The effects of different thermal treatments and organic acids levels in feed on nutrient digestibility and gut microbiota in broilers

Thermal treatment of feed has an impact on the feed hygiene, while simultaneously might affect feed digestibility, subsequent nutrient availability for the gut microbiota and the performance of broilers. Organic acids supplementation might conserve feed from subsequent contaminations and may simultaneously affect gut function, gut microbiota and the feed digestion process. However, the interactions of different thermal processes and organic acid levels have not been investigated to date. Despite a promising nutritional effect, the interaction of thermal processing methods and the addition of organic acids have not been widely studied and there is a little information assessing the effect of organic acid supplementation, solely or/and in combination with thermal processing, on gut microbiota, performance and particularly feed digestibility in broilers. Therefore, the aim of the present dissertation was to evaluate the effect of different thermal treatments including pelleting, long-term conditioning at 85°C for 3 minutes, or expanding at 110°C and 130°C for 3-5 seconds without or with 0.75 and 1.5% organic acids supplementation (63.75% formic acid, 25.00% propionic acid and 11.25% water) and their interactions on: 1. Hygienic status of broiler feed 2. Bacterial composition in crop, ileum and caecum of broilers 3. Bacterial metabolism in crop, gizzard, ileum and caecum of broilers 4. Relative weights of the proventriculus, gizzard, duodenum, ileum, caecum and pancreas 5. Nutrient digestibility of broiler feed 6. Performance variables of broiler chicks The results of the present thesis have been reported and described in the published manuscripts of the following chapters (Chapter 4 and Chapter 5).