Neoplasia

The most common skin tumors of the goat are cutaneous papilloma (warts), squamous cell carcinoma, and mela­noma. Hemangioma, hemangiosarcoma, histiocytoma, mast cell tumor, sebaceous gland tumors, and cutaneous lymphosarcoma have also been reported (Bastianello 1983; Manning et al.

Papilloma

Common warts probably occur much more frequently in goats than the caprine literature suggests. This is because those on the head or neck are benign and often self-limiting. If noticed at all, they are recognized as warts and, because of a favorable prognosis, biopsy or treatment is not attempted. Favorable response to autogenous vac­cine, after surgical removal of the largest warts, has been reported in a study with no untreated controls (Rajguru et al. 1988). The involvement of multiple animals in one closely confined herd has been taken as evidence for an infectious origin (Davis and Kemper 1936), although a wart virus has rarely been demonstrated in caprine papillomas (Simeone et al. 2008).

Udder Warts

Warts on the udder have a different clinical course and are apparently limited to white goats (Saanens or Angoras) that have lactated at least once (Moulton 1954; Ficken et al. 1983; Theilen et al. 1985). The papillomas involve the white skin of both udder and teats and are typically multi­ple (Figure 14.7). They may either be flaky or form elon­gated cutaneous horns. Some transform into squamous cell carcinomas with a wide base and ulcerated surface. The carcinomas may rarely metastasize to the supramammary lymph node. A papillomavirus is possibly involved in the pathogenesis (Manni et al. 1998). Additional discussion of these tumors is included in Chapter 14.

Carcinomas

Carcinomas of the skin also occur on other regions of the goat and without a preceding papilloma lesion. Again, white breeds in sunny climates are at risk. Angoras and Boer goats frequently develop carcinomas of the perineum (vulva and anus; Thomas 1929; Curasson 1933; Hofmeyr et al. 1965; Yeruham et al. 1993; Lohr 2012). Ears, horn stumps, and muzzle (van der Heide 1963) may also be involved. The tumor may be sessile or pedunculated and becomes ulcer­ated as it enlarges. Detection often follows development of a foul-smelling exudate (Ramadan 1975). Possible origins for these tumors include squamous cells, basal cells, and seba­ceous glands. Early surgical treatment is curative; otherwise affected animals should be culled. An affected ear can be easily amputated using local anesthesia and a Burdizzo emasculatome, placed on an angle to give a more cosmeti­cally acceptable pointed shape to the remaining ear carti­lage. Myiasis hastens the death of animals left untreated.

Melanomas

Melanomas appear to involve the same skin areas as the carcinomas, especially the vulva, perineum, and ear (Venkatesan et al. 1979; Bastianello 1983; Ramadan and El Hassan 1988). Indeed, it is sometimes unclear whether a given tumor is a pigmented basal cell carcinoma or a mela­noma (Jackson 1936). In other instances, both clinical course (metastases to internal organs) and histologic find­ings are consistent with malignant melanoma (Sockett et al. 1984). One case in a Pygora goat appeared to originate at the base of the horn, but infiltrated local tissues and metastasized to the regional lymph node, salivary gland, and liver (Mavangira et al. 2008). A direct smear of the tumor may be diagnostic.

The prognosis for melanomas is poor, as metastases com­monly occur to local nodes, liver, and lung. A breed predi­lection was demonstrated in the Sudan in a review of 62 affected goats; the gray or brown “American” goats origi­nally imported from Syria were more commonly affected than the more numerous all-black native Nubian goats (Ramadan and El Hassan 1988). The Angora goat has been proposed as a model for human melanomas, because both tumors and benign melanocytic lesions can be induced by exposure to sunlight (Green et al. 1996).