EFEITO DE TRêS ESPéCIES DE GRAMíNEAS FORRAGEIRAS SOBRE A ESTRUTURA DA PASTAGEM E DISTRIBUI O VERTICAL DE LARVAS INFECTANTES DE NEMATóDEOS GASTRINTESTINAIS DE OVINOS

The knowledge of interaction between infective larvae setting and the type of grass is important to epidemiological studies and the control of gastrointestinal nematodes in sheep. The objective of this work was to evaluate the effects of three species of forage grasses on pasture characteristics and the vertical distribution of infective larvae (L3) of gastrointestinal nematodes of woolless sheep on the grasses during the rainy season. Sixty non-periparturients ewes were used, naturally infected, equally distributed on 2 ha paddocks sowed with Tanzania, star, and gamba grasses, managed under continuous grazing system, from October 2003 to March 2004, at Santa Bárbara farm, Barreiras–Bahia-Brazil. Data of three samples between December 2003 and March 2004 were analyzed by SAS, using split-plot design, with 10 replications. Infective larvae of Haemonchus spp. and Trichostrongylus spp. were observed on forage in all stratus of vertical layer of the grasses without a defined pattern. Pastures with different characteristics under continuous grazing system had good conditions for developing infective larvae of sheep.