Research probes mysteries of grey horse melanomas

A University of Queensland study of melanoma tumours in grey horses may also lead to a better understanding of pigment cell disorders and malignancies in humans.

Veterinarian Glen Coleman said his PhD research was useful at a time when the incidence of malignant melanoma remained high and affected large numbers of relatively young people.

The behaviour of cells was similar in horses and humans, and the genes which governed coat colour and pigmentation in animals were likely to have equivalents in people, for example those with red hair or freckles.

A greater understanding of grey horse melanoma will also help veterinarians in the treatment and management of the condition.

Mr Coleman said most grey horses had heavily pigmented internal lesions. However, his research suggested the tumours were not malignant.

Microscopic study revealed benign features and they appeared to occur along set paths rather than spreading, like most malignant tumours, to major organs such as the liver and lungs.

Another pointer suggesting these tumours were not malignant was that they rarely seemed to affect the horse's health or lead to the animal's death.

Mr Coleman said grey horses could be born any colour but their coats lightened to grey and eventually white as the animals grew older.

'Heavily pigmented tumours develop in many of these animals, apparently concurrent with the dilution in coat colour,' he said.

His research suggested tumours formed as the hair follicles lost their ability to produce pigment or to pass it on to the growing hair. Pigment then accumulated in slowly enlarging masses, the grey horse melanomas.

Mr Coleman reached his conclusions after studying 70 grey horses. Sixty of these showed evidence of tumours, including all the 22 horses estimated to be aged 15 or over. A further 16 coloured horses showed no signs of the disease.

'I think it's safe to conclude that all greys will develop melanoma tumours if they live long enough,' Mr Coleman said. 'Tumour development can be thought of as an inevitable consequence of coat colour dilution.'

For further details, contact Mr Glen Coleman (telephone 3365 2119).