There may be a couple of causes for the enlarged scrotum. The calf may have been stepped on butted by an older calf and may have injured one or both of the testicles. The other cause may be a hernia. When the testicles decend down from the body cavity prior to birth, they pass through the inguinal canal. After the testicles pass through the canal, the canal narrows in size. If the canal remained open, then there may be other tissue that has migrated into the scrotum. If the condition appears painful or if it doesn’t resolve, then have it examined by a veterinarian. Don’t castrate the calf while the swelling exists.