Activity of closantel in the prevention of Gasterophilus and Strongylus vulgaris larval infections in equine foals and yearlings.

This research study investigates the optimal dosage and duration of activity of an oral drug called “closantel” in preventing Gasterophilus and Strongylus vulgaris larval infections in horse foals and yearlings.

Design of the Experiment

• The study was designed in two experiments involving foals and yearlings (horses 1 to 2 years old).
• They tested different dosages of an oral medication called closantel, with specified amounts given according to the body weight of the animal.
• The horses were allowed to graze on open pasture to naturally source bot and helminth (worm) infections. After a period, the horses were euthanized and studied to see if the medication effectively prevented the infections.
• Some horses were kept as controls, meaning they received no medication to provide a comparison of infection levels.

Results of Experiment 1

• In the first experiment, various doses of closantel were tested (0 mg/kg, 2 mg/kg, 5 mg/kg, or 8 mg/kg). These doses were administered every 2 months during the bot season.
• Different outcomes were observed in foals and yearlings. For young foals, all the doses were highly effective (98.6% to 100% effective) in preventing Gasterophilus spp larval infections.
• However, for yearlings, only the highest dose (8 mg/kg) showed significant activity (99.7% effective).
• This dosage also notably reduced the numbers of 4th-stage and immature adult Strongylus vulgaris in the mesenteric arteries (a branch of arteries important for digestion) as compared to untreated controls, showing the effectiveness of the drug against two different types of infections.

Results of Experiment 2

• In the second experiment, all animals were given a single treatment of the highest dose of closantel (8 mg/kg), and studied at 1, 2, and 3 months after treatment.
• It was found that closantel remained effective for up to 2 months in preventing G. intestinalis larvae infections in both foals and yearlings.
• No signs of harmful health effects or toxicosis were observed in the animals receiving treatment in either experiment.

Overall Findings

• The study concludes that closantel is an effective drug for preventing Gasterophilus and S. vulgaris larval infections in equine foals and yearlings, with an optimal dosage of 8mg/kg of bodyweight.
• The effectiveness of the drug lasts for about 2 months after a single dose is administered, providing a timeframe for its protective effect.
• The study provides important facts for equine health management, especially for comprehensive parasite control practices in younger horses.