Christen said she recommends following standard modern recommendations for intestinal parasite control, which includes monitoring and treating horses on an individualized basis to limit the use of dewormers and, thus, reduce the risks of parasite resistance to treatment. | Photo: iStock

“We had anticipated that the deficient immune system of PPID horses would not be able to fend off intestinal parasites and that those horses would, therefore, excrete more eggs,” said researcher Garance Christen, DrMedVet, of the University of Bern Vetsuisse Faculty Swiss Institute of Equine Medicine and Agroscope Bern, both in Switzerland. “But our study showed that that’s not what’s happening.”

Christen and colleagues Nathalie Fouché, DrMedVet, Dipl. ECEIM, and Vinzenz Gerber, DrMedVet, PhD, Dipl. ACVIM, ECEIM, recently determined that horses with preclinical PPID (that is, they have blood values suggestive of PPID but aren’t yet showing clinical signs of disease) did not have higher fecal egg counts than healthy horses.

Christen, Fouché, Gerber, and colleagues followed a group of 48 senior horses (average age 24 years), none of which showed outward signs of PPID, living in a Swiss equine retirement facility in Switzerland. The horses had not been dewormed for four months before the study. They tested their subjects’ ACTH (adrenocorticotropic hormone) levels—which are elevated in horses with PPID—and diagnosed horses with PPID if they had concentrations of at least 35 pg/mL in July (ACTH level vary based on season, with the highest occurring in the autumn). The researchers treated half the PPID horses with pergolide for three months and the other half with a placebo for the same period