[Comparative investigations of depigmented and melanomatous lesions in gray horses of the lipizzaner breed (author’s transl)].

This research looked into the pigmentation and skin structure of Lipizzaner horses. It particularly compared depigmented (loss of skin color) and melanomatous (skin with tumors) characteristics in older and younger horses of this breed, also studying cellular-level properties. The findings demonstrated an increase in melanomas in older horses, as well as a correlation between graying of hair and skin depigmentation.

Exploration of Pigmented, Depigmented, and Melanomatous Skin

• The study made use of clinical, light-, and electron microscopic methods to inspect the morphological changes on the skin of the Lipizzaner breed from the Vienna Spanish Riding School.
• The research aimed to study the structural characteristics of melanomas (skin tumors), and the differences between pigmented (color-bearing) and depigmented (colorless) skin.

Influence of Age and Melanoma Appearance

• In a group of 31 older horses (aged 10 years or above), 20 were found to have melanomas. On the other hand, in a set of 23 younger horses (under the age of 10 years), no visible evidence of melanotic tumors was found.
• The research suggests that age might be a factor in the development of these tumors, with older Lipizzaner horses showing a higher rate of melanomas.

Study of Depigmentation and Melanocyte Behavior

• Observable depigmentation of the skin frequently coincided with the graying of the hair in the studied horses. This demonstrates a clear correlation between graying and depigmentation.
• The skin biopsies of the studied animals were inspected using light and electron microscopic techniques. In pigmented skin, melanin was found to be produced by DOPA-positive melanocytes and stored as large, single melanosomes within keratinocytes.
• In contrast, depigmented skin lacked melanocytes and melanosomes entirely. However, it did contain a high number of indeterminate cells in the basal layer.

Observations on Tumor Formation and Cell Differentiation

• Melanotic tumors (commonly appearing at the root of the tail, lips, perianal region, shoulder, and intestinal lymph nodes) exhibited characteristics similar to blue nevi in the dermis – encapsulated nodules or diffusely infiltrating structures.
• The study was unable to observe any junctional activity, a characteristic that points to malignant melanoma.
• Differentiating between melanin-producing tumor cells and melanophages (cells that consume and degrade melanin) was found to be challenging through light microscopy, but became possible when using ultrastructural characteristics for differentiation.