[The complex etiology of epidemic diseases in calves on large-capacity farms and their clinical and epizootic characteristics].

It is not easy to exactly diagnose the etiology of the mass infections of new-born calves on large farms where considerable losses are suffered. On the basis of the complex epizootological, clinical and laboratory examination in four large calf-rearing facilities, rotaviruses, coronaviruses, the infectious bovine rhinotracheitis (IBR) virus and the bovine viral diarrhoea (BVD) virus, and in some cases also the enteropathogenic E. coli, were found to be etiologically involved in the mass rise of diarrhoea, complicated by respiratory symptoms already during the first days after birth. The clinical picture of the disease, therapeutically difficult and reminding of "pneumoenteritis", has often been observed in stocks where, in addition to rotaviruses and coronaviruses in the faeces, the IBR or BVD viruses (sometimes both at the same time) were detected and identified in the respiratory and enteral tract. The serological examination of a higher number of animals in the stocks of calves under study confirmed the considerable rate of spreading of all the four viruses in the cattle population and, at the same time, demonstrated the very unfavourable immunological profile of the herds. The high percentage of animals low in antibody titres and the serologically negative animals constitute the infection-sensitive part of population in the affected herds. With the high culling rate and with the open herd turnover it is impossible to reach the required immunity through natural disinfection. Loss-free rearing of healthy calves will be achieved on the basis of a well-oriented vaccination programme with a good combination of inoculants.