The effects of pathogen challenges on the performance of naïve and immune animals: the problem of prediction

Abstract

Predictive frameworks for performance under both physical and social stressors are available, but no general framework yet exists for predicting the performance of animals exposed to pathogens. The aim of this paper was to identify the key problems that would need to be solved to achieve this. Challenges of a range of hosts by a range of pathogens were reviewed to consider reductions in growth beyond those associated with reductions in voluntary food intake (VFI). Pair-feeding and marginal response studies identified the extent and mechanisms of how further reductions in growth occur beyond those caused by reduced VFI. Further reductions in growth depended on the pathogen, the host and the dose and were time dependent. In some instances the reduction in VFI fully explained the reduction in growth. Marginal response experiments showed increased maintenance requirements during exposure to pathogens, but these were different for specific amino acids. There were no clear effects on marginal efficiency. Innate immune functions, repair of damaged tissue and expression of acquired immunity caused significant but variable increases in protein (amino acid) requirements. More resistant genotypes had greater requirements for mounting immune responses. The partitioning of protein (amino acids) was found to be different during pathogen challenges. Prediction of the requirements and partitioning of amino acids between growth and immune functions appears to be a crucial problem to solve in order to predict performance during pathogen challenges of different kinds and doses. The problems of accounting for reductions in performance during pathogen challenges that are described here provide a useful starting point for future modelling and experimental solutions.Keywords: diseases, energy, growth, pathogens, protein IntroductionPredicting the effects of physical (Black et al., 1986;Wellock et al., 2003a), social (Wellock et al., 2003b and infectious (Black et al., 1999) stressors on performance is important for guiding future management, genetic selection and experimental strategies. No general model exists that predicts growth and performance of different host genotypes, when given access to different kinds of foods and challenged by pathogens. The aim of this paper was to characterise reductions in growth during exposure to different kinds and amounts of pathogen that were not caused by a reduction in voluntary food intake (Sandberg et al., 2006). This allowed for the main consequences of pathogen challenges that would need addressing in a predictive framework of growth to be identified.There is no general agreement on the overall problems that need solving in order to predict growth during pathogen challenges (Black et al., 1999; Coop and Kyriazakis, 1999;Kyriazakis, 2003;Powanda and Beisel, 2003). A general comprehensive model can provide a clearer background for the design of future experiments, and help improve our current understanding of the interactions between pathogen challenge, the host and its nutrition. To achieve t...

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