title: Effects of chronic infection with Trichostrongylus vitrinus and immune suppression with corticosteroid on parasitological, immune and performance variables in crossbred meat lambs.
abstract: The effects of, and interactions between chronic Trichostrongylus vitrinus infection and immune suppression with methylprednisolone were investigated for a period of 112 days in a grazed flock of 176 crossbred meat lambs. Worm egg count of non-immune-suppressed lambs increased rapidly from days 21 to 42 post-initial infection, and then steadily declined. Infection was associated with significantly decreased fat depth, eye muscle area and cold carcase weight, and increased circulating anti-T. vitrinus IgG and IgA. Immune suppression led to sustained increases in WEC, and significantly greater worm count, liver weight, fat depth and carcase dressing percentage, and significantly reduced IgG and IgA anti-T. vitrinus titres, lymphocyte counts, adrenal weight, eye muscle area and cold carcase weight. Both infection and immune suppression were associated with significant body weight reductions. Only 39% of reduced growth rate due to infection was attributable to the host immune response to T. vitrinus.
authors.affiliation: South Australian Research and Development Institute, Urrbrae, South Australia 5064, Australia; Animal Science, School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2350, Australia. Electronic address: pblackb2@myune.edu.au.
authors.forename: P J
authors.initials: PJ
authors.lastname: Blackburn
authors.affiliation: South Australian Research and Development Institute, Urrbrae, South Australia 5064, Australia; Animal Science, School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2350, Australia.
authors.forename: I H
authors.initials: IH
authors.lastname: Carmichael
authors.affiliation: Animal Science, School of Environmental and Rural Science, University of New England, Armidale, New South Wales 2350, Australia.
authors.forename: S W
authors.initials: SW
authors.lastname: Walkden-Brown
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002908:Chronic Disease; D005260:Female; D007165:Immunosuppression Therapy / Q000662:veterinary; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008297:Male; D008775:Methylprednisolone / Q000494:pharmacology*; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology* / Q000469:parasitology; D014253:Trichostrongylosis / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D014254:Trichostrongylus / Q000502:physiology*
chemical_list: D007166:Immunosuppressive Agents; D008775:Methylprednisolone
keywords: Corticosteroid; Immune response; Immunity cost; Infection cost; Sheep; Trichostrongylus vitrinus