The possibilities and limitations of evasive grazing as a control measure for parasitic gastroenteritis in small ruminants in temperate climates.
Between 1999 and 2003 studies were done at Utrecht University on the population dynamics of gastrointestinal nematodes and the potential to use evasive grazing for the control of nematode infections in small ruminants. On most pastures grazed in May and June it took at least 3 weeks before high pasture infectivity levels for Haemonchus contortus developed while it took at least 2 weeks on pastures grazed in July, August and September. Occasionally, larvae emerged earlier on pasture when high temperatures coincided with rain. Pasture infectivity levels for H. contortus subsequently increased and the highest levels were found between 5 and 9 weeks on pastures grazed in May-June and between 3 and 9 weeks on pastures grazed in July, August and September. Pasture infectivity usually had decreased again to low levels after approximately 3 months. Larvae of the other trichostrongylids emerged later on pasture. However, patterns of Teladorsagia circumcincta, Trichostrongylus spp. and Cooperia curticei were basically similar to H. contortus. Strongyloides papillosus larvae emerge within 2 weeks on pasture and survival is short. On the other hand Nematodirus larvae took a lot longer to emerge on pasture than the other trichostrongylids. The results imply that only on a small proportion of farms (mixed dairy cattle/sheep farms; some organic dairy goat farms) evasive grazing can be recommended as only control measure for parasitic gastroenteritis. However, the present data offer possibilities to combine evasive grazing with other methods in an integrated control scheme.