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Pink eye in cattle is usually a bacterial infection. Bovine pink eye can also negatively impact a cow's ability to give milk, and can cause weight loss, starvation, blindness, and injury. It is sually caused by infection of the bacterium Moraxella bovis. Pink eye in cattle can cause sensitivity to light, corneal ulceration, and corneal rupture.
Many strains of the Moxarella bovis bacterium responsible for pink eye in cattle exist, and there is not currently a vaccine to protect against the infection. The toxins that M. bovis produces are generally considered responsible for the severe damage that pink eye can cause to the membranes of cows' eyes.
Some conditions can make cattle more likely to contract pink eye. Any foreign object that irritates the eye can make cattle more vulnerable to this disease. Bright light and dusty conditions can also contribute to the develop of severe bovine pink eye. Flies are often implicated in the development of bovine pink eye infections, since they can spread the M. bovis bacteria from animal to animal.
The first symptom of pink eye in cattle is generally an increase in eye secretions. Tears may flow freely in animals exhibiting the first signs of bovine pink eye. Pink eye can also make the animal's eyes more sensitive to light, so cows with this infection may begin to squint or blink excessively. The conjunctiva, or membranes of the eye, usually become inflamed.
As the disease progresses, ulcers may form on the cornea of the eye. Ulcers usually appear as white spots on the surface of the eye. In milder cases of infection, the ulcer may begin to heal on its own. In more severe cases, the ulcer may expand in size, eventually causing corneal rupture. If the cornea ruptures, the fluid of the inner eye can leak out, and the remaining eye tissue can collapse into the eye socket.
In most cases, cattle recover from pink eye without permanent vision loss. Recovery usually becomes evident in the final stage of the disease, as the surface of the eye becomes excessively red, then bluish and opaque, and then, finally, returns to normal. About two percent of cattle afflicted with pink eye remain permanently and completely blind in the affected eye. If scarring of the cornea occurs, then a bluish area may remain visible in the center of the eye after the animal recovers. Complete recovery from pink eye in cattle takes between three and five weeks in most cases.