The gastrointestinal endoparasites are one of the great sanitary problems in sheep production in Brazil. Economical losses caused by decrease in the production, increase in prophylaxis costs, as well as increase in the tax of mortality of the animals are influenced seriously by gastrointestinal endoparasites. Traditionally, the control of these endoparasites are based on exclusive use of anthelminthic or associate to management of pastures. Although this practice has been efficient in the control of parasitism, it caused the appearance of anthelminthic resistance. Results of several researches indicate the need of alternative strategies of control of infections by endoparasites to be developed. One of the proposals is to develop animals genetically resistant to infection by gastrointestinal endoparasites and their effects. This would contribute so much to reduce the contamination of the pastures, as to reduce the anthelminthic treatment number, delaying the resistance development and reducing the production costs. The objective of this work was to obtain variance components for sheep resistance to the infection by  gastrointestinal endoparasites under conditions of natural infection. 

L. M Nieto, E. N Martins, F. AF Macedo, E. S Sakaguti, A. I Santos

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 13, , 13.39, 2002
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