Date of Graduation


Document Type


Degree Name

Master of Science in Animal Science (MS)

Degree Level



Animal Science


Tom Yazwinski

Committee Member

Jeremy Powell

Second Committee Member

Nancy Jack


Biological sciences, Horses, Parasites, Selective treatment, Treatments


Parasite control is an important aspect of health management of horses, particularly the control of gastrointestinal (GI) parasites. Recently, treatment recommendations have involved selective use of anthelmintics in horses with fecal egg counts (FEC) greater than a specified threshold. The objectives of this study were; (1) to determine the prevalence of helminths in our area by egg and L3 determinations, (2) to determine if certain horses maintained low FEC, therefore eliminating the need to treat them on a year-round basis and (3) to determine the effectiveness of four common treatments (moxidectin, ivermectin (pioneer and generic), fenbendazole and pyrantel tartrate) via a standardized fecal egg count reduction (FECR) test. Fecal samples were collected from 226 horses at 14 different farms with a total of 933 fecal samples and 259 coprocultures evaluated over eight months. A treatment threshold of FEC > 200 eggs per gram (EPG) was used and horses were sampled once, twice, or three times over the course of the study. Of the 933 fecals analyzed, 303 had an EPG of zero, 407 were < 200 EPG, and 223 were >200 EPG. There were 37 samples that contained eggs other than Strongyle-type eggs and at least one of the three major large strongyle species were found in seven of 259 coprocultures evaluated. During the study, 125 horses were treated and 101 horses did not require treatment. Of these, six of the horses were sampled three times without exceeding the treatment threshold. The efficacy of both moxidectin and ivermectin was high (98.5% and 99.7% FECR), fenbendazole was expectedly low (57.7% FECR), and the efficacy of pyrantel was difficult to elucidate since all treatments were preceded by moxidectin. These results are consistent with other published studies that suggest using selective treatment to control equine GI parasites.