Ivermectin performance in horses diagnosed with equine endocrine disorders

• Published in: Veterinary parasitology 2024-06, Vol.328, p.110182-110182, Article 110182
• Main Authors: Nielsen, M.K., Finnerty, C.A., Ripley, N.E., Page, A.E., McClendon, M.E., Adams, A.A.
• Format: Article
• Language: English
• Subjects: Animals; Anthelmintic; anthelmintics; Anthelmintics - pharmacology; Anthelmintics - therapeutic use; Antiparasitic Agents - pharmacology; Antiparasitic Agents - therapeutic use; Cyathostomin; Cyathostominae; deworming; Efficacy; Egg reappearance period; eggs; Endocrine System Diseases - drug therapy; Endocrine System Diseases - veterinary; fecal egg count; Feces - parasitology; Female; Horse Diseases - drug therapy; Horse Diseases - parasitology; Horses; insulin; ivermectin; Ivermectin - pharmacology; Ivermectin - therapeutic use; Male; Parasite Egg Count - veterinary; statistical analysis; Treatment; veterinary parasitology
• ISSN: 0304-4017; 1873-2550
• DOI: 10.1016/j.vetpar.2024.110182

Anthelmintic performance against equine cyathostomins can be evaluated by two different non-terminal measures; the Fecal Egg Count Reduction Test (FECRT) and the Egg Reappearance Period (ERP). Most available FECRT and ERP data have been determined in populations of young horses, and very little information is available from mature and senior horses. Furthermore, it is unknown how commonly occurring equine endocrine disorders such as Insulin dysregulation (ID) and Pituitary pars intermedia dysfunction (PPID) may interfere with these measurements, but it has been suggested that horses with these conditions could be more susceptible to parasitic infections. A research population of senior horses and horses with or without PPID, ID, or both were enrolled in this study. All strongylid egg count positive horses were included in an ivermectin (200 μg/kg) efficacy study. These were distributed among the following groups: ID: six, PPID: three, PPID and ID: seven, and healthy controls: three. Strongylid fecal egg counts were determined on the day of ivermectin administration, at two weeks post deworming, and on weekly intervals until eight weeks post treatment. Determination of FECRT and ERP were carried out following World Association for the Advancement of Veterinary Parasitology guidelines. Results revealed high ivermectin efficacy with mean egg count reduction at 99.7% or above in all groups at two weeks post treatment. Egg reappearance was documented at six and seven weeks in the ID and PPID/ID groups, respectively, whereas the PPID and healthy control groups both had ERP at 8 weeks. Statistical analysis found no significant differences in egg count levels between groups during the study. The expected ERP for ivermectin is 8–10 weeks, meaning that two of the groups displayed shortened ERPs. However, due to the small group sizes, these data should be interpreted with caution. Nonetheless, results do indicate a need for further investigation of the possible influence of endocrine disorders on anthelmintic performance in horses. •Ivermectin efficacy was >99.7% in all groups.•Shortened egg reappearance periods found in two Insulin Dysregulation groups.•No evidence of shortened egg reappearance period in the Pituitary Pars Intermedia Dysfunction group.