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1. What is the length of the prepatent period of typical roundworms and how can the prepatent period be used to advantage?
2. What are the two most important factors for susceptibility to breech strike?
3. How many species of lice occur on sheep in Australia?
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This is the time taken for infective larvae, eaten by a sheep grazing pasture, to develop to adult worms in the gut, mate and start laying eggs, which appear in dung. The time depends on the worm species with barber’s pole worm completing this period in a minimum time of 18 days under ideal conditions. Most scour worms take about 21 days.
Therefore, little, if any, worm egg contamination of pastures will come from sheep in the pre-patent period from a few days after they have been given an effective drench that kills 98% or more of the worms present. Allow sheep to graze up to 21 days in barber’s pole worm areas and to 30 days in southern scour worm areas. This is a principle used in ‘Smart grazing’.
Research over many years has shown that the two most important factors affecting breech strike risk are breech wrinkle and dag.
Three. The sheep body louse (Bovicola ovis, formerly called Damalinia ovis) is a pale yellow insect 1.5 to 2 mm long with brown transverse stripes on the abdomen and a broad, red-brown head (Figure 1). It is a chewing louse and feeds on skin scurf, lipid and sweat gland secretions, superficial skin cells and skin bacteria (Sinclair et al. 1989). Males are smaller than females and have more pointed abdomens.
Sheep are also host to two other species of lice. The sucking lice feed on blood, have long thin heads and appear bluish in colour: the face louse, Linognathus ovillus, occurs mainly on or close to the face, and the foot louse, Linognathus pedalis, is found on the legs and on the scrotum in rams.