The aim of the study is to investigate if treatment of calf pens with slaked lime will prevent spread of C. parvum and improve the calf health in herds with C. parvum associated diarrhea problems. Diarrhea is common in young dairy calves in Sweden and is often caused by C. parvum. The parasite is resistant to all recommended disinfectants making it particularly difficult to control. We have shown that slaked lime decreases the viability of C. parvum in the laboratory. When slaked lime treatment of the calf pens was used as a complement to the standard cleaning procedures in two herds with long-lasting cryptosporidosis problems the farmers reported a lower incidence and less severe diarrhea in the calves. This indicates that slaked lime treatment might be an effective control measure in cattle herds. However, before the method can be recommended the efficacy has to be confirmed in a controlled study.