HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gross, W. B. Articles by Siegel, P. B. Search for Related Content PubMed Articles by Gross, W. B. Articles by Siegel, P. B.

Why Some Get Sick

Department of Large Animal Clinical Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Phone: (540) 552-2154; FAX: (540) 231-3713

P. B. Siegel

Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Correspondence: W. B. Gross

This paper reports factors that determine the susceptibility of individuals to bacterial, viral, and parasitic diseases and toxins, as well as their humoral and cell-mediated immune responses, Interactions of genotypes and environments are major factors in the allocation of resources to disease defense. These allocations are dynamic and vary throughout the life of an individual. Allocation of resources to defend against disease may occur at the expense of growth, feed conversion, or other factors. Furthermore, an individual cannot simultaneously have a strong defense against all disease agents. Virulence of infectious agents and host-pathogen relationships are also important factors in an individual's susceptibility. Since any individual's level of defense against a given agent is not constant, chance is also a factor, for exposure to a disease agent can occur when the individual's defense level is low or high.

Key Words: Chickens • diseases • environment • genetics • resource allocations