Understanding temporal and spatial distribution of intestinal nematodes of horses using faecal egg counts and DNA metabarcoding

This study reports the spatial and temporal distribution of ascarid and strongylid nematodes in Thoroughbred horses by age category across different climatic zones in Australia over an 18-month period. Faecal samples (n = 2046) from individual horses were analysed using the modified McMaster technique for faecal egg counts (FECs). Strongylids were identified using PCR-directed next-generation sequencing of the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA. Yearlings had the highest prevalence (82%) of strongyle eggs followed by weanlings (79%), foals (58%), wet mares (49%) and dry mares (46%). For Parascaris spp., foals had the highest prevalence (35%) followed by weanlings (21%) and yearlings (10%). The highest mean FECs for Parascaris spp. were observed in foals (525 eggs per gram [EPG] of faeces) while those for strongyles were in yearlings (962 EPG). Among horses that were classified as adults at the time of sampling, 77% (860 of 1119) of mares were low (i.e., < 250 EPG) strongyle egg-shedders. Mean strongyle FEC counts were highest in the Mediterranean (818 EPG) followed by summer (599 EPG), winter (442 EPG), and non-seasonal (413 EPG) rainfall zones. Twenty-six nematode species were detected, with Cylicostephanus longibursatus (26.5%), Cylicocyclus nassatus (23.7%) and Coronocyclus coronatus (20.5%) being the most frequently detected species. Their richness and relative abundance varied with horse age, season and climatic zone. In addition, Strongylus equinus and Triodontophorus spp. (T. brevicauda and T. serratus) were also detected. This comprehensive study elucidates spatial (climatic zone) and temporal (i.e., seasonal) trends in prevalence and burdens of intestinal nematodes in Australian horses using non-invasive conventional and molecular methods. The information presented in this study is crucial for developing integrated management strategies to control horse parasites in farmed horses.