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Parasitic Gastroenteritis (view source)
Revision as of 15:19, 23 December 2008
, 15:19, 23 December 2008→Rate of Infection
*host appetite (under normal circumstances this is fairly constant, increasing with host liveweight); and
*host appetite (under normal circumstances this is fairly constant, increasing with host liveweight); and
*numbers of infective larvae (L3) on pasture (there are marked fluctuations in the number of L3 on pasture grazed by livestock during the year which help to explain the seasonal occurence of PGE).
*numbers of infective larvae (L3) on pasture (there are marked fluctuations in the number of L3 on pasture grazed by livestock during the year which help to explain the seasonal occurence of PGE).
Development from L1 → L2 → L3 is temperature dependent. Also, the L3 cannot feed as it is ensheathed (i.e. enclosed in the shed L2 cuticle). Its life-span therefore depends on how quickly its food stores are used up, and this too is temperature dependent as it is more active in warm weather.
a) ''Infective larvae (L3) overwinter on pasture'':
*if infected stock grazed pasture previous year
*longer lifespan in colder weather
b) ''Larval numbers decline in the spring'':
*heavy mortality of overwintered L3 (food reserves soon depleted as temperatures rise)
*diluted by spring grass growth
''Host infected at turnout, patent infections develop and pasture contaminated'':
*stock ingest remaining overwintered L3
*strongyle eggs passed out with faeces onto pasture