Abstract
The poultry sector provides a major contribution to the world food supplies and its meat and egg production is expected to increase sharply in the next ten years, leading to poultry becoming the most widely consumed meat. Hence, the health of broiler chickens is of great importance, however, the current
... read more
ban on preventive treatment of antimicrobials has led to an increase in intestinal health problems in poultry. This urges for alternative strategies to improve health of broiler chickens. Young chickens are more susceptible to infectious diseases than adult ones since the adaptive immune system is not fully developed yet. Therefore, strategies should aim at increase of resistance to pathogens early in the life of chickens. At that stage, the immune responsiveness of chickens to invading pathogens relies on the innate immune system and natural killer (NK) cells, abundantly present within the intestinal intraepithelial lymphocyte (IEL) population, are among the first to respond. The aim of this thesis was to investigate stimulation of immune responsiveness, modulation of intestinal microbiota and the interaction between these by nutritional supplementation in order to increase the resistance and consequently improve the health of young broiler chickens.
For this purpose, number and functions of natural killer (NK) and T cell subsets in the intestine and other tissues of broiler chickens were assessed and acquired insights used for subsequent studies pertaining modulation of these cells. Furthermore, the interaction between the immune system and intestinal microbiota in young broiler chickens was investigated by early exposure to adult-derived microbiota. This showed to accelerate the maturation of the intestinal microbiota paralleled by increased NK cell responsiveness. Then, the potential of selected nutritional strategies to modulate immune responsiveness and microbiota composition was investigated. Nutritional compounds were consecutively screened for enhanced activity of NK cells in vitro, and evaluated for safety during embryonic development in ovo and impact on performance traits in vivo. Based on these results, two nutritional strategies were selected for further investigation that showed potential to stimulate immune responsiveness directly and indirectly through modulation of the intestinal microbiota. Furthermore, a significant role for NK cells in the immune response to Salmonella enterica serotype Enteritidis (SE), an important intestinal pathogen in chickens, was recognized. Finally, nutritional supplementation resulted in increased resistance to SE infection in young broiler chickens by stimulation of NK cell responsiveness, modulation of intestinal microbiota as well as the interaction between these. In conclusion, the studies described in this dissertation contribute to the development of alternative strategies to increase the resistance of young chickens and consequently, to improve the health of chickens.
show less
