Caprine Roundworm Nematode Resistance to Macrocyclic Lactones in Northeastern Thailand

Roundworm nematodes are a significant problem in goat meat farming worldwide. These parasites can cause production losses, reduce feed efficiency and compromise animal health and welfare. Macrocyclic lactones (MLs) are common anthelmintic drugs to treat roundworm nematode infection in livestock. The objective of study was to detect roundworm resistance to MLs in meat goats in Northeast Thailand. One hundred and nineteen goats from 6 herds were studied from June to December 2022. Each herd was randomly allocated to control (n=21), epinomectin (n=34), ivermectin (n=40) and moxidectin (n=24) groups. Anthelmintic resistance (AR) was assessed based on the Fecal Egg Count Reduction Test (FECRT) and larva culture at pre-treatment (D0) and 14 days post-treatment (D14). Prevalence of Strongyle nematodes and Trichuris spp. infection was 100% (6/6 herd), and 66.7% (4/6 herd), respectively. The number of Strongyle eggs was significantly reduced in the eprinomectin group (p < 0.01). In contrast, the ivermectin group was significantly increased (p < 0.01). The prevalence of ML resistance of Strongyle nematodes and Trichuris spp. was 83.3% (5/6 herd) and 25.0% (1/4 herd), respectively. The dominant larva was Haemonchus contortus at pre- and post-treatment in every herd. This study demonstrated the presence of ML resistant Strongyle nematodes as H. contortus and Trichuris spp. in this area. To reduce ML resistance it can be useful to use drugs in combination or rotate MLs with other classes of anthelmintics or in targeted treatment programs and integrated parasite management strategies. Consequently, the efficacy of anthelmintic drugs in small ruminants needs to be monitored and surveilled in this area.