During each of 25-56 days periods from January 08, 1988 to May 05, 1990, two male sheep three to six month old, shown to be free of gastrointestinal nematode infection, were grazed with a flock of naturally infected sheep (tracer sheep). At the end of each grazing period, these sheep were placed on a cement floored pen and were maintained there for two to three weeks prior to necropsy and examination for gastrointestinal nematodes. Haemonchus contortus was the most prevalent nematode found (80%). The mean number of this nematode varied from 510, acquired during the dry season, to 2157, acquired during the rainy season. The mean number of inhibited larvae of H. contortus was 499 in the rainy season (23 % of the total acquired in the season) and 416 in the dry season (81,6% of the total acquired in the season). Trichostrongylus spp. (T. axei and T. colubriformis), Cooperia spp. (C. pectinata and C. punctata), Oesophagostomum radiatum and Strongyloides papillosus occurred in 72%, 72%, 56% and 38% of the examined animais, respectively. The acquisition of nematodes by tracer sheep occurred mainly from mid-rainy to early dry season.
Sheep; gastrointestinal nematode infection; epidemiology; control
