What is the likely diagnosis for a horse with an oozing circular lesion that has persisted for 3 months?

The diagnosis of melanoma for a horse with a persistent oozing circular lesion aligns with the typical characteristics of this condition. Melanomas are common in older horses, especially those with gray coats, and they often present as firm, round tumors that can ulcerate and ooze. Persistent lesions, particularly those that have been present for several months, further suggest a neoplastic process, which is consistent with melanoma.

Veterinary professionals often identify melanoma by the appearance and location of the lesions, as they commonly occur in areas like the perineum, tail, and around the ears. The prolonged duration of the lesion indicates that it is unlikely to be due to an infectious disease, which tends to have a different onset and course.

Other conditions, such as dermatophilosis, HPabronemiasis, and papillomatosis, typically have different characteristics or a different presentation timeline. Dermatophilosis, for example, is commonly seen as crusty lesions and is often associated with skin damage from moisture and is more acute. HPabronemiasis involves the horse's response to the larvae of the stomach worm and usually presents in a more acute manner with pruritic scabs, while papillomatosis is characterized by warty growths