Analyzed the rate of somatic mutation of peripheral blood lymphocytes in horse breeds: Russian trotting, Holstein, novooleksandrovsky carthorse, Ukrainian horse. Ukrainian riding horses breed revealed the highest level of aneuploidy. Mares of novooleksandrovskoy carthorse breeds have the highest frequency of the asynchronous cleavage centromeric regions of chromosomes. The lowest level of quantitative and structural genomes abnormalities of somatic cells were found in Holsteins horses. Found an inverse relationship between the frequency of cells with micronuclei and milk productivity of mares Novoaleksandrovskaya carthorse breed.