Epidemiology and Multidrug Resistance of Strongyle Nematodes in Ordos Merino Sheep
Background: Regular whole-flock treatments and long-term repeated use of similar anthelmintics has led to the development of anthelmintic resistance and widespread epidemic of sheep nematodiasis. The current work was carried out to understand the prevalence of gastrointestinal nematodes in Ordos merino sheep and to evaluate the efficacy of currently used anthelmintics. Results: A total of 4014 fresh fecal samples were collected from sheep from March 2017 to April 2019 and fecal nematode eggs
... al nematode eggs were qualitatively and quantitatively analyzed for understanding the prevalence of sheep nematodiasis. The anthelmintic efficacy of currently used drugs was evaluated in naturally infected sheep. The gastrointestinal nematode infection was serious in Ordos merino sheep. The infection rates of nematodes in three consecutive years were 84.3%, 36.9%, and 42.3%, respectively. The Hemonchus contortus and Nematodirus sp. were the dominantly infected species with the infection rates of 84.3% and 65.6% in 2017. Moreover, these species were acquired highly resistance to the Ivermectin, Doramectin, Albendazole and Levamisole. The percentages of FERC were 6.9%, 1.7%, 3.5% and 79.0%, respectively, following single administration. However, Nitroxynil and Closantel showed a strong anthelmintic efficacy on popular dominant species Haemonchus contortus and some other nematodes, while almost no effect on Nematodirus sp. Conclusions: The prevalence of gastrointestinal nematodes in Ordos merino sheep and their resistance to commonly used anthelmintics were comprehensively understood, and the high efficacy drugs on predominant species were screened out. The results will pay a good foundation for developing of reasonable drug use.