A field evaluation of anthelmintics in horses in Sweden.

The researchers conducted a study on 336 horses in Sweden in 1986 to analyze the efficacy of anthelmintics or deworming drugs. Findings demonstrated a significant variation in drug effectiveness against small strongyles, a common parasitic worm in horses.

Background of the Study

• The study field evaluation of anthelmintics was carried out on 336 horses scattered around 37 farms in Sweden from February till May in 1986.
• The horses which were a part of the study were all grazers on permanent pastures and were administered treatments for parasites a minimum of three times in a year.

Purpose of the Study

• The main goal of the study was to evaluate the efficacy of the anthelmintic or deworming drugs in horses.
• In specific, they aimed to see how effectively these drugs treated small strongyles, a type of intestinal parasite common in horses.

Findings of the Study

• The study revealed that small strongyles were resistant to (pro)-benzimidazole drugs (a type of anthelmintic) in almost all but one of the 23 herds examined.
• Around 7 days after the treatment, approximately 30% of the 205 horses that were examined were found to be shedding less than 100 eggs per gram, indicating that the parasites were still present, albeit in lower quantities than before treatment.
• The study found substantial variation between herds in terms of faecal egg-count depression (range: 6.4%-90.4%) and drug efficacy (range: 0.0%-80.0%). This points towards the influence of various factors including the general health of the horse, the environment and the specific strain of parasite involved.
• In contrast to the (pro)-benzimidazole drugs, other drugs that were not benzimidazole managed to fully treat mature small strongyles, suggesting the need to use different drugs for treating different types of parasites or different stages of parasite maturity.