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Poultry feed could be a potential vector in the transmission of pathogens to the poultry. The processing facilities of poultry products can be contaminated by carrier or infected carcasses which lead to transmit of pathogens through the food chain to human. There is a correlation between the presence of Salmonella in poultry feed and their isolation on poultry meet. On the other hand, over 50% of all traceable human cases of salmonellosis have been associated with the consumption of eggs and other poultry products. The need for biological safety of the poultry products initiated a worldwide search to find an economically efficacious feed management strategy, which decontaminates feed, and meanwhile, would be putatively beneficial for the gut microbiota and have no negative impact on the animal welfare, physiology, performance, nutrient digestibility and consumer health (Chapter 1).
In Chapter 2, a summary of the literature on different types of feed management strategies is given. The main objective of the present thesis was to investigate the effects 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 acid supplementation (63.75% formic acid, 25.00% propionic acid and 11.25% water) and their interactions on hygienic status of broiler feed, nutrient digestibility and bacterial composition and activity in gastrointestinal tract of broiler chicks.
The detailed information on the main aims and hypotheses of the present study can be found in Chapter 3.
In Chapter 4 and 5, the effects of different thermal treatments including pelleting (P), long-term conditioning at 85°C for 3 minutes (L), or expanding at 110°C (E110) and 130°C for 3-5 seconds (E130) without or with 0.75 and 1.5% organic acids supplementation on hygienic status of feed, performance, nutrient digestibility, gastrointestinal microbiota and organ weights of broilers are investigated an disccused.
In total, 960 one-day-old broiler chicks were randomly assigned to 8 replicates using a 3 × 4 factorial arrangement. Performance variables were determined, and the relative organ weights, ileal and total amino acid (AA) digestibilities were measured at d 35. Also, at d 35, bacterial cell numbers in the crop, ileum and caecum, and bacterial metabolites in the crop, gizzard, ileum and caecum were determined.
The organic acids inclusion linearly improved feed efficiency in the first week (P ≤ 0.05). The acid inclusion levels and thermal treatments had no significant effect on the performance variables at later intervals of the growing period. The inclusion of organic acids had a quadratic effect on total and ileal digestibility of isoleucine (P ≤ 0.05); while it had no significant effect on the ileal and total digestibility of other AA and nutrients. The inclusion of 1.5% organic acids increased cell numbers of all clostridial clusters in the crop. The organic acids supplementation increased the propionic acid concentration in the crop and gizzard whilst there was a decrease in lactic acid concentration. In the ileum, the 0% organic acids group had the highest numbers of Lactobacillus spp. and enterobacteria. Inclusion of 1.5% organic acids increased ileal acetate concentration. The L group showed the lowest ileal AA and crude protein digestibility. The relative weights of jejunum and small intestine were significantly higher in the E130 group compared to P and L (P ≤ 0.05).
Increasing the feed processing temperature led to an increase of lactobacilli in the crop and ileum, while clostridia and enterobacteria seemed unaffected. Similarly, lactate concentrations increased in the ileum, but short chain fatty acids remained identical.
In the crop, an increase for acetate was found for the E130 group compared to all other thermal treatments. In conclusion, the results of the present thesis demonstrated that the applied thermal and organic acids treatments were efficient strategies in order to hygienize broiler feed. The long-term thermal conditioning might decrease the ileal nutrient digestibility, while pelleting and expansion, without or/and with organic acids supplementation, seemed to be less critical. While expansion increased lactobacilli and lactate in the crop and ileum, organic acid addition remarkably influenced bacterial composition and activity in the crop. Taking into account all the observed effects of applied thermal and organic acids treatments on the microbiota of gastrointestinal tract, the evaluated treatments in the present study might have positive effects on the bacterial composition and activity of the upper gastrointestinal tract in broiler chicks that might offer interesting perspectives to achieve a better control of intestinal bacterial colonization in poultry. These indicate the potential of expansion process and organic acids addition for the hygienization of broiler feed (Chapter 6).