Dr Shane Thomson, Holbrook Vet Centre. Image supplied
Finding ways to reduce the exposure of cattle to ultraviolet light with shade or shelter in paddocks and feedlots is key to helping reduce the incidence of the debilitating eye disease, pink eye.
Specialist cattle veterinarian Dr Shane Thomson, Holbrook Vet Centre, was a guest speaker at the Pasture Agronomy Service conference in Wagga Wagga on July 1, and outlined the prevention and management of pink eye in cattle.
Dr Thomson said there was a need for further research into the risk factors and causal relationships of pink eye. He pointed to recent studies revealing local immunity may be achieved by using intra-nasal or eye spray vaccine, but they were not a cure for the disease.
With the Department of Agriculture estimating lost annual production valued at over $23 million to the disease, young bos Taurus cattle in close congregation or in intensive grazing areas in southern Australia are at significant risk of contracting pink eye.
“The big question is where do we go in the future as it is not a simple infectious disease but a complex syndrome, and we don’t know enough about it,” Dr Thomson said.
“Pink eye is a common, economically important potentially contagious eye disease in cattle that is predisposed by an initial injury and can lead to substantial production loses.
“Based on the sale of commercial products in all Australian states, 10 per cent of the Australian cattle herd are treated annually but there are many cattle going untreated or treated with non-commercially available products.
“Globally the prevalence is 3 per cent so Australia is a bit of a hot spot.”
Dr Thomson said pink eye can affect up to 80 per cent of animals in a single mob.
“The impact on animal welfare is coming from the ulceration of the cornea, which often progress to painful deep melting ulcers, eyeball rupture, blindness and weight loss,” he said.
“This leads to a suppression of reproductive targets in the system and a negative impact on producer welfare – nobody working in agriculture wants to see animals suffering.
“Pink eye has been reported in literature for 130 years and there has been ample opportunity to put research into it, yet we still seem to have very little control.
“We see pink eye worse now and coming at a cost of the environmental factors driving profitability through improved efficiency and stocking rates.”
Dr Thomson said treatment and prevention had evolved over the last 10 years.
“People feel stressed about continually seeing eyes with some degree of lesions and feeling the responsibility to do treatment when a lot of the time they don’t need treating,” he said.
“The earlier we can identify and treat pink eye, the better the outcome will be. We can’t do a lot for those big yellow, melting ulcers as it is the body in the end stage of a chronic inflammatory process. These need anti-inflammatories and protection from UV light by patching.
“Try isolation to reduce spread if you see a small ulcer, blueness to the eye, tearing and squinting. Stage two is a full-blown inflammatory reaction around the eye and a melting ulcer, while stage three is pus filled eyeballs and stage four is a rupture with protrusion of inflammatory cells.
“If you can see small blood vessels venturing across the eye, that is the body healing the eye following the normal inflammatory process and treatment at that point is unnecessary.”
Dr Thomson said ensuring adequate immune competence would help prevent bacterial incursion of the eye and enhance healing, following any trauma.
He said recently traumatised corneas can heal within 36 hours provided the eye is protected from UV light.
“The biggest part of immune competence is nutrition, with any deficiencies addressed in copper, selenium, and vitamin A. If animals are healthy, they have a much better ability to fight this disease.
“Other stresses such as parasites, environmental conditions, or low feed quality (grass seeds and dust out of hay, paddocks with rank pasture and stems) will reduce their ability to fight pink eye.
“Any feeders elevating fodder for animals are typically associated with a lot more eye disease and injury as opposed to animals feeding in a bunk or on the ground. Be careful of anything that will promote foreign material going into the eyes of cattle on feed.”
UV radiation alone can induce pink eye lesions in the absence of other factors and proves the importance of having shade for feedlot cattle.
“UV light is a huge component and has been underrated in its influence on pink eye expression and is related to the shape of the eye or hooding. British bred cattle have corneas well exposed to UV radiation,” Dr Thomson said.
“Dust and flies are critical – flies are capable of creating primary trauma themselves as well as being a vector to inoculating eyes with bacteria.
“You do need some trauma to the surface of the cornea to get an infection. Once the damage occurs, it is spread by contact between animals of discharge from the eye or by flies.
“Treatment is problematic; it can be effective if done early and other cattle are not made worse. Is it worth getting them in at the risk of creating more close contact, dust and potential spreading of the disease?
“If there is a large percentage of a mob affected, yarding the animals and creating co-mingling is not a positive so it puts the pressure on detecting early cases.
“Patching is an essential component of treating pink eye as it protects against current and further UV radiation, enhances healing time, reduces spread to other animals and it marks the animal as treated.
“With mild pink eye, check and remove any foreign body such as grass seed or piece of hay, use an ointment or sub conjunctival injection (oil based pencillin and steroid) to reduce the bacterial infection and apply fly repellent.
“In severe pink eye, check and remove any foreign bodies, and use long-acting antibiotic and anti-inflammatory injection and protect the eye with a patch. Use a fly repellent and consider isolation.”
Dr Thomson said there was no controlled data supporting the use of alternative treatments such as kerosene, petrol and pink eye powder which exacerbate or induce further irritation to the eye.
-Kim Woods