Effects of irrigation on appearance and survival of infective larvae of goat gastro-intestinal nematodes in Guadeloupe (French West Indies).

In Guadeloupe (French West Indies), faeces from naturally infected goats were deposited during the dry season on three plots, irrigated with long (plot A) or short herbage (B) and non-irrigated with long herbage (C). Microclimatic data and the evolution of L3 population size in faeces, on soil surface and on herbage were followed over a period of 26 days. The initial nematode egg population was comprised of 58% Haemonchus contortus (HC), 25% Trichostrongylus colubriformis (TC) and 17% Oesophagostomum columbianum (OC). Temperature and water content varied in time and space (soil, faeces, herbage) from homogeneous in A to very heterogeneous in C. In A and B, population dynamics were similar with higher values of maxima in A. Larval peaks occurred on day 9 after deposition in faeces in plot A: 23.1, 39.1 and 17.2 L3/100 eggs, respectively for HC, TC and OC; the same day in soil: 1.9, 0.6 and 3.1 L3/100 eggs. On day 26 it remained less than 1 L3/100 eggs in both soil and herbage for the three species. In C, only TC larvae were observed coming, after rain, from eggs in which hatching had been delayed. It was difficult to separate the respective effects of temperature and water content on the development of the eggs, but irrigation gave favourable conditions for all eggs to develop into larvae. Pasture rotation with 28-35 days of regrowth should minimize the increased risk of infection for the goats due to irrigation.