Efficacy of moxidectin and an ivermectin-praziquantel combination against ascarids, strongyles, and tapeworms in Thoroughbred yearlings in field tests on a farm in Central Kentucky in 2016

Field tests were performed on Thoroughbred yearlings (n=143), evaluating efficacy of moxidectin (MOX) against ascarids and strongyles and the efficacy of an ivermectin (IVM)-praziquantel (PRAZ) combination against those nematodes and tapeworms on a farm in Central Kentucky. The study was started on March 1, 2016 and completed on August 23, 2016. Fecal samples were collected from yearlings every two weeks for counts of ascarid and strongyle eggs per gram of feces (EPGs) and for determining the presence of tapeworm eggs. MOX was given to 88 yearlings on March 1; 55 yearlings were nontreated controls on this date but were treated two weeks later with MOX. On June 15, 2016, all yearlings (n=87) remaining on the farm were treated with IVM-PRAZ combination. Ascarids were present in low numbers for MOX-treated horses, and the drug had virtually no effect. The low number of ascarid infected horses before any treatment during the study was most likely due to age related immunity. Efficacy against strongyles was alike for both MOX and the IVM- PRAZ combination. At two weeks post-treatment, strongyle EPG values were reduced over 90%, started increasing at four weeks post-treatment, and returned to near pre-treatment values at six weeks post-treatment. Tapeworm efficacy of the IVM-PRAZ treatment was 96% at two weeks and was maintained for the entire ten-week post-treatment examination period.