Publisher
BMC
Abstract
Background: Nematodirus battus, unlike most other gastrointestinal nematodes, undergoes maturation to an infec-
tive larva within the egg. Historically, eggs were considered to require a period of chilling over winter followed by
a period of temperature above 10 °C for synchronous hatching to occur (generally in spring). Anecdotal reports of
Nematodirus infection out-with spring in veterinary journals and the farming press suggest that the concentrated
pasture abundance of N. battus infective larvae may be changing. In order for control practices to be adapted, and
unexpected disease outbreaks to be avoided, it is important to quantify how parasite epidemiology is changing and
research the drivers behind it.
Method: The present study investigated the in vitro hatching response to temperature experiences (with and with-
out a period of chilling) for egg samples of 90 N. battus populations obtained from 73 commercial sheep farms. Six
aliquots of larvated eggs were prepared per population, three aliquots were placed at 4 °C for 6 weeks to provide a
chill stimulus then incubated at the optimal hatching temperature for the species. The remaining three aliquots of
eggs were incubated at the hatching temperature without a prior chill stimulus and the number of hatched larvae
was compared between treatments.
Results: Median hatch rate across all populations with chilling was 45% (95% CI: 42-48%) and without chilling was
4% (95% CI: 2-6%). Inter-population variation in hatching ranged from 0 to 87% of eggs able to hatch in the absence
of a chill stimulus, mean non-chill hatching was 13 ± 2% of eggs (mean ± SE). Non-chill hatching rates were greater
than chilled hatching rates in seven of the 90 populations tested.
Conclusions: Clearly, the variation in hatching responses to temperature experience is very large and therefore the
seasonality of the parasite may vary not only between regions but also at farm level. In contrast to what previous work
has suggested, there was a geographical trend towards higher non-chill hatching in the Northern parts of the UK.
Year
2020
Category
Refereed journal