The distribution of the infective larvae of sheep gastro-intestinal nematodes in soil and on herbage and the vertical migration of Trichostrongylus vitrinus larvae through the soil

Observations on the epidemiology of autumn nematodirosis in weaned lambs in a Scottish sheep flock

“…Few if any N battus larvae that hatched during the spring 2009 or 2010 would have been expected to have survived until autumn on the main part of the field, because they would have been removed with the silage crops during the summer, or succumbed to the effects of desiccation, ultraviolet light (Van Dijk and others 2009) or heavy rainfall. The identification of relatively small numbers of N battus infective larvae on the main part of the field during autumn 2009 and 2010 may have been the result of a relatively small secondary autumn hatch, in a manner that has previously been described in several countries (Borgsteede 1983, McKellar and others 1983, Hollands 1984, Rose and Small 1985, Rickard and others 1987). However, if it is assumed that the level of egg shedding onto the main part of the field and the strip of rough grazing was similar, then it is likely that the majority of the abundant N battus infective larvae that were identified on the rough grazing had hatched during the spring.…”

The influence of water on the migration of infective trichostrongyloid larvae onto grass

“…It was found that, after heavy rains followed by artificial watering of herbage, approximately 85% of larvae were still recovered in the top 5 cm of the soil while only 0·8% reached a depth of 25–30 cm. Rose and Small (1985) confirmed the ineffectiveness of rainfall in washing T. vitrinus larvae into the soil. Therefore, losses of larvae as the result of heavy rainfall appear to be very limited, at least in temperate regions.…”

“…Water present within faeces is likely to permit development to the infective third larval stage (L3) in most species in all but the most arid conditions (Chiejina and Fakae, 1989;Onyali et al 1990;Garcia Romero et al 1997). Although the continuous film hypothesis has become the established view amongst veterinary parasitologists it remains largely untested as most studies of L3 migration have been conducted in the field, with insufficient separation of different phases of migration, or control of environmental conditions (Skinner and Todd, 1980;Rose and Small, 1985;Krecek et al 1992;Marley et al 2006). This would have important implications for parasite transmission.…”

“…Thus, larval migration would only be possible either just after rains or when dew is found on grass leaves. Although the continuous film hypothesis has become the established view amongst veterinary parasitologists it remains largely untested as most studies of L3 migration have been conducted in the field, with insufficient separation of different phases of migration, or control of environmental conditions (Skinner and Todd, 1980; Rose and Small, 1985; Krecek et al 1992; Marley et al 2006). Silangwa and Todd (1964) compared migration onto wetted and non-wetted grass in the laboratory and concluded that trichostrongylid larvae climbed wetted grass significantly better.…”

Microclimate has a greater influence than macroclimate on the availability of infective Haemonchus contortus larvae on herbage in a warmed temperate environment

“…Although larval recovery from soil was unsuccessful in the experiments reported on here, possibly due to the dense turf structure and shallow soil/root layer with little free soil present, sequestration in soil could be an important modifier of larval availability under natural field conditions. Previous results vary widely, sometimes finding many larvae in soil (Callinan & Westcott, 1986;Krecek, et al, 1995;Leathwick, et al, 2011) and sometimes not (Crofton, 1948;Rose & Small, 1985).…”