In a series of three tests, a process of infection through the milk obtained from a cow infected with bovine leukemia virus was simulated in calves under natural conditions. The test on rabbits showed that their infection with bovine leukemia virus is possible through alimentary canal. Feeding rabbits with milk or milk with blood taken from the cow infected with bovine leukemia virus caused the following signs: antibodies to virus antigens in the serum and proviral DNA in the blood lymphocytes. Such infection of the rabbits after oral administration of milk obtained from the cow infected with bovine leukemia virus indicates the risk of infection for people. The minimum doses of proviral DNA were established. These doses cause infectious process after intravenous and oral administration of 3,6x10 7 copies and 2,7x 10 9 copies, respectively.

This work deals with the systematics and taxonomy of orthobunyaviruses, little-studied dangerous and new iruses Akabane, Aino, Schmallenberg, Cache Valley diseases, Oropouche fever. The significance of the reassortment mechanism of their origin and diversification is discussed.

The results of experimental infection of seronegative calves with three non-cytopathogenic (NCP) isolates of BVDV isolated from cattle with different clinical manifestations of the disease belonging to genotype 1 (subgenotype 1a, 1b and 1d) are presented. All tested isolates showed the virulence for seronegative calves 4 to 6 months of age. Belonging to biotype did not correlate with the ability of the virus to infect the lymphoid tissues and to induce leukopenia. All isolates of the virus led to "transiting" leukopenia (up to 2880-3800 kl/mm3) for 8-10 days after infection. Isolate cluster 1d was more virulent and caused the development of a mild respiratory syndrome and short-term diarrhea. The virulence was "strain-dependent".

Bovine viral diarrhea (BVD) is one of the greatest challenges for breeding and commercial livestock. It is characterized by lesions of the respiratory and gastrointestinal tract, abortion, infertility, immune deficiency, and persistence of the pathogen. In this work, a set of measures for the rehabilitation and prevention of BVD in cattle is described. It includes the data of the literature, guidance documents for the diagnosis and control of BVD adopted by OIE, EU countries, USA, as well as the results of this research.

From bone marrow (BM) and fatty tissue (FT) of cattle the authors isolated the cell populations with phenotype, similar to multipotent mesenchimal stem cells (MMSC). The comparative analysis was made for the properties and the features of isolated cell populations. It was established, that cattle MMSC, isolated from BM and FT, capable to form the cells of bone and fatty tissues at the cultivation in induction media in vitro. The obtained results suggested that cattle BM and FT are important source of MMSC, which can be used in agricultural and food biotechnology, veterinary, virology.