An estimated 56% of health problems in early life relate to diarrhea, making it a number one health issue for newborn calves. It accounts for 52.2% of mortality of unweaned calves, and is also a major cause of poor growth, increased labour requirements and increased costs (www.biomin.net source). In severe cases, an outbreak of scour can kill up to a third of affected calves. The cost per sick calf is estimated at 44 £ (excluding labour). Outbreaks of infection causing calf diarrhea are often rapid and multifactorial in nature. Major enteric pathogens known to cause calf diarrhea are protozoan parasites (Cryptosporidium parvum), viruses (bovine rotavirus, bovine coronavirus), and bacteria (E. Coli K99). Rapid in vitro diagnostic tests help to identify the infectious agent(s) responsible for the disease. Early detection is an important issue since the large amount of parasites excreted by young calves quickly contaminate the congeners. Depending of the European country considered, epidemiological surveys indicated that Cryptosporidium is the first or second leading cause responsible for calf diarrhea with prevalence almost equivalent to that of rotavirus infection. In a recent research program performed in France (Britany and Normandy) on Holstein and Charolais calves we observed using the Speed-V-Diar Kit that Cryptosporidium was by far the most prevalent infectious agent. Cryptosporidiosis is also a major One-health problem with severe health consequences for very young, malnourished children living in endemic areas and for immunocompromised individuals. Cryptosporidia are particularly resistant parasites in the external environment where they can survive more than a year. In practice, for a good disinfection (soils, walls and equipment in contact with calves),