Genetically resistant sheep avoid parasites to a greater extent than do susceptible sheep

Livestock breeding programmes have created resistant (R) and susceptible (S) sheep that differ in their ability to control parasites through their immune function but potentially also their grazing behaviour (i.e. parasite avoidance). Using the Perendale genetic lines, we tested the hypothesis that...

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Bibliographic Details
Published in:	Proceedings of the Royal Society. B, Biological sciences Vol. 274; no. 1620; pp. 1839 - 1844
Main Authors:	Hutchings, M.R, Knowler, K.J, McAnulty, R, McEwan, J.C
Format:	Journal Article
Language:	English
Published:	London The Royal Society 07-08-2007
Subjects:	Animals Behavior, Animal Eggs Forage Genetic Predisposition to Disease Grazing behavior Grazing Behaviour Herbivores Larvae Nitrogen Parasite Avoidance Parasite Resistance Parasites Parasitic Diseases, Animal - genetics Parasitic Diseases, Animal - parasitology Parasitism Sheep Sheep Diseases - genetics Sheep Diseases - parasitology Sward Time Factors
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Summary:	Livestock breeding programmes have created resistant (R) and susceptible (S) sheep that differ in their ability to control parasites through their immune function but potentially also their grazing behaviour (i.e. parasite avoidance). Using the Perendale genetic lines, we tested the hypothesis that R-sheep avoid parasites more effectively, reducing their parasite exposure/challenge, compared with S-sheep. However, in grazing systems, parasite-rich areas are also forage rich, suggesting that parasite avoidance behaviours are associated with nutritional penalties. We first created a naturally heterogeneous sward structure of gaps and tussocks and then used focal behavioural observations to quantify the sward selection of R- and S-sheep. Tussock swards were more nitrogen rich (41%), offered increased forage intake rates (32%) and contained 17 times more parasite larvae than gap swards. All the animals avoided grazing the tussock swards. However, the R-sheep grazed the tussock swards to a lesser degree than the S-sheep. We conclude that selection for genetic resistance has resulted in animals that, despite being well armed to fight parasitism through improved immune function, adopt parasite avoidance strategies with associated nutritional disadvantages. This experiment highlights the role of host behaviour in the control of parasitism and suggests that animals can be bred to avoid disease.
Bibliography:	istex:5BD504F2CE4EC92F19307631F2D1D9253D6660B2 ArticleID:rspb20070398 ark:/67375/V84-K2F3MHTJ-V href:1839.pdf
ISSN:	0962-8452 1471-2954
DOI:	10.1098/rspb.2007.0398