The efficacy of a combination anthelmintic against oxibendazole resistant small strongyles, large strongyles and ascarids in horses.

The researchers explored the effectiveness of a blend of anthelmintic agents against certain resistant parasites in horses, including resistant small and large strongyles, and ascarids. They found that a combination of anthelmintics with different mechanisms of action could effectively combat these parasites.

Background and objectives

• The study was designed due to the wide-spread resistance developed against certain anthelmintic drugs by small strongyles, large strongyles, and ascarids in horses.
• Oxibendazole, which was previously an exception to this resistance, has started showing signs of reduced effectiveness, signaling the emergence of resistance in the United States and Australia.
• The objective of the study was to test the efficacy of a combination of anthelmintics (morantel tartrate, dichlorvos, oxibendazole, and fenbendazole), used alone or in combination, on a group of 60 horses aged over 8 months old.

Methods

• The researchers selected 60 horses from a group of 120 on a farm in the Goulburn area of NSW, Australia where benzimidazole resistance was suspected due to heavy stocking rates and frequent treatments with oxfendazole.
• The horses were divided into six groups of 10 based on a random rank order of strongyle egg count to ensure a similar range and group mean egg count across all groups.
• Two additional groups were chosen based on the presence of Parascaris equorum eggs in their feces.
• Each group was given different treatments: one of the four anthelmintics or a combination of dichlorvos, oxibendazole and morantel tartrate. The anthelmintics were formulated in a water-based gel for palatability and stability.
• One group of horses remained untreated to serve as a control group.

Testing and analysis

• Fecal samples were taken at 14, 27, and 49 days after treatment (DAT) from each horse. The samples were pooled by group to form a fecal culture, incubated, and larvae were then examined.
• The larvae were differentiated based on their size, shape, and the number of intestinal cells.

This research highlighted that a careful combination of anthelmintics might prove a potential solution to commonly resistant internal parasites in horses. Further research is needed to validate these findings over a prolonged period.