RESUMO
Bovine babesiosis is an infectious protozoan disease and causes significant economic losses in terms of production loss and mortality. The genus Babesia belongs to the family Babesiidae order piroplasmida and is transmitted by ticks globally. The signs of disease are particularly prominent in old or immuno-compromised animals. The spleen plays a vital role in defence against hemoparasites like Babesia. A young cross-bred cow calf of about 3 months of age was splenectomised to propagate Babesia in vivo experimentally. Prior to splenectomy, the calf was examined through microscopy and PCR analysis and was found negative for any kind of piroplasms including Babesia. The calf was completely splenectomised, but the calf was naturally infected during its postoperative period. The calf expired after naturally acquiring Babesia bigemina and Theileria annulata during the 11 th day of postoperative period owing to increased parasitaemia, exhibiting typical mixed parasitic infection stigmata e.g. reddish urine, elevated temperature up to 41.38°C. This study concluded that complete splenectomy along with dexamethasone administration in the postop period caused exceptional increase in parasitaemia. This parasitaemia couldn't be countered by any symptomatic treatment because of the absence of spleen and greatly reduced immunity of the animal.