If you have nothing else handy, use some Immodium like people use for diahrrea. Give the calf 2 tablets. It will "stop him up" just to get him to stop dehydrating as you work on getting electrolytes in him and getting him feeling a little better. If he is not shooting it out the back end as fast as it goes in the front, you can then work on treating the scours. I like Immodium better than using something like Kaopectate, because they will take a couple of little pills easier than something that is thick and tastes crappy. Hereford2 gave you good advice about the feeding and alternating the electrolytes and milk. I will sometimes not feed any milk for 24 hours, just electrolytes, to get them rehydrated.