Hyperimmune anti-Cryptosporidium parvum ovine colostral whey (HOCW) was tested to determine whether it conferred passive immunity to newborn NMRI mice. Three HOCWs (groups IV–VI), 2 nonimmune colostral wheys (groups II and III), and PBS (group I) were administered once (experiment A) and 3 times (experiment B) daily from −1 to 15 days postinfection (PI). Mice in groups I–VI were inoculated with 5 × 10⁵ oocysts (day 0 PI), and group VII mice acted as controls. The percentage and intensity of infection were measured at 6, 9, 12, and 16 days PI. In experiment A, HOCW did not reduce significantly the percentage and intensity of infection except for mice in group VI treated with HOCW with the highest titers of anti-C. parvum antibodies. In contrast, no infection was detected in between 18.7 and 62.5% of the mice in groups IV–VI in experiment B. Furthermore, in these groups, the intensity of the infection decreased significantly, ranging from 83.5 to 97.4%. Thus, HOCW did not completely avoid infection, but a high level of protection was observed, being proportional to the titer of specific antibodies and the amount of whey administered orally. Finally, group VII showed no presence of oocysts.