Abstract: Gastrointestinal nematode (GIN) infection in sheep has been recognized globally as a major problem challenginganimal health and production. The objective of this study is to use a molecular diagnosis of the prevalence forgastrointestinal nematode (GIN) dominant species of Kazakh sheep and its hybrid (Kazakh × Texel). The internatranscribed spacer 2 (ITS-2) sequences of ribosomal DNA (rDNA) were used as the target sequence. In the studythree dominant species of nematodes, namely Haemonchus contortus, Trichostrongylus spp., and Teladorsagia(Ostertagia) circumcincta from the Kazakh sheep and the F1 and F2 generations of Texel × Kazakh sheep hybridswere subjected to molecular identification and phylogenetic analysis. The fecal and single larva genomic DNA were extracted and amplifed by PCR using specific primers to determine the infection rate of the three nematodespecies. In addition, the PCR products were sequenced and analyzed using bioinformatics methods to construct aphylogenetic tree. The results showed that all the three species had their ITS-2 specific amplified. According tothe sequence homology analysis of PCR products, the results showed a high homology (above 98.5% homology) with H. contortus, Trichostrongylus spp., T. circumcinctaITS-2 sequences in GenBank, Phylogenetic analysisshowed that the ITS-2 sequences of the three species were on the same branch as the ITS-2 sequences of the samespecies in NCBI. And on different branches from those of the ITS-2 sequences of different families, genera and species. Sequences carried out on three species from different samples showed a close relationship and littlegenetic difference in phylogenetic tree. The infection rates based on fecal DNA were 35.59, 25.55, and 11.24% for H. contortus, Trichostrongylus spp., and T. circumcincta, respectively. While the infection rates based on larvaDNA, were 24.07, 18.89, and 13.26% for H, contortus, Trichostrongylus spp., and T. circumcincta, respectively. Theseasonal prevalence of the three dominant species in spring was significantly higher than that in autumn andwinter. And there was no significant difference between Kazakh, Fl and F2 sheep considering the infection rateof the studied three species of nematodes, This study provides valuable molecular approaches for epidemiological surveillance and for assisting in the control of Nematodirus infection in sheep.
Keywords: Kazakh sheep, Gastrointestinal nematodes, Molecular epidemiology, Phylogenesis, The second internal transcribed spacer of ribosomal DNA
