Comparison of prevalence and strongyle egg counts per gram of feces in horses at pasture and in stables following ivermectin/praziquantel treatment

Abstract

Equine strongyle infections are prevalent among grazing horses worldwide, yet research on anthelmintic efficacy and parasite management strategies in South Korea remains limited. This study investigated the infection dynamics and parasite burden in horses managed under different systems (pasture vs. stable) over a one-year period in Jeju, South Korea, assessing the impact of management practices on parasite burden and the effectiveness of current deworming regimens. Thirty-two horses were administered ivermectin/praziquantel in June 2022 and assigned to either pasture (n = 16) or stable (n = 16) groups. Each group was further divided based on deworming intervals (3–6-3 months vs. 9–3 months). Monthly egg per gram (EPG) counts of strongyle eggs were conducted to evaluate seasonal variations in parasite burden. Results indicated that stabled horses maintained near-zero EPG levels year-round, whereas pasture-managed horses exhibited significant seasonal fluctuations, with EPG values peaking in summer and autumn before declining in spring. Deworming intervals had minimal impact on parasite burden in stabled horses. However, pasture horses showed varying reinfection risks, with the highest EPG value increase occurring in summer. These findings suggest that routine three-month deworming may be excessive for stabled horses but adequate for pasture-managed horses due to higher reinfection rates. Instead, targeted selective treatment based on EPG monitoring is recommended as a more effective and sustainable parasite control strategy to optimize deworming regimens and mitigate anthelmintic resistance.