Abstract
Salmonella abortion of mares takes a leading place in the in factious pathology of horses and leads to the abortion of pregnant mares and infected stallions become salmonella carriers. The disease with salmonella abortion manifests itself in the last months of pregnancy, maybe-during the mass foal of mares-in the spring. The article results obtained of studies on the biological properties and genetic characteristics of the attenuated strain of Salmonella abortus-equi E-841 compared with the control virulent strain of Salmonella Salmonella abortus-equi 7/1. These strains after inoculation on nutrient media retained their viability and had typical cultural-morphological, tinctorial and serological properties. When determining drug resistance, it showed resistance to rifampicin. As a result of studying the biochemical properties, it was found that the strain does not ferment urea, does not decompose gelatin and does not form indole, does not produce hydrogen sulfide. When determining the antigenic structure, it was shown that the attenuated strain is agglutinated in RA on glass with polyvalent and monoreceptor sera. The presence of mutations was determined by sequencing amplification fragments of the rpoB and rpsL genes. In the attenuated salmonella strain, mutations were found in the nucleotide sequences of fragments of the rpoB and rpsL genomes that cause antibiotic resistance and reduce the virulence of the strain, preventing the transformation of the strain into a virulent prototype of salmonella.