These animals then serve as a source for continued infection of the rest of the herd. Eyes affected with foreign matter will not heal until the foreign matter is removed. Blowing dust and ultraviolet radiation from sunlight may cause irritation to initiate a pinkeye infection in a herd, and if face flies are present this can result in an outbreak. Pinkeye usually occurs in July and August when conditions cause cattle to be most susceptible to the infection. Signs of the infection include wetness of the face due to excess tearing from affected eyes, squinting of the eyelid, reddening of the conjunctiva and, in advanced stages, ulceration of the cornea which results in a discoloration or loss of the cornea.
Commercial vaccines are available for preventing pinkeye.
Insecticide eartags have been shown to be of benefit and dust bags and feed-through products that control face fly larva should also be considered. Clipping old tall pasture and controlling dust will also aid in reducing eye injury. Treatment should include protection of the eye and a localized anti-bacterial that can act against the M. bovis. An eye patch applied with adhesive usually works well. Patches are also available commercially.