FEATURES OF DIAGNOSIS OF NECROBACTERIOSIS OF COWS BY PCR-RFLP

Abstract

Molecular genetic markers can detect polymorphism at the DNA level. This feature determines the possibility of their widespread use in genetics and breeding. Alleles of the BoLA-DRB3 gene (exon 2) can act as such markers if a statically significant association between the disease and the allele is established. The presence of such DNA markers in the genotype of animals makes it possible to judge the likelihood of disease in postnatal ontogenesis immediately after the birth of a heifer, based on which we can conclude about the conditions of further use of the animal in the main herd. According to the results of studying the polymorphism of the BoLA-DRB3 gene in cows of the Ukrainian black and white dairy breed resistant and susceptible to necrobacteriosis, four "informative" alleles were revealed. Two of them *03 and *22 are associated with resistance, and the other two - *16 and *23 with susceptibility to necrobacteriosis. The presence of these alleles in the genotype of the animal is determined by testing performed by PCR-RFLP. The method is time consuming, labor intensive and costly. To simplify it, the following technique is proposed. Restriction fragments of alleles *03, *16, *22 and *23 for endocluases RsaI, XhoII and HaeIII have the following DNA patterns: bbb, jbd, mba and nba. Due to the peculiarity of the restriction fragments, which is that endonuclease XhoII reveals in these alleles only one pattern b with length of 284 bp, the process of determining informative alleles can be simplified. Isolation of DNA from blood samples and amplification of a fragment of the BoLA-DRB3.2 gene with a size of 284 bp is carried out according to the established technique. Next, the restriction of the fragment by endonuclease XhoII and sampling having a pattern b. Selected samples are treated with RsaI endonuclease and only those with patterns b, j, m and n remain. The next step is to restrict the selected samples with HaeIII endonuclease and select heifers with bbb (*03) and nba (*23) genotypes. After the first restriction, blood samples without pattern b are eliminated from the experimental sample; after the second – two alleles with patterns RsaI + XhoII jb (*16) and mb (*22) are unambiguously determined, after the third – genotypes bbb and nba, which correspond to alleles *03 and *23. In total, only 75% of blood samples are typed, which reduces the material consumption, time and cost of work to identify heifers genetically susceptible (resistant) to necrobacteriosis.