Efeito do clima e do fungo Duddingtonia flagrans sobre o desenvolvimento e migração vertical de larvas infectantes de helmintos parasitos gastrintestinais de ovinos em pastagem de capim Massai

Abstract

The use of nematophagous fungi is an interesting alternative for the biological control of trichostrongylids in ovine. However, for the effectiveness of the fungal isolate, it is able to pass through the gastrointestinal tract of the ruminant, develop in stool in the environment and prey satisfactorily infective larvae. Thus, this study aimed to determine the best time floating chlamydospores of Duddingtonia flagrans (CG768) for determining the number of chlamydospores per gram of feces (CPG) in sugar solution (experiment 1) and to evaluate the influence of this fungus and weather conditions to control infective larvae (L3) Trichostrongylidae of sheep grazing grass formed by Massai in three seasons in the northern region of the State of Mato Grosso (experiment 2). For the experiment 1, the chlamydospores grown on rice were supplied by oral dose of around 3,5x106 chlamydospores / kg body weight to two sheep. The stools were collected and five samples from each animal were processed using saturated solution of sugar (1,27 g/ml) for quantification of chlamydospores in McMaster chamber. The samples in the chambers were quantified in different floating time: 15 min, 30 min, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h and 48 h. The density of the sugar solution was also measured in the same diferente times under similar conditions. CPG counts increased along time to maximum of 25.5 hours and after that CPG counts decrease (R² = 0.8806, P <0.05). The following equation was generated to estimate the result of CPG in 25.5 hours of fluctuation from the results in 15 min: 𝐶𝑜𝑛𝑡𝑠 (25,5 ℎ𝑠) = {[(√𝐶15𝑚𝑖𝑛 + 1) × 2,793] 2 } − 1. For experiment 2, a paddock was formed with Massai grass and was used 60 experimental units in each station, and each one received a stool sample containing approximately 60,000 eggs of sheep nematodes with or without chlamydospores of D. flagrans. Fecal samples were collected from naturally infected sheep or dewormed, who received a dose of 3,5x106 chlamydospores / kg body weight orally. Fecal samples were deposited on pasture at half of each season and grass samples were colleted from > 15 cm, grass samples < 15 cm, remaining feces and soil in a 5 cm radius after 14 days. Samples were collected at three different times of the day being the average of larvae recovered along the day. The higher larval densities (L3 / kg of dry matter) were observed in autumn, followed by summer and winter. The remaining stool and the two layers of grass had similar average and the lowest recovered larvae average were observed in the soil. There was effect of the fungus Duddingtonia flagrans with a field predatory efficacy of 26.18%, 8.10% and 7.03% in the summer, autumn and winter respectively. There was a significant interaction between season and collection point (P <0.0001) on the average of recovered larvae. In winter, there was no difference between the collection points in the unfolding of the interaction. The autumn is the most favorable season to the development and migration of larvae in the grass environment offered by Massai. However the summer, the rainiest season, favors the persistence of larvae in the grass base and remaining stool. While the winter, which corresponds to extremely dry period, is the most unfavorable season for the development and migration of infective larvae of sheep parasites in grass Massai in the northern Mato Grosso state.