Internal phase of large strongyles larval development encompasses a somatic migration whereas those of small strongyles burrow into the glands in the caecum and colon and become encysted with no further migration.
Large strongyles larvae migrate widely within the host through extra-alimentary tissues with a minimum of 6 month prepatent period (Kaplan 2004).
Large strongyles have large buccal capsules which they attach to the intestinal mucosa pull out a plug of tissue absorb the host cells crack the blood vessels and suck blood feed on the mucosa and consume blood (Levine 1980).
At necropsy the crater-like ulcers caused by large strongyles are often more numerous than the worms suggesting that they move periodically to new sites of attachment (Andersen et al.
Clinical Signs: The acute signs related with large strongyles are due to migrating larvae and are seen during the first few weeks after infection.
The percentage of large strongyles viable eggs was lowest in winter but maximum in May and remained high throughout the summer (Ogbourne 1975).