Note Number: AG1112
Katie Rutter (Swan Hill) and Louise Wood (Kyneton)
Updated: October 2003
WARNING: Some photos contained in this Agriculture Note could offend some readers. However, this graphical representation is necessary to allow for the correct identification of cancers in livestock.
There are many different types of cancer (malignant tumour) that can affect livestock, however most are rare. In Australia, the most common cattle and sheep cancers affect the skin and eyes, and are caused by the sun's ultraviolet radiation irritating exposed areas of the skin.
Cancers can become an animal welfare issue if left untreated, and can affect the public's perception of the quality of meat that enters the human food chain. It is an unacceptable practice to "keep the cow until the calf is weaned" or to "keep the sheep until the fleece is shorn", if the animal is suffering from a malignant tumour. If malignant tumours are found in animals slaughtered at abattoirs, all or part of the carcass may be rejected.
Hereford cattle and to a lesser extent Friesian cattle and their crosses are more predisposed than other breeds to developing eye and skin cancers.
Sheep that have been badly mulesed, or had their tails docked too short are predisposed to cancers. Sun damage to bare areas of unpigmented skin plays a large role.
In cattle, prominent eyeballs and third eye lids and lack of pigmentation of the skin around the eyeball and eyelids are known risk factors.
Skin cancers begin as red, sun-damaged patches. The irritated patch of skin thickens and spreads, eventually invading surrounding tissues. As the tumour grows it may cause severe irritation and distress to the animal, depending on location, particularly if it ulcerates and bleeds, and becomes infected or fly blown. Cancers will eventually grow to a size that causes interference with grazing and normal behaviour, and eventually lead to loss of condition and death.
Eye cancers will eventually spread to the lymph nodes of the head and to other body organs if left untreated. Eye or facial cancers may spread to the respiratory system, making breathing difficult.
Selecting Hereford and Friesian breeding stock with dark pigmentation of the eye and eyelids can decrease the incidence of eye cancer.
In sheep, leaving skin on top of the tail during the mulesing operation and permitting tail length to extend to the tip of the vulva, or equivalent in wethers, will offer some protection.
Regularly inspecting stock will assist the early detection of tumours, allowing treatment by a veterinarian or sale for slaughter in their earliest stages. In most cases, a veterinarian can successfully treat early stages of cancer by surgically removing the affected area and/or treating it with cryosurgery (freezing) or radiation. This usually allows unrestricted sale of the animal for full value.
It is illegal to bring livestock with cancer into Victoria without a licence, and is illegal to put cattle or sheep affected with malignant tumours in a Victorian saleyard. Exceptions are made for early stage skin and eye cancers that are less than the size of a 5 cent coin and are not bleeding or discharging. However these animals may be sold for slaughter only.
If the eye cancer is between the size of a 5 and 20 cent coin and not bleeding or discharging the animal may go direct to an abattoir to be slaughtered at owner's risk of non-payment. Tumours should never be allowed to get to a stage where they are larger than this. For more information See related Agriculture note: Eye cancers in cattle.
Figure 1. Udder cancer on a Friesian cow
Figure 2. A tumour on a sheep's ear
Figure 3. A tumour on the nose of a cow. Note: the tumour has spread to the neck.
Figure 4. A tumour on a ewe's vulva
Figure 5. Eye cancer in a hereford cow
Under the Prevention of Cruelty to Animals Act, people may be prosecuted if they allow cancers to remain untreated on animals under their care. In all cases, treatment in the earliest stages or humane slaughter at an early stage is necessary. Cancer affected animals that are not acceptable for slaughter at an abattoir must be killed humanely on farm. The carcass can be burnt, buried or removed by a knackery service.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.