Rabies classically has a cow/bull/calf which is unable to swallow so has drool hanging from it's jaw. A cow/calf will also roar with a bull's voice since there is laryngeal paralysis. They can also show as a migrating lameness, a downer, a stupid animal,aggressive...but all I've ever seen have been easy to recognize vs milk fever/calcium deficiency. Rabies is only diagnosed from brain tissue definitively--either inclusions in the neurons or by mouse innoculation test.
Calcium deficiency generally only occurs around calving time. It is most common in Jerseys, other dairy breeds less common, beef breeds uncommon, but possible. They start with a slight weakness, a wobble, which will progress to being unable to rise, and will progress to coma and death if left untreated. A classical sign of it is the eyelids will "snap" when the eye is menaced. The heart will become softer and softer and very difficult to hear. Treatment is IV calcium containing solution--often with dextrose, magnesium and/or phosphorus; sometimes all that's needed is oral calcium in a gel if caught early, often with subcutaneous calcium borogluconate with either treatment. A blood test will definitively diagnose the problem.
