Efficacy of Daily Pyrantel Tartrate (Strongid C) against Strongyles in Ponies on Pasture

A clinical trial was conducted with 2- to 3-year-old ponies to determine the effectiveness against strongyles of 2.64 mg pyrantel tartrate/kg body weight administered in the daily ration throughout a pasture season in Canada. Ten ponies were given the anthelmintic, and 10 were not treated and served as controls. Each group of ponies was on a separate pasture. The mean strongyle eggs/g of feces for each group, before treatment and turnout to pasture, was greater than 2,200. Thereafter, the mean eggs/g feces for the untreated group remained high (1,405−2,294) and those for the treated group decreased markedly to, and remained at, very low levels (0.2−16.8). Strongyle larval counts for the pasture with the untreated ponies rose to 26,790 larvae/kg dry herbage in August, whereas that for the treated group was 610 larvae/kg dry herbage. At the end of the season, two ponies from each group were isolated for 6 weeks and necropsied. The mean number of strongyles in the untreated and treated ponies was 69,288 and 8,452.5, respectively. In the untreated ponies, 21 species of strongyles were found, and approximately 84% of them were from eight species of cyathostomes. In the treated ponies, 14 species of strongyles were found, and approximately 77% were from one species, Cylicostephanus minutus (52.0%), and immature cythostomes (25%). Adverse reactions were not observed in any of the treated ponies. Pyrantel tartrate was highly effective in significantly reducing the strongyle egg and pasture larval counts and the transmission of strongyles during a pasture season.