The response of supply organs of young broilers fed different nutritional levels

Nutritional broiler studies in general focus on the overall lifespan performance parameters, ignoring early development of supply organs (e.g. gastrointestinal tract, respiratory and cardiovascular systems) which are a determinate for growth of the demand organs (e.g. muscle, skeleton, adipose tissue) at a later age. The development pattern of supply organs has been described in research, however there is a lack of consensus between papers. Additionally papers that found effects of macro nutrients on early development are cofounded by their setup. Supplying the correct nutrients for optimal supply organ development will help the bird develop and maintain an optimal digestive and absorptive capacity, and could results in an optimal health status. Dietary energy is derived from three major nutrients: carbohydrates, fats, and amino acids, each of these goes through several digestion steps, which may be co-dependent or rate-limiting. First feed intake requires broilers to shift from lipid oxidation to glucose and starch oxidation and glycolysis. Starch digestibility is proven to be high compared to other nutrients, however the majority of its product, glucose, will be used for glycogen synthesis instead of immediate oxidation. This could be due to rate-limiting steps in the glycolysis of young broilers or lack of metabolic inter-mediates in the pathway. Compared to carbohydrates digestibility of fat is low at young age, however given that lipids are the primary energy source during embryonic development, it could be that these have an positive effect on supply organ development. Studies that have compared energy from carbohydrates to fat have shown positive effects of fat addition, however there were confounded due to the setup. Despite the fact that amino acids are required for protein accretion part of it is used for energy supply. Glutamate and glutamine have been indicated as main energy substrate for rapidly proliferating cells, such as enterocytes, supplying 2-oxo-glutarate for the citric acid cycle. Arginine is a novel pathway to consider as it supplies substrates that play a crucial role in the main parts of the metabolism. The effects of the branched chain amino acids (valine, isoleucine, leucine) on supply organ development is not known, they could be limiting the development as possible fourth limiting amino acid or in regulation of essential processes (e.g. TOR signaling, glucose uptake, tight junction transcription). In conclusion, the response of individual nutrients such as energy and amino acids on the development of supply organs at a young age is not fully understood. Therefore, the objective of this PhD will be to determine which nutrients are responsible for optimal supply organ development.