Rewarm the calf by immersion in warm water (100°F). Remember that normal rectal temperature of the calf is 103°F. Make the depth of the water so that it covers the total calf. The feet of the calf will need to be tied, much as a calf roper would do. Cold calves tend not to struggle. Make sure you support the head. This can be done by putting a halter on the head and securing the lead rope snug enough to keep the head above water. You will also need a warm area so that the calf can get completely dry before returning to its dam.