Rotavirus, K99+ and coccidia were identified from feces of 10%, 13% and 37% of 300 selected dairy calves ⩽3 months of age, and from 26%, 36% and 45% of 42 Costa Rican dairy farms, respectively. Calf breeds were Holstein 68%, Jersey 27% and other breeds 5%. Median calf ages at identification of rotavirus, K99+ and coccidia were 14.5, 15, and 3 days, respectively. Differences between isolation rates for the wet and dry season were not statistically significant for any of the three agents. Prevalence of antibodies against infectious bovine rhinotracheitis and bovine parainfluenza-3 virus were 7% and 82%, respectively, for selected calves. Of calf sera tested for immunoglobulins, 9.5% were negative.
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