Equine helminth infections: control by selective chemotherapy

Area of Science:

• Veterinary Parasitology
• Equine Health Management
• Anthelmintic Resistance

Background:

• Internal parasite control in horses is crucial for herd health.
• Selective anthelmintic therapy aims to reduce drug resistance and treatment costs.
• Monitoring fecal egg counts (FEC) is a key component of parasite management.

Purpose of the Study:

• To evaluate the effectiveness of a selective anthelmintic therapy program in a horse herd.
• To determine if initial fecal egg counts predict future parasite shedding and treatment needs.
• To assess the long-term efficacy of selective deworming strategies.

Main Methods:

• A herd of 31 horses underwent selective anthelmintic therapy over a year.
• Fecal egg counts (FEC) were performed bimonthly.
• Horses with FEC ≥ 100 eggs per gram (epg) received ivermectin; others were untreated.
• Herd median FEC ≤ 100 epg was the criterion for adequate control.

Main Results:

• Selective therapy initially achieved adequate control (median herd FEC 0 epg after nine months).
• Parasite levels rebounded after horses returned to pasture (median herd FEC 325 epg).
• Initial September FEC significantly correlated with the following September's FEC and predicted treatment frequency.
• Horse age did not correlate with treatment requirements.

Conclusions:

• Selective anthelmintic therapy can be effective in the short term but requires ongoing monitoring.
• Initial fecal egg counts are valuable predictors for targeted deworming strategies in horses.
• Incorporating FEC into strategic anthelmintic programs can economically identify and manage high-shedding horses.