Parasite field study in central Kentucky on thoroughbred foals (born in 2004) treated with pyrantel tartrate daily and other parasiticides periodically.

The research conducted a field study of parasite treatments on thoroughbred foals in central Kentucky. The study was intended to evaluate the effectiveness of daily pyrantel tartrate and periodic alternative parasiticides in managing internal parasites in the foals over a 14-month period.

Study Methodology

• The study features 79 thoroughbred foals, born in 2004, on three different horse farms in central Kentucky identified as C, M, and S.
• The foals started receiving daily doses of pyrantel tartrate at about 3 months of age. They also got periodic doses of other parasiticides which included fenbendazole, ivermectin with or without praziquantel, oxibendazole, pyrantel pamoate, and moxidectin.
• The farm staff were responsible for administering all treatments.
• From May 2004 through July 2005, the research team collected 989 feces samples from the foals for analysis. The objective was to identify internal parasite eggs/oocysts through qualitative and/or quantitative methods.
• The conclusions on drug activity had to factor in the combined effect of pyrantel tartrate and the other parasiticides.

Study Findings

• With reference to small strongyles, the activity of the drug used had to do with the specific additional compound in use.
• The researchers evaluated drug activity based on the percentage of foals with strongyle-egg-positive feces and/or level of eggs per gram (EPG) of feces after treatment. Moxidectin showed highest activity, followed by ivermectin, fenbendazole, oxibendazole, pyrantel pamoate, and fenbendazole (administered twice for five days).
• The macrocyclic lactones (moxidectin and ivermectin) were highly effective compared to other drugs.
• Some foals on one particular farm (S) exhibited high strongyle counts, especially during periods of receiving only pyrantel tartrate. However, these counts dropped significantly or even went negative a few days after receiving ivermectin or moxidectin.

Other Findings

• Three foals had ascarid eggs in their feces post-treatment with a combination of ivermectin and praziquantel.
• The qualitative method was more effective than the quantitative technique in detecting strongyle and ascarid eggs.
• For ascarid eggs (from Parascaris equorum), the researchers observed low prevalence (0, 4 and 31%). The prevalence rates for strongyles, however, were high (80, 100 and 100%). Only one foal was found infected with Strongyloides westeri, while the prevalence of Eimeria leuckarti was observed as medium to high (36, 41 and 85%) across the three farms C, M, and S, respectively.
• The researchers were unclear if the low prevalence of ascarid was due to the effectiveness of pyrantel tartrate and other drugs or resultant of a limited source of infective eggs.