Polymerase chain reaction in diagnostics of latent and persistent forms of infectious cattle diseases

PCR was carried out as a diagnosis of biological and pathological material from cattle, from 17 farms located in the Ural region. We studied biological samples from cows with a decreased milkproduction against the background of the absence of clinical symptoms of infectious diseases. Samples of organs from aborted calves and from cattle with suspected infections, negative for ELISA and bacteriological examinations were analyzed. For the period 2016–2019 we examined 830 samples by PCR to identify DNA of BVD, BHV 1, Chlamydophila abortus, Chlamydophila pecorum, Mycoplasma spp., M. bovis. Genetic material of these pathogens has been identified in 5.4% of the biosamples. In 1.0% of the biological samples (placenta from aborted cows, organs from aborted fetuses), a specific DNA fragment of BHV 1 was detected. Results confirmed the presence of a persistent genital form of infectious rhinotracheitis in the examined animals. BVD DNA was isolated in 1.0% of the biological samples of stud bulls’ semen, placenta from aborted cows and organs from aborted fetuses, which made it possible to identify virus-bearing animals with a latent form of BVD infection. Mycoplasma spp. was diagnosed in 2.4% of the cases: 4 samples of M. bovis were found in the cows’ vaginal mucosa, which is a sign of a chronic inflammatory disease of the reproductive organs. C. pecorum was diagnosed in lavages of the cows’ cervical canal and in 1.0% of lavages of newborn calves’ conjunctiva. The PCR method allowed to identify the etiological agent in latent and persistent infections. Results of these studies made it possible to timely initiate a treatment and take prophylactic measures in cattle populations of the examined farms