L. Gruner et S. Suryahadi, IRRIGATION, FECAL WATER-CONTENT AND DEVELOPMENT RATE OF FREE-LIVING STAGES OF SHEEP TRICHOSTRONGYLES, Veterinary research, 24(4), 1993, pp. 327-334
The effect of irrigation by flooding the pastures on the ability of th
e eggs of sheep Trichostrongyles to develop into infective larvae (L3)
was estimated in outdoor conditions by depositing parasitised faeces
on plots, without irrigation or submerged, at different times and dura
tions. The rates of development of Teladorsagia circumcincta, Trichost
rongylus vitrinus and Chabertia ovina were very low in spring and summ
er in dry plots but proportional to the duration of submersion in the
irrigated plots. T circumcincta was mainly favoured in spring, T vitri
nus in summer, but higher rates were observed in autumn. The action of
water had more effect on freshly deposited faeces. In laboratory expe
riments on T circumcincta, T vitrinus and Haemonchus contortus, the su
bmersion of cultures was unfavourable to egg development but favoured
L1 development. Cultures with different faecal water contents (FWC) si
mulating a submersion (7 or 16 h) or an alternance of spraying and deh
ydration, or at constant values of 60 and 50% enabled us to conclude t
hat high FWC favoured the development of T vitrinus, had some negative
effect on T circumcincta, but H contortus was more susceptible to var
iations of FWC. The FWC had an effect on the size of L3 and, for T cir
cumcincta only, the survival rate of the small L3 obtained at low FWC
seemed decreased. These data could explain the absence of H contortus,
as well as the abundance of T vitrinus on the studied pastures.