Larvae population of helminths infesting lambs grown on native pasture in Roraima, Brazil

Abstract

A study of the populational dynamics of infective larvae of gastrointestinal helminths of lambs was conducted from October, 1986 to September 1988 in native pasture in Roraima, Brazil. Every 30 to 35 days, two lambs remained on the pasture with approximately 300 animals, totalling 44 helminth-free tracer lambs. The nematode Haemonchus contortus was found in all the animals. The greater number of these infective larvae was found in the pasture during months of higher precipitation, while at the end of the lower precipitation period it decreased. Trichostrongylus colubriformis, Cooperia curticei, Oesophagostomum columbianum, Trichuris sp. and Moniezia sp. were also found among the tracer animals. As temperature and relative humidity remained high and unchanged during the whole period, precipitation was the most important climatic factor for development and survival of larvae. Hence, the period with higher water deficits, (the most unfavorable), is important in the adoption of control strategies.