Formation of the herd free from enzootic bovine leukosis on the basis of PCR-diagnostics of calves

The bovine leukosis virus (BLV) causes a disease that results in reduced quality of life for animals and economic losses for businesses. The prevalence of BLV is high both globally and in the Russian Federation. Therefore, the question of the methods of controlling this disease, including for the formation of a healthy herd, becomes relevant. The purpose of the study is to form a herd of cattle free from BLV infection on the example of the work of a farm in the Novosibirsk region. Cattle blood samples were collected in a total of 434 samples from the calves not more than 3 months of age from March to August 2023. The phenol-chloroform method was used to isolate total DNA from peripheral blood of cattle. A commercial test system RealBest-Vet DNA of cattle leukosis virus V-5441 (VectorBest, Russian Federation) and a self-developed test system were used for PCR-diagnostics of the samples for the presence of BLV. A portion of the positive samples were sequenced by Sanger sequencing using the commercial BigDye Terminator v3.1 kit. Out of 434 samples, 44 samples were positive for the presence of BLV. For the first 15 samples out of 44, amplification of the env BLV gene fragment was performed followed by sequencing: 11 virus samples belonged to genotype 4, 4 samples belonged to genotype 7. Based on the obtained veterinary epidemiological data, a set of measures aimed at formation of a healthy herd was started: improvement of qualification of the enterprise employees, timely and qualitative diagnostics of animals, isolation, tagging and transfer of calves with negative test results to the base of healthy animals, repeated blood sampling in 3–6 months to confirm the results of the previous testing. The farm has adopted a plan of stage-by-stage modernization, including creation of conditions for separate housing of cattle tested for leukosis; a set of requirements for the work of personnel, rules of disinfection and the use of tools, etc. have been developed. 

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