Which disease is indicated by symptoms such as rigid ears, wide eyes, and drawn-back lips in a cow?

The symptoms described—rigid ears, wide eyes, and drawn-back lips—are classic signs of tetanus in cattle. Tetanus is caused by the neurotoxin produced by the bacterium Clostridium tetani, which affects the nervous system and leads to muscle stiffness and spasms. The facial muscles, including those that control the lips, can be significantly affected, resulting in a characteristic appearance known as "sardonic grin."

Additionally, the rigidity of the ears and the wide-eyed stare are indicative of the heightened state of alertness and rigidity associated with this condition. In the case of tetanus, the rigidity is due to continuous stimulation of the muscles, leading to sustained contractions.

While other diseases have their own set of symptoms, none align closely with the specific combination of signs presented in this question. For instance, botulism is characterized by a flaccid paralysis rather than rigidity; mad cow disease features neurological signs but usually presents with different behavioral changes; and foot and mouth disease primarily manifests with oral lesions and lameness rather than the specific facial muscular rigidity described.