Ecological studies on the development of the pasture stages of Nematodirus battus and N. filicollis, Nematode parasites of sheep

Abstract

1. The availability of Nematodirus infection to sheep was followed by grazing successive pairs of worm-free lambs on a contaminated plot. It was shown that lambs did not become infected during the summer following pasture contamination in the spring, but became infected when they were grazed on the plot the following spring.2. The development and hatching of the eggs and larval stages of N. battus and N. filicollis were followed by the periodical examination of infected faeces set out during May-November. The results showed that development to the infective larval stage occurred during the summer, taking normally about 3 months, but that the larvae then remained dormant within the egg membranes until the following spring.3. Laboratory studies confirmed the hypothesis that the hatching of the infective larvae was a response to a rise in temperature in the spring, following sensitization by exposure to low temperature during the winter. A rise in temperature to 50° F. was necessary before a high percentage hatch occurred.4. The epidemiology of Nematodirus infection is discussed in relation to these observations.

Seasonal incidence of infective trichostrongyle larvae on pasture grazed by lambs

“…The seasonal incidence of Nematodirus spp. larvae on pasture is well documented (Baxter 1958;Gibson 1958Gibson ,1959Gibson ,1963Gibson ,1965Spedding et al, 1958;Thomas 1959;Thomas & Stevens 1960). Larvae of the two species commonly found at Wallaceville (N. filicollis and N. spathiger) occur in the same broad two-peak pattern as other larvae, the results of the present study confirming the earlier findings of Brunsdon (1960Brunsdon ( , 1963a.…”

“…In Britain two patterns of larval occurrence were found for N. filicollis, one for the north of England (Thomas & Stevens 1960) and the second for the south (Gibson 1963), the pattern at Wallaceville being broadly similar to the latter. Eggs deposited on pasture in spring hatch in late summer-autumn, the resultant larvae overwintering in large numbers until the following spring.…”

The contribution to the epidemiology of gastrointestinal nematodes of sheep with special focus on the survival of infective larvae in winter conditions

“…It is interesting that this parasite adapts well to colder climates (Thomas and Stevens 1960;Gibbs 1979;Gibson and Everett 1981;Gibbs 1986) and has the likelihood of arctic origin (van Dijk and Morgan 2008). Embryonated eggs did not hatch in temperatures below 11°C or above 17°C, and some proportion eggs hatched only after being chilled and 50% of infective larvae survived for 220 days at −5°C (Ash and Atkinson 1986;van Dijk and Morgan 2008).…”

A survey of the prevalence ofNematodirus spathigerandN.filicollison farms in the North and South Islands of New Zealand

“…Compared with N. spathiger, N. filicollis is generally much slower in completing the pre-parasitic phase of its lifecycle due to its requirement for chilling (Thomas and Stevens 1960;Van Dijk and Morgan 2009). By measuring the numbers of larvae on pasture, the results of Vlassoff (1982) may have been influenced by a greater opportunity for chilling of developed eggs of N. filicollis in the south, due to the generally lower temperatures, than in the north.…”

“…By measuring the numbers of larvae on pasture, the results of Vlassoff (1982) may have been influenced by a greater opportunity for chilling of developed eggs of N. filicollis in the south, due to the generally lower temperatures, than in the north. Similarly, because N. filicollis will generally not hatch in a faecal culture without subsequent chilling (Thomas 1959;Thomas and Stevens 1960), it is unlikely to be encountered in routine laboratory diagnostics, potentially reinforcing the perception that it is less prevalent in some parts of the country. This was the case in the current study and resulted in the addition of a chilling period for half of each sample, so that fair comparisons between species could be made.…”