Prevalence of bovine leukemia virus in Black and White cows with the different level of milk productive traits

The association study of BLV status (carrier, non-carrier) with the level of milk productive traits in Black and White cows of different lactation periods was performed. The blood samples were derived from the whole herd including 382 cows of fist lactation period, 253 cows of second lactation period and 197 cows of third lactation period. The presence of provirus form of BLV in blood leucocytes was detected by nested PCR using developed system. Based on results of PCR analysis the cows received BLV + or BLV - status. The increase of the number of cows with BLV + status from 28.5 per cent of fist lactation period cows to 36.1 per cent of third lactation period cows was observed. The significantly higher BLV prevalence (+9.0…+ 21.7 per cent) in fist lactation period cows with the «mean» (within X average±s) and «high» (more than X average+s) levels of milk productive traits (milk yield, fat content, milk fat and protein yield) comparing to «low» productive cows (less than X average-s) was observed. The data analysis in aspect of different milk productive traits indicated the higher differences between the groups differed in milk fat yield (18.3-21.7 per cent, p + status comparing to BLV - status was observed.