EN
The aim of the work was to determine the frequency of prenatal infection with BLV and assessment of selected diagnostic methods. Blood and colostrum collected from 74 cows and 74 calves were taken before colostrum administration and 24 hours after feeding colostrum. The animals derived from the herds W and В infected with BLV in 90%. Serological examinations for antibodies against BLV were carried out by the AGID test and ELISA. On the W and В farms positive results were found in 10% and 13% of calves by means of the AGID and 15% and 22% by ELISA, respectively. The findings indicated that ELISA was much more useful compared with the AGID for serological examinations of new-borm calves. In addition, one should anticipate that prenatal infection with BLV constituted an essential epizootiological problem expressing the danger of virus spreading by calves housed together in the first six months of life i.e. when first serological tests took place.