tests and nerve activity detectors were used to test their hearing and their genetics were analysed.

Vets confirmed that there is a significant link between the amount of white splashing and hearing ability.

The presence of at least one blue eye combined with a full white face is an indicator that deafness should be considered, especially in the pattern of markings known as overo or tovero.

The results also show that deafness is genetically linked.

This research doesn’t suggest that all American paint horses with these patterns are deaf, but it highlights an important linkage of which owners should be aware.

For all the latest veterinary research and developments, see the current issue of Horse & Hound (31 December, ’09)

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