Coprological and Molecular Analyses of Ruminant Farms in Québec, Canada, Show a Variable Efficacy of Ivermectin Against Gastro-Intestinal Nematodes

Gastro-intestinal nematodes (GINs) are still of great concern in grazing ruminants, such as camelids, ovines and caprines, affecting animal health and productivity. This is mainly due to the development of anthelmintic resistance (AR) to the compounds used long term, without much evaluation on their efficacy, including ivermectin (IVM), the most used anthelmintic drug in livestock. The aims of this study were to determine the efficacy of IVM and identify which GIN species are affecting different ruminant farms in Quebec (QC), Canada. Firstly, we collected fecal samples from six farms with different ruminant species (camelids, goats and sheep) before and after IVM treatment when applicable, analyzing them by Fecal Egg Count (FEC) and further assessments on IVM efficacy through the Fecal Egg Count Reduction Test (FECRT). In addition, molecular analyses were conducted using PCR, targeting the ITS-2 and COX-1 genes to identify GIN species. FECRT was applied only for three farms, showing that variable results with optimal efficacy (ranging from 95.5-100%) were obtained in only one farm, whereas on the other two farms, FECRT exhibited reduced efficacy, suggesting the development of IVM resistance. Among the GIN species found, <i>Haemonchus contortus</i> and <i>Trichostrongylus vitrinus</i> were identified in most of the farms, being present in sheep, goat, llama and alpaca farms, whereas <i>Teladorsagia circumcincta</i> was identified only in sheep and llama samples from four farms but not in alpaca samples. <i>Trichostrongylus axei</i> and <i>Chabertia ovina</i> were present in two farms (sheep and sheep and llamas). <i>Oesophagostomum venulosum</i> was detected in one sheep and one alpaca farm. Only one sheep farm was positive for <i>Trichostrongylus colubriformis</i> and <i>Cooperia curticei</i>. Also, <i>Nematodirus</i> spp. and <i>Trichuris</i> spp. were found in four farms, including sheep and camelids. In addition, three other species were found in camelids, including <i>Camelostrongylus mentulatus</i> (only in the llama samples), whereas <i>Lamanema chavezi</i> and <i>Marshallagia marshalli</i> were identified in one alpaca farm. Therefore, our work reports evidence of an uneven efficacy of IVM against GINs from ruminant farms, including the most likely emergence of IVM resistance. The diversity of GIN species found in ruminant farms in QC along with the inconsistent IVM efficacy are helpful information for veterinarians and animal producers in setting an optimal parasite management programs, including the proper use of IVM and alternative anthelmintic drugs to control these pathogens in grazing livestock.