- Skin Cancer in Angora Goats
|Last update: March 30, 2012 11:54:40 AM|
Skin Cancer in Angora Goats
E. M. van Tonder, Regional Veterinary Laboratory, Middelburg, C.P.
SKIN cancer in Angora goats is a relatively common phenomenon in the sense that, although it does not have a high incidence in any particular flock, it does have a widespread occurrence.
In general, skin cancer is an important problem, since it shows a breed predisposition for Angora goats, is normally of a malignant nature and its course is usually fatal as the affected goat has to be destroyed eventually. This often happens long before such an animal has reached the end of its maximum productive and reproductive lifespan.
Types of Skin Cancers
Although a variety of skin cancers are encountered in Angora goats, there are mainly two types which occur on a fairly regular scale. These are:
1. Melanocytic or Pigment cancers: This group of cancers, which can either be benign or malignant, usually originates from the deeper layer of the upper skin (epidermis) where the pigment-producing cells of the skin are situated. The benign types of these cancers, which are comparable with moles in human beings, are more located and are seldom seen in goats. The malignant pigmented tumours may also penetrate the deeper layers of the skin and. may spread along the lymph tracts. Sometimes these tumours may temporarily assume a benign appearance, but eventually become malignant. The cause of this type of skin cancer is, as in other cancers, largely still unknown. Although viruses are suspected, this cause is as yet totally unproven, whereas genetic or hereditary factors are likely to play an important role in goats.
Whatever the case, these growths normally originate in areas of strongly pigmented skin, i.e. where there is a greater concentration of pigment-producing cells, as well as in certain parts where pigmentation increases with age. These tumours usually develop as a result of the uncontrolled proliferation and growth of the pigment cells. Whereas the body normally allows the multiplication and development of body cells and the replacement of tissues to occur in an orderly way, in this case, as result of the thus far unknown cause, it loses that particular ability and can therefore not exercise any control over this abnormal growth and multiplication of cells.
This aberrant development of cells results in a growth which extends into the deeper lying tissues and also erupts to the surface. Superficially a tumour of this nature may assume two different forms. In most cases it consists of a pedunculated, knob-like structure, joined to the deeper lying tissues by means of a stem. The surface has a typical lobulated, wart-like appearance. In other cases a more evenly disseminated structure is formed which slowly penetrates the superficial layers of the skin and is characterized by the formation of ulcers, which become septic as a result of secondary bacterial infection. These cancers usually have a black to brownish-black appearance. On incision this black or brownish-black pigment is freely discharged onto the hands, while it is also readily soluble in water and can easily be washed off.
In Angoras there is no difference in incidence between the sexes since it would appear that the apparent higher incidence in ewes can simply be ascribed to the difference in numbers. There are however certain predilection sites on the body of the goat where these tumours are most frequently encountered. The most important of these are the inside of the external ear, the hairless parts under the tail and around the anus, including the anus itself, and the vulva. These cancers can also spread to the lymph glands and other organs.
2. Squamous cell cancer (carcinoma): Squamous cell carcinomas are quite commonly encountered in Angora goats. Since there is also no sex predilection in this case, the apparently higher incidence amongst ewes can also be ascribed to the difference in numbers. Here again, the exact cause is unknown. In contrast to the pigment cancers, squamous cell tumours chiefly occur in the unpigmented or poorly pigmented parts of the skin. In Angora goats it again is mainly the ears that are affected, while the udder and teats are also sometimes involved.
While the unpigmented areas of the skin are predominantly affected, it would appear that exposure to bright sunlight and incessant irritation from eartags also contribute to the development of these growths. As pigmentation of the skin is involved, genetic or hereditary factors again may playa role. Squamous cell carcinomas take their origin from the two deeper cell layers of the skin and consist of irregular masses or cords of epidermal cells, which proliferate inward and invade the dermis or proper skin and subcutaneous tissues. As the cells of origin of these tumours produce and contain a horny substance (keratin), the well-developed growths, on incision show various greyish-white areas, referred to as horn or cancer pearls.
Since these cancers also extend to the surface of the skin, the external appearance may assume one of two forms, viz. a productive or proliferative and an erosive form. The productive type of tumour consists of papillary growths of varying size, many of which have a cauliflower-like appearance. The surface tends to be ulcerated and bleeds easily. The erosive types initially appear as shallow crusted ulcers, which, if allowed to develop, become deep and crater-like.
In general squamous cell tumours are locally invasive, but slow to spread to other parts of the body. Should this occur, however, the local lymph glands are invaded first, followed by the lungs. Widespread invasion of the tissues are sporadically seen.
Course, Consequences and Control of Skin Cancers
In many instances skin cancers follow a fairly protracted course, particularly in the case of squamous cell carcinomas, so that the animal will have been eliminated for some other reason or will have succumbed before the effects - and especially secondary effects- could exert their influence. There is, however, a large percentage of cases where a more rapid course is followed and animals have to be sacrificed before they reach the peak of their productive and reproductive performance. It should also be kept in mind that in all cases where incomplete surgical intervention or excessive external irritation has occurred, the course of these tumours will be accelerated considerably.
Consequences depend upon the course that skin cancers run, the size and location of the growths, and secondary infections which may set in, as well as the spreading thereof to other parts of the body. When genital organs themselves and even the surrounding areas are involved, the ability of the ewe to reproduce is affected, owing to her incapacity to receive the ram.
In the case of the ears being affected, consequences are usually the result of pain and irritation, which are naturally aggravated by secondary infections and fly and blowfly attacks. This finally leads to lack of appetite, loss of body weight and pining, with attendant production and reproduction losses. When tumours spread to other parts of the body, much depends on which organs become affected. If, for instance, the lungs, liver and kidneys were to be affected, the course of the affliction would be fairly quick and would be accompanied by rapid emaciation and eventual death.
Treatment depends on the location of the tumour, since the, only true method consists in complete surgical removal. In such cases the whole tumour, as well as surrounding potentially cancerous tissue, must be removed. Usually this is not possible when growths are situated near the anus and vulva. Where the ears are affected and the lesions are not too big, portions of the ear may be amputated, and, in the case of pigment cancers, the surrounding over-pigmented areas of the ear should also be removed. Owing to the fact that heredity may playa role as far as both kinds of cancers are concerned, especially regarding over- or unpigmented areas of skin, stricter selection in this respect can be considered. This will be of particular value where indications of a possible genetic factor appear to exist.