Cryptosporidiosis, caused by the apicomplexan parasite Cryptosporidium parvum, is a moderate-to-severe diarrheal disease, now recognized as one of the leading causes of morbidity and mortality in livestock globally and in humans living in resource-limited parts of the world, particularly those with AIDS or who are malnourished. This recognition has fueled efforts for the discovery of effective therapeutics. While recent progress in drug discovery has been encouraging, there are presently no acceptably effective parasite-specific drugs for the disease. The urgent need for new drug discovery or drug repurposing has also increased the need for refined animal models of clinical disease for therapeutic efficacy evaluation. Here, we describe an acute model of cryptosporidiosis using newborn calves to evaluate well-defined clinical and parasitological parameter outcomes, including effect on diarrhea severity and duration, oocyst numbers produced, and multiple measures of clinical health. The model is highly reproducible and provides unequivocal direct measures of treatment efficacy on diarrhea severity and parasite replication.