Utilization of essential oils as an alternative to antibiotics to enhance the natural immuty is being used recently by veterinary professionals but there is little research that can support both productive and physiologic benefits of such practice. We conducted a trial with 61 lactating calves (1 week old) and grouped into treated animals with essential oils or control animals. Animals were sampled for blood haematological tests at 12, 32 and 54 days, as well as faeces for oocysts concentration. ADG and feedstuff intake were also measured. Administration of essential oils increased the ADG and trended to reduce the feedstuff intake and the parasitic load. However no differences were found between both groups in any of the haematological parameters studied. Results suggest that essential oils of the animal but there are no evidences that link it with type of boost in the natural immunity in the lactating calves.