2.1 Ethics statement
This study was conducted according to the animal welfare guidelines of the World Organization for Animal Health, and animal sampling was carried out in strict accordance with guidelines established by the Ethics of Animal Experiments of Northwest A&F University, Yangling, China. All the protocols were approved by this committee (Permit Number: 2014BAD23B11). The field study did not involve endangered or protected species. No specific permissions were required for the collection of samples because the samples were collected from public areas or non-protected areas.