Periódicos Brasileiros em Medicina Veterinária e Zootecnia

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Variability in the infection of F1 Katahdin x Pelibuey crossbred lambs to gastrointestinal parasitic nematodes in a warm humid climate

González Garduño, RobertoPedro Pedro Pedro PedroTorres Hernández, Glafiro

Background: In sheep production systems based on grazing, gastrointestinal nematodes (GIN) are one of the main problems faced by farmers. The occurrence of anthelmintic resistance in GIN has endangered the productive activity of sheep, so that one alternative has been through the selection of sheep. The selection programs are based on evaluation of parasitism by measuring the fecal egg counts (FEC) of GIN due to the high correlation between the FEC and worm burdens. The identification of resistant and susceptible lambs requires knowing the FEC after the infection. The aim of this research was to determine the intra-breed variability on FEC of GIN in Katahdin x Pelibuey grazing sheep.Materials, Methods & Results: The experiment was conducted in Tabasco, Mexico in a warm humid climate. The study was carried out in three stages: in stage I, the FEC was recorded in newly weaned lambs experimental infected with 1600 infective larvae (L3 ) of Haemonchus contortus and Cooperia curticei (85% and 15% respectively). Twenty lambs were drenched with albendazole and 20 more lambs were considered as control without any anthelmintic treatment. In stage II acquired resistance was determined in the same animal group after a break period following the same treatments. In stage III new lambs were introduced to paddocks and the FEC was recorded in their first infection. Every 15 days fecal sam

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