The efficacy and persistent anthelmintic effect of ivermectin in sheep

Area of Science:

• Veterinary Parasitology
• Pharmacology
• Sheep Health

Background:

• Gastrointestinal nematodes pose a significant threat to sheep health and productivity.
• Ivermectin is a widely used broad-spectrum anthelmintic in livestock.
• Evaluating the long-term efficacy of different ivermectin formulations is crucial for effective parasite control programs.

Purpose of the Study:

• To compare the direct efficacy and long-term persistent anthelmintic effects of oral and injectable ivermectin formulations in sheep.
• To assess the duration of ivermectin's protective effect against key gastrointestinal nematode species.

Main Methods:

• Sheep lambs were experimentally infected with Haemonchus contortus, Trichostrongylus vitrinus, and Cooperia curticei.
• Animals were treated with either an oral suspension or injectable ivermectin at 0.2 mg/kg.
• Reinfection with larvae occurred 3, 6, or 10 days post-treatment, followed by post-mortem worm counts.

Main Results:

• The oral ivermectin suspension exhibited no persistent anthelmintic effect.
• The injectable ivermectin formulation demonstrated sustained efficacy for up to 10 days against H. contortus.
• Injectable ivermectin achieved 100% reduction in C. curticei and T. vitrinus burdens when reinfection occurred 6 or 10 days post-treatment.

Conclusions:

• Injectable ivermectin offers a significant persistent anthelmintic effect in sheep, crucial for managing nematode reinfections.
• Oral ivermectin suspension lacks the sustained efficacy needed for long-term parasite control in sheep.
• The injectable formulation provides extended protection, particularly valuable in high-risk parasite exposure scenarios.