Influence of Oregano essential oil (OEO) on prevalence and oocyst shedding dynamics of naturally acquired Eimeria spp. infection in replacement dairy heifers

The administration of oregano essential oil (OEO) was tested in a dairy farm (Piacenza, Italy) with a history of sporadic cases of clinical coccidiosis in order to evaluate its influence on infection prevalence and oocyst excretion pattern in calves and replacement dairy heifers. Animals were recruited at 1 month of age and allocated to two groups of 25 animals, experimental (E) and control (C). OEO was added at a concentration of 100 ppm to the feedstuff administered to group E. Prevalence of infection and the number of oocysts per gram of feces (OPG) was evaluated monthly from 30 days of life (d30) till d150, with one extra sampling at d45, for a total of 6 time points. No significant differences were observed regarding the prevalence of infection between the two groups (83% general prevalence, 93% in group E, 72% in group C) although slightly higher prevalence was seen for Eimeria bovis and Eimeria alabamensis in group C, while the opposite was seen for Eimeria zuernii. OEO addition to the diet did not have any effect on the course of coccidial infections in calves and replacement dairy heifers. Other variables, in particular data on growth and production, should likely be tested before ruling out the potential role of OEO, alone or in combination with other control measures, to reduce infection pressure and therefore to improve animal welfare and performance.