[Recovery of Trichostrongylus colubriformis infective larvae from three grass species contaminated in summer].

The purpose of the experiment was to evaluate infective Trichostrongylus colubriformis larvae (L3) survival in three forage species. Experimental plots, planted with Brachiaria decumbens cv. Australian, Cynodon dactilon cv. Coast-cross, and Panicum maximum cv. Aruana, were used in the study, totaling two plots for each species. Each plot (32.4 m(2)) was divided into 36 subplots (30 x 30 cm) in order to allow six replicates per forage species and per herbage height in each week of material collection. Larval recovery was evaluated from middle summer to middle autumn under the effect of two forage paring heights: low, 5 cm, and high, 30 cm. The paring was carried out immediately before the fecal samples with T. colubriformis eggs, taken from sheep, were deposited on pasture in 05/Feb/2004. Feces and forage collection was performed one, two, four, eight, 12 and 16 weeks after feces deposition in the experimental plots. Forage grass height was measured in each subdivision immediately before the collections. The forage sample was cut, close to the soil, from an area delimited with a circle with a 10 cm radius. The feces were collected from the subplots. The number of infective larvae recovered from pasture was very small in comparison with the amount of larvae produced in cultures maintained in laboratory (maximum 6.7% on Aruana grass with 30 cm). L3 recovery rates from fecal samples were bigger when the feces were deposited on high grass (measuring 30 cm - P<0.05). L3 recovery from pasture and L3 concentration on herbage (L3/Kg dry matter) were similar for both cuts (P>0.05). Among the forage species, the Aruana grass was the one that, in general, harbored the biggest concentrations of infective T. colubriformis larvae.