The seasonal occurrence of inhibited abomasal nematodes in young sheep

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Abstract
Extract The susceptibility of many trichostrongylid nematodes, particularly those inhabiting the abomasa of domestic ruminants, to inhibited parasitic develolpment is well known. In most cases development is arrested at a precise point for a given species, usually occurring shortly before or after a moult ( Rogers and Sommerville, 1969 Blitz, N. M. and Gibbs, H. C. 1971. Morphological characterization of the stage of arrested development of Haemonchus contortus in sheep. Can. J. ZooL., 49: 991–995. [Google Scholar] ). Of the abomasal parasites of sheep, inhibition in Haemonchus contortus and Ostertagia circumcincta occurs at the early fourth stage ( Blitz and Gibbs, 1971 Blitz, N. M. and Gibbs, H. C. 1972a. Studies on the arrested development of Haemonchus contortus in sheep. I. The induction of arrested development. Int. J. Parasit., 2: 5–12. [Google Scholar] ; Sommerville, 1953 Blitz, N. M. and Gibbs, H. C. 1972b. Studies on the arrested development of Haemonchus contortus in sheep. II. Termination of arrested development and the spring rise phenomenon. Int. J. Parasit., 2: 13–22. [Crossref] [Google Scholar] , 1954 Brunsdon, R. V. 1970. Seasonal changes in the leveland composition of nematode worm burdens in young sheep. N.Z. Jl agric. Res., 13: 126–148. [Taylor & Francis Online], [Web of Science ®] [Google Scholar] ) and in Trichostrongvlus axei at a more loosely defined “fourth” larval stage ( Reid and Armour, 1972 Brunsdon, R. V. 1973. Inhibited development of Haemonchus contortus in naturally acquired infections in sheep. N.Z. vet. J., 21: 125–126. [Taylor & Francis Online] [Google Scholar] ).