The transmission of Cryptosporidium parvum between dams and their respective calves was studied. For this purpose, fecal specimens taken from the rectum of preparturient, parturient, and postparturient dams were analyzed for C. parvum oocysts. Fecal specimens were taken from the newborn calf 4 hr after birth. Because the environment can be a source of contamination to the animals, specimens taken from inside and outside the barn were analyzed. The sucrose concentration method together with the Zielh–Nielsen acid-fast staining method were employed to increase the chances of oocyst detection. We are reporting that at parturition, the dams shed a higher number of oocysts by comparison to the preparturient and postparturient periods. Neonates acquire the infection at birth mainly because of the high number of oocysts shed by the dams at parturition. The management practice of moving calves 4 hr after birth away from the dams and the barn reduces the number of clinical cases because they are no longer in contact with an environment that is highly contaminated. We hypothesize that the increase in the number of oocysts sheds by dams at parturition might be due to a depression of the T helper 1-type of immune response during that period.

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