The third eyelid is a common area for cancer in cattle, which can be removed surgically if found early enough
Cancer eye, formally known as bovine ocular squamous cell carcinoma, is the most common type of cancer in cattle.
About 80 percent of tumours reported at slaughter are related to the eye and they are a leading cause of carcass condemnation at packing plants. Cancer eye causes significant economic loss to cattle producers due to the decreased salvage value of affected cattle, carcasses condemned in advanced cases, and shortened productive life of the animal.
Cows with cancer eye are often culled during their productive years but if the condition is detected early, it can almost always be successfully treated and cured.
Dr. Rob Swackhammer, a large animal veterinarian at Upper Grand Veterinary Services in Guelph, Ont., worked for 12 years at the veterinary school in Guelph as a clinical instructor and for the past 10 years has worked in private practice.
“I’ve seen a fair number of cancer eyes,” he said. “We used to think this was just a Hereford problem, but now realize that breed doesn’t matter as much as having no pigment around the eye.”
Other animals with light-coloured skin or hair are also susceptible. Dark colours provide more protection against ultraviolet rays, which can irritate the tissues and are more readily reflected into the eye if skin and hair are light.
Breeders often try to select animals with pigment around the eyes. Other species, including horses, experience problems in animals with little pigment around the eyes.
“In cattle, we see an occasional animal with tissue protruding from the eye, and tears running down the face, often the first signs there’s irritation of the eye that might be cancer,” said Swackhammer.
“The third eyelid (in the inside corner of the eye) is a common area for cancer. If it’s protruding or irritated, it needs a closer look. Cancer in third eyelid can be removed surgically, if we find it early,” said Swackhammer.
“We can administer local anesthetic and use forceps to stabilize that tissue and with a scalpel blade or scissors remove affected tissue. This is quick and easy and requires very little follow-up.”
Cancer of the third eyelid should be removed as soon as it’s noticed because tumours can spread into the eye socket and surrounding bones, metastasizing more quickly than tumours on the eyeball.
Cancer on the eyeball occurs where white and dark portions meet. A growth at the edge of the eye begins as a small white or sometimes pink plaque that is easily seen at close range. This type of lesion usually grows slowly and may take months or years to develop into a malignant tumour. It’s trickier to remove because it is on the eyeball itself.
“If we find this on a cow’s eye when preg-checking, I generally ask the owner to re-book and I’ll come back another day to remove it because it takes longer,” said Swackhammer.
“I use a nerve block so the eye won’t be moving, and we can open the eyelids fully and stabilize the eye. We don’t want the cow or the eye to move when we’re slicing off that little growth with a scalpel blade.”
In some situations a veterinarian will cauterize or freeze the area after removing the plaque to kill stray cancer cells left in surrounding tissue.
“Worst case scenario, if the cancer wasn’t seen early and might be more deeply involved, we remove the eye,” he said.
“There are meat quality issues if cancer spreads beyond the eye itself. This is why the entire carcass will be condemned if there’s any chance it has spread. Some producers ask us to remove the eye rather than send the cow to slaughter and not having it pass.
“The owner may elect to have the eye removed so the cow can finish her pregnancy and raise one more calf or finish raising the calf at her side.”
Warty tumours on the outer eyelid are not usually cancerous but can be precursors. They can be burned off with an electrical probe or by freezing.