Migratory dynamics of cyathostomin larvae in a Bermuda grass pasture in South America

Studies of the migratory dynamics of cyathostomin infective larvae (L3) in different seasons and with two types of irrigation were carried out over 12 months (September 2006 to September 2007) in the subtropical climate of the Baixada Fluminense region of Rio de Janeiro state, Brazil. Four faecal masses weighing 500 g each from naturally infected horses were placed in a Bermuda grass (Cynodon dactylon) pasture in the beginning of each season. Samples of faeces and grass were collected every 15 days until the end of each season. The highest recovery in faeces occured in autumn (491,910 L3/kg dried herbage) and in pasture, it was achieved in winter (9,963 L3/kg dried herbage). The lowest number of infective larvae recovered from faeces (55,100 L3/kg dried herbage) and pastures (2,188 L3/kg dried herbage) were achieved in spring. The nonparametric Kruskal-Wallis test showed a significant difference in infective larvae recovery between the seasons. The collection time of the samples did not affect the larva recovery. The results suggest that in the conditions of the region studied, animals maintained in pasture are at permanent risk of infection.