Influence of health on feed efficiency
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The concept of improved health leading to better feed efficiency is a concept that makes intuitive biologic sense but in reality is difficult to quantify. This is due to the complex interaction between the pig’s immune response, pathogens that cause disease, and the external environment where the pig is raised. Mortality causes a direct effect on feed efficiency, since pigs that die consume feed but do not contribute weight gain in the calculation of feed efficiency. Further influence of health on feed efficiency arises from chronic immune system stimulation that affects composition of gain. Since lean tissue gain requires less feed per unit of gain in comparison to fat tissue, healthier pigs that increase lean tissue gain at a greater rate than fat tissue gain will be more feed efficient. Evidence indicates that in multi-site pig production systems, chronic immune stimulation is reduced due to age segregation, leading to less pathogen transmission across age groups and via the environment from batch to batch. Unfortunately, multi-site pig production systems have not eliminated all pathogens and clinical disease in pig populations. The predominant pathogen specific effect of health on feed efficiency in these systems is produced by mortality. A lower magnitude of health influence on feed efficiency is mediated through metabolic alterations of survivors. This appears to be the result of the dynamic nature of the pig’s immune system mitigating the influence in the survivors. Furthermore, it appears that non-specific healthenhancing factors such as biosecurity and sanitation protocols to prevent lateral transmission of infectious pathogens and reduced environmental contamination and result in considerable improvements in feed efficiency.