Calf scours can occur from an infection or from the consumption of a large amount of milk (aka milk scours). Watching calves to see how they act can help determine the potential cause of scours and what if any treatment may be needed.
Calves experiencing milk scours will have white, loose manure, but will be active and look normal. No treatment should be needed in these cases.
However, scours caused from an infection (e.g., rotavirus, coronavirus, E. coli, etc.) can result in calves that are lethargic and dehydrated. These calves will likely need fluids and other supportive care.