Parasitology

Research Article

The role of nematode parasites in Soay sheep (Ovis aries L.) mortality during a population crash

F. M. D. Gullanda1

a1 Large Animal Research Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ

Abstract

In early 1989, two-thirds of the Soay sheep population on St Kilda died over 12 weeks. Post-mortem examinations revealed emaciated carcasses and considerable nematode burdens, with protein-energy malnutrition as the probable cause of death. Haematological and blood biochemical changes in the sheep, as well as fecundity of gastrointestinal nematodes, suggested the hosts were immunosuppressed. In parallel, laboratory experiments in which Soay sheep on a high plane of nutrition were artificially infected with Ostertagia circumcincta, showed no clinical signs or mortality when supporting worm burdens similar to those recorded in dead sheep on St Kilda. Anthelmintic treatment of a group of animals increased daily survival rates in ewes and male lambs, although treated animals became re-infected as the ‘crash’ progressed. It is suggested that parasites contribute to mortality in malnourished hosts, exacerbating the effects of food shortage.

(Received January 30 1992)

(Revised April 11 1992)

(Accepted April 28 1992)

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