Calf diarrhea caused by bacterial infection has a bad effect on the dairy industry all over the world when calves are reared intensively. The pre-weaning mortality of dairy calves was estimated by the National Animal Health Monitoring System in the United States at 10.8% with diarrhea responsible for more than half of those deaths. Among these bacteria Eschirechia coli (E. coli) as “white scour”, Salmonella typhyimurium (S. typhimurium), Clostridium perfringens (C. Perfringens) and Staphylococcus aureus (St. aureus) are believed to be the major microbial causes diarrhea in calves. Antimicrobial agents are considered popular to fight it. Resistance to antimicrobial agents was frequently occurred in Salmonella species and E. coli particularly in pre-weaned dairy calves.