Evaluation of parasiticidal activity of fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate in horse foals with emphasis on ascarids (Parascaris equorum) in field studies on five farms in Central Kentucky in 2007.

This research conducted field studies in 2007 on five horse farms in Central Kentucky to evaluate the effectiveness of four drugs on treating internal parasites, in particular, ascarids, in horse foals.

Study Design and Procedure

• The researchers used paste formulations of four compounds for the study: fenbendazole (FBZ), ivermectin (IVM), oxibendazole (OBZ), and pyrantel pamoate (PRT). The main focus was on combating ascarids (Parascaris equorum), a kind of roundworm, as there is widespread resistance to the commonly used IVM.
• Apart from ascarids, the study also aimed to gather data on small strongyles, another type of internal parasite in horses. To identify the presence of these parasites, researchers analyzed horse fecal samples using a qualitative (presence or absence) or quantitative method (eggs per gram of feces).
• To ensure the correct dosage, a girth tape was used to estimate each foal’s body weight. Some foals underwent more than one treatment cycle.
• The efficacy of the tested drugs was assessed by calculating the average reduction in the number of foals passing eggs after treatment compared to before treatment.

Results

• FBZ was tested on four farms on 76 foals. It reduced ascarid eggs in 50 foals by 84% but showed 0% reduction in strongyle eggs in 62 foals.
• IVM was tested on three farms on 58 foals. It demonstrated no reduction (0%) in ascarid eggs in 18 foals but fully eliminated (100% reduction) strongyle eggs in 48 foals.
• OBZ was tested on three farms on 181 foals. It led to a reduction of 94% for ascarid eggs (in 78 foals) but showed no effect (0% reduction) against strongyle eggs (in 79 foals).
• PRT was tested on two farms across 60 foals at two different doses. At the smaller dose, it showed a 0% reduction in ascarid eggs and a 12% reduction in strongyle eggs. At the larger dose, reductions were 23% for ascarid eggs and 27% for strongyle eggs.

Conclusion

• The results indicated substantial differences in the impact of different drugs on ascarid and strongyle infestations in horse foals. Both FBZ and OBZ demonstrated significant reductions in ascarid egg counts while IVM and PRT showed less effectiveness.
• It’s important to note that none of these drugs, except for IVM, had a noticeable effect on strongyle infestations. IVM was completely effective against strongyles, showing a 100% reduction in strongyle egg count.