Abstract: Eimeria bovis, Eimeria zuernii, Eimeria ellipsoidalis, Eimeria auburnensis, Eimeria canadensis and Eimeria alabamensis were identified on different dairy farms in Uruguay. The most prevalent species were E. bovis and E. zuernii, which were mainly found in the feces of calves with diarrhea. The dynamics of oocyst excretion were evaluated via the weekly determination of oocysts per gram (OPG) values in fecal samples from 97 calves over seven months. Three groups of calves were formed according to their age in days:Group 1 (1?20 days old), Group 2 (21?40 days old) and Group 3 (41?65 days old). In Group 1, the median OPG was zero, and the maximum OPG was 1,680. In Group 2, the median OPG was between zero and 8,240, and the maximum OPG was 428,800. In Group 3, the median OPG was between zero and 220, and the maximum OPG was 16,000. For the evaluation of the relationship between OPG and age group, a proportional odds model was built. Two samples from 60 bovines evaluated in Group 2 and in Group 3 were selected. OPG was categorized as negative, moderate (lower than or equal to 4,000) or high (greater than 4,000). Calves of Group 2 (21?40 days old) were significantly (p