Replace lost body fluid and electrolytes in large enough quantity often enough that loss does not become profound. Calf will suck electrolyte solution from a bottle Leave calf on milk and add several 2 quart electrolyte feedings per day until scouring slows. Even though nutrient absorption is incomplete, the calf needs what it can get from the milk. Old recommendation to take calf off of milk is wrong. These solutions contain high levels of glucose to provide energy and other components to promote absorption.
Calf needs to be moved to a warm area where it can be monitored.
Take calf to veterinary clinic immediately. Keep up with ongoing loss of 1 to 4 Liter per day in the diarrhea. One of the signs that enough is being given is that more normal large volume urination resumes. Enteropathogenic - specific strains. A most common cause of calf death.