Prevalence of anthelmintic resistance of gastrointestinal nematodes in Lithuanian sheep farms

The rapid emergence of anthelmintic resistance (AR) among gastrointestinal nematodes (GIN) in Europe, particularly to benzimidazoles (BZ), levamisole (LEV), and macrocyclic lactones (ML), presents a growing challenge to sheep farming. This study aimed to assess the prevalence of resistance to BZ, IVM, and LEV in Lithuanian sheep farms. <i>In vitro</i> micro-agar larval development tests (MALDT), recognized as the most efficient <i>in vitro</i> method for large-scale epidemiological studies, were used. The research was conducted from 2021 to 2022 across 38 sheep farms throughout Lithuania. Findings indicate widespread resistance to IVM (47.4 %) and BZ (39.5 %), while LEV resistance was not detected. Multidrug resistance (MDR) to both IVM and BZ was found in 28.9 % of farms. <i>Trichostrongylus</i>, <i>Teladorsagia</i>, and <i>Haemonchus</i> were identified as resistant species. Our results reveal a lower prevalence of AR compared to previous studies, highlighting the critical importance of randomized sampling. The study underscores the need for strategic anthelmintic management and enhanced cooperation among researchers, veterinarians, and farmers to mitigate the spread of AR in Lithuanian sheep farms.