• Higher field strength MRI may improve image quality and diagnostic accuracy. • There are few direct comparisons of 1.5 and 3 T MRI. • Theoretical doubling of the signal-to-noise ratio in practice was only 25 %. • Objective evidence of improved routine clinical diagnosis is lacking. • Other aspects of technology improved images more than field strength.
BackgroundBoth host genetic potentials for growth and disease resistance, as well as nutrition are known to affect responses of individuals challenged with micro-parasites, but their interactive effects are difficult to predict from experimental studies alone.Methodology/Principal FindingsHere, a mathematical model is proposed to explore the hypothesis that a host's response to pathogen challenge largely depends on the interaction between a host's genetic capacities for growth or disease resistance and the nutritional environment. As might be expected, the model predicts that if nutritional availability is high, hosts with higher growth capacities will also grow faster under micro-parasitic challenge, and more resistant animals will exhibit a more effective immune response. Growth capacity has little effect on immune response and resistance capacity has little effect on achieved growth. However, the influence of host genetics on phenotypic performance changes drastically if nutrient availability is scarce. In this case achieved growth and immune response depend simultaneously on both capacities for growth and disease resistance. A higher growth capacity (achieved e.g. through genetic selection) would be detrimental for the animal's ability to cope with pathogens and greater resistance may reduce growth in the short-term.SignificanceOur model can thus explain contradicting outcomes of genetic selection observed in experimental studies and provides the necessary biological background for understanding the influence of selection and/or changes in the nutritional environment on phenotypic growth and immune response.
Models that predict phenotypic responses from the interaction between genotypic descriptors and the environment are desirable both in the context of both animal production systems and evolutionary ecology. Nutrient availability is often related to the ability of a host to control an invading parasitic population and mounting an immune response is often associated with a nutritional cost. This cost is shown by the peripartuient break down of immunity (Houdijk et al., 2003) and reports of negative correlations between production and resistance traits (Rauw et al., 1998). The aim was to develop a model which is able to make predictions relating to the effects of resource allocation as determined by nutrition and genotype, on the course of microparasitic infection in farm animal hosts.
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