الفهرس 
Chapter 1 – General introductionOnly 14 pages are availabe for public view
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Abstract
Broilers have high dietary requirements for protein as a major constituent of the biologically active compounds in the body and a vital nutrient for growth. In addition, protein and essential amino acids are essential for antibody formation and a well-functioning immune system, however protein is one of the most expensive nutrients in poultry diets. Therefore, considerable attention is being given to optimize (minimize) crude protein (CP) levels in poultry diets, including by applying the ideal protein concept (IP), which represents essential amino acid (AA) requirements as a ratio to lysine leading to an ideal dietary AA profile. However, since AA supplementation has been shown to improve resilience to sub-clinical pathogen exposure, the assumed generality of the IP concept may be challenged. The aim of this project was to investigate the effect of AA supplementation on resilience of broiler chickens to sub-clinical health challenges using IP-based rationing as the starting point. The results shows that AA supplementation to IP-formulated standard or lowered protein diets did not improve resilience to sub-clinical enteric challenge but reduced bird performance. This reduced performance may have been due to reduced ileal digestibility of AA, resulting in increased excess protein and thus enhanced proteolytic fermentation. Lowering dietary crude protein (CP) while maintaining the IP concept and glycine requirements reduced bird performance, which could indicate the inability to apply the IP concept, particularly during the starter phase. Exposing birds at placement to reused litter in which Salmonella spp., C. perfringens and Eimeria spp. were below detection level, improved bird performance, indicating that reused litter might be a source of recycled nutrients and direct-fed microbiome rather than a source of pathogen challenge. Therefore, before employing reused litter exposure, detailed litter characterization is required to optimize study design, including origin description, duration and storage condition between collection and usage.