This is probably caused by cryptosporidia.The scours,hair loss,and age of the calf are dead give aways for this.Cryptosporidia is almost always present in the calves enviroment.Ingestion of one cell on day 1 can be as many as 1 million by day 8.There are no products that claim to treat crypto,however decoquinate (deccox) wil help control it .It must be added to the milk day and night for about 14 days.
Larry