Observations are reported on the behaviour and longevity of infective cattle strongyle larvae in faecal pats and on pasture in south-eastern Queensland. Environmental conditions within the pat were favourable for the development of infective larvae at all seasons of the year except midsummer and midwinter. Larvae were distributed for the most part either in the pat or on pasture vegetation. Larvae migrated laterally from the pat for distances up to at least 3 ft, but usually not more than 1 ft, and these movements occurred only after suitable rain. At no time was a single mass movement of all larvae in the pat observed. If rainfall was continuous, migration was continuous, and when rainfall was alternated with periods of dryness, migration occurred in waves. Pats exposed in the summer remained a source of larvae for 5 months. This period was extended to 7–8 months with pats exposed in the winter. Larvae survived on pasture for up to 6 and 8 weeks respectively for these seasons of the year. Vertical migration on pasture was also observed.
A description of the development at 27�C. of Ceylonocotyle streptocoelium
(Fischoeder 1901) Nasmark 1937, a paramphistome from the rumen and
reticulum of sheep and cattle in Australia, is given in detail.
Eggs hatched after 16 days' incubation and miracidia penetrated the intermediate
host, a planorbid snail, Glyptanisus gilberti Dunker 1848, through the
mantle cavity. The development of the larval stages of the parasite within the
intermediate host was completed 34 days after infection, when cerariae were
secreted by snails.
Cysts of C. streptocoelium fed to sheep and cattle showed that flukes
reached maturity in the rumen in 48 and 56 days respectively. The life cycle
of the fluke, therefore, was completed in a minimum period of approximately
3.5 months under these conditions.
It was found that temperature had a marked effect on the rate of development
of larval stages within the molluscan intermediate host, the developmental
period at 20�C. being twice as long as that at 27�C.
The various stages occurring in the molluscan intermediate host are described
in detail.
The development of Paramphistomum ichikauiai Fukui 1922 is compared
with that of C. streptocoelium. The rate of development was found to be more
rapid than for C. streptocoelium under the same conditions. Eggs hatched
after 12 days incubation and cercariae were secreted from the intermediate
host, Segnitilia alphena Iredale 1943, 25 days after infection.
Flukes were found to reach maturity in sheep 49-51 days after cysts had
been fed. The eggs and intra-molluscan stages are similar in both species,
but the cercariae may be readily distinguished by anatomical differences in their
excretory systems. The life cycle in this species takes approximately 3 months
to complete under these conditions.
The molluscan intermediate hosts of the two species of amphistomes are
described and notes on their bionomics are given.
Fluctuations in populations of infective larvae of cattle strongyles on a naturally grazed calf pasture were studied for 2 years. Susceptible calves were introduced to the pasture each month to determine how host infection was influenced by the degree of pasture contamination as measured by the number of larvae recovered per pound of pasture. The most numerous larvae recovered at all seasons belonged to the Cooperia spp. group. Larvae of Trichostronqylus axei were abundant throughout the winter to early summer, but scarce during midsummer and autumn. Larvae of Haemonchus placei were most abundant during the late summer and winter, and those of Oesophagostomum radiatum occurred in relatively small numbers at all times. Gross peaks of abundance occurred during the summer and midwinter, when the rainfall was higher than at other periods of the year. Although greater numbers of larvae per pound of pasture were recovered during the winter than during the summer, host infections were higher during the summer. This inverse relationship between the number of larvae and host infection is believed to be a result of a greater intake of pasture during the summer. An assessment of the degree to which a pasture may be dangerous therefore involves consideration not only of the number of larvae present, but also of the state of the pasture. Estimates of the daily intake of larvae by susceptible animals, allowed to graze for a restricted period and then examined at necropsy, ranged between 19 and 31 655 larvae.
A new technique for the recovery of Trichostrongyle larvae from soil and pasture samples is described.The technique is based on the difference in density of larvae and debris under the influence of a stream of water flowing upwards at a gradually decreasing flow rate.The results from trials with known numbers of larvae gave an average recovery of 74% from pasture, and of 78% from soil.
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