Abstract: [Objective] To investigate the infection status of Cryptosporidium spp. and Giardia duodenalis in grazing Yanqi horse populations in the Bayinbuluke Grassland. [Methods] A total of 103 non-diarrheic fecal samples were randomly collected from grazing Yanqi horses. Nested PCR combined with gene sequencing was used for accurate identification and genotyping of Cryptosporidium spp. and G.duodenalis, and phylogenetic trees were constructed to analyze the genetic evolutionary relationships of the pathogens. [Results] Based on PCR detection of the Cryptosporidium spp. SSU rRNA gene fragment, the positive rate of Cryptosporidium spp. in Yanqi horses was 2.91% （3/103）, which were identified as Cryptosporidium hominis （n=2） and Cryptosporidium bovis （n=1）. Further sequence analysis of the gp60 gene fragment showed that the detected C. hominis isolates were all of the IkA16G1 subtype （n=2）. PCR detection targeting the G. duodenalis SSU rRNA gene fragment revealed a positive rate of 1.94% （2/103） in Yanqi horse population, and all were identified as Assemblage B （n=2）. Phylogenetic analysis showed that the Cryptosporidium spp. and subtype sequences obtained in this study clustered with known sequences from multiple hosts, without obvious genetic isolation characteristics; meanwhile, the G. duodenalis Assemblage B sequences formed a monophyletic group with equine- and human-derived sequences, suggesting potential zoonotic risk. [Conclusion] The infection rates of Cryptosporidium spp. and G. duodenalis in grazing Yanqi horses in the Bayinbuluke Grassland were at relatively low levels, and systematic and continuous monitoring should be promoted in the future.

Key words: Yanqi horse, Cryptosporidium spp., Giardia duodenalis, Bayinbuluke grassland