Soybean meal is world wide used as an ingredient of poultry diets, due to both its high quality and quantity of protein content. Meanwhile soybean meal contains relatively high levels of soluble carbohydrates, known as oligosaccharides (SMO) and polysaccharides (SMP). SMO and SMP can not be digested by digestive enzymes and tend to reduce the available energy in the diet, therefore behaving as an anti-nutritional factor. However, SMO and SMP can be utilised by intestinal microflora. Thus they may act as prebiotics. They may affect gut microbial community population consistent, and promote the proliferation of gut mucosal cells including natural antibodies, especially, when SMO and SMP are used in broilers’ diets during the early stage of post-hatch. As a result, SMO and SMP may affect the development of the gastrointestinal tract and furthermore on productivity. They may stimulate the growth of gut lactic acid-producing bacteria (LAB) and promote immune competence ability. To test the prebiotic and immune stimulating role of SMO and SMP on broiler chickens several experiments have been made. One in vitro experiment was made to study kinetics of the in vitro fermentation. Caecal contents were used as source of inoculum. Three animal trials (in which SMO and SMP were used as diet additives in broiler diets of the first two weeks of post-hatch) are described in this thesis. The results showed that non-digestible carbohydrates were fermented by caecal contents microbial community of broiler chickens in vitro. SMO, SMP, AMO, AMP, and STA could significantly stimulate caecal contents bacteria activity and lead to shift of caecal contents microbial community in some extent. SMO produced the lowest ammonia nitrogen and highest butyric acid in these fermentable carbohydrates after fermentation. When the diet of the first two weeks were diluted by 1% SMO and 0.5 % SMP, respectively, dietary SMO and SMP didn’t affect the development of intestinal length and relative weight. However, dietary SMO and SMP decreased the villus size, and tended to increase microvilli density on villus surface; dietary SMO significantly increased LAB population in caecal contents both in healthy birds and the birds infected with Eimeria tenella; dietary SMO and SMP enhanced cellular but did not affect humoral immune response followed by vaccination; SMO and SMP led to an increase in immunoglobulin A, M and Y positive plasma cells (IgA +, IgM + and IgY+) in the caecal lamina propria both in healthy birds and the birds infected by E. tenella; SOM and SMP led to feed restriction during its use in diets as an additive, but a complete compensatory growth took place after SMO and SMP were withdrawn from diet.
In conclusion, water-soluble carbohydrates (SMO & SMP) had prebiotic and immune stimulating effects on broiler chickens when used as feed additives in broiler diets in the early stage post-hatch period, and it may have beneficial effects on certain microbiological and immunological promotion within the GIT, might therefore be suitable additives for the promotion of GIT health. Meanwhile, if can used as a safety feed restriction additive in the diet of broiler chickens.
Keywords: soy water-soluble carbohydrates, fermentation kinetics, intestinal morphology, caecal contents lactic acid bacteria, immunoglobulin, feed restriction, broiler chickens.