EN
The purpose of the study was to evaluate the influence of the pasture season on the level of strongyles infection in horses from a multi-herd farm. The investigations comprised Pure Blood Arabian horses: yearlings (n = 70-101), two-year-olds (n = 62-80) and mares (n = 141-148) kept in the pasture-housed system and dewormed twice a year, before and after the pasture seasons, with ivermectine. Fecal egg counts (Mc Master method) and larvae culture by Henriksen and Korsholme were conducted each year in April, June, August and in October in the years 2004-2006. Based on the obtained results, the mean prevalence of the infection (%), EPG and the percentage of cyathostomes or strongyles in Strongyliae community were calculated. The mean seasonal prevalence of the infection with small strongyles as well as EPG were the highest in 2004 and were consistently dropping in all groups of horses in the following years. Two-year-old horses were infected the most: on average they have been expelling 1630 EPG in 2004 while only 165 EPG in 2006. A high strongyle egg count in horses in the autumn has an influence on a high level of the infection in the spring of the following year. Consequently, a low level of strongyles infection in the autumn causes a low egg output in the spring of the following year. Larval differentiation revealed a dominance of small strongyles (Cyathostominae), whereas the population of large strongyles (Strongylinae) was lower than 1%. The dropping level of strongyle infections in horses observed in the studies in the subsequent years might have been caused by climatic factors (high temperature and low humidity), which did not favor the development and survival of infective strongyles larvae on pastures.