The significance of inhibition in the parasitic development of abomasal nematodes in New Zealand sheep

Abstract

Extract

Infective larvae of Haemonchus contortus when ingested by sheep normally undergo development through a series of moults to become sexually mature, adults, a process that takes 14 to 15 days (Veglia, 1915). In some circumstances, however, such larvae may become arrested in their development at an early fourth larval stage 3 to 4 days following ingestion (Blitz and Gibbs, 1971). A similar phenomenon of arrested or inhibited development has also been recorded in Ostertagia circumcincta and Trichostrongylus axei infections in sheep; in the former again occurring at an early fourth stage, (Sommerville, 1953, 1954) and in the latter at a loosely defined “fourth larval stage” (Reid and Armour, 1972).