Author:

Abstract:

Since the early 1960s, the global production of poultry meat per capita has undergone a remarkable sixfold increase. Chicken meat, responsible for 90% of the global poultry production, has transitioned from a niche food product to a readily accessible and cost-effective source of protein-rich, low-fat meat characterised by a favourable fatty acid profile. At present, the poultry sector is characterised by vast production volumes, low margins, fine-tuned manipulations, and investments based on well-considered scientific decisions. One of the main strategies to optimise economic profit and ensure sustainable intensification, is the increase of feed efficiency through intensive selective genetic selection and improved nutritional management. This rigorous selection of performance traits, such as feed conversion rate, has caused substantial adaptations in the gastrointestinal physiology of the contemporary broiler and resulted in decreased maturity at slaughter age, and affected size and histological characteristics of digestive organs at all ages. The negative consequences of this intensive genetic selection are substantial and include, amongst others, an impaired immune system and a decreased nutrient absorption in the modern broiler, rendering the important balance between nutrients, microbiota and intestinal health even more delicate. For many years, the use of antibiotic growth promotors (AGPs) in the broiler industry successfully mitigated this problem. However, constraints imposed on AGP use due to concerns regarding antimicrobial resistance, caused problems like dysbiosis to resurface. In response to the increasing constraints on AGP use, the quest for alternative products to regulate the intestinal health and modulate the microbiome has become an imperative necessity. However, the feasibility of implementing a singular, economically viable substitute for AGPs appears unlikely. Instead, it has become increasingly evident that addressing the specific challenges encountered in the intestinal health of modern broilers requires the adoption of a multipronged approach including biomarkers, prebiotics and phytobiotics. This thesis consists of three independent research projects, each linked to the interplay between intestinal health, microbiota and nutrition in poultry, and focused on unravelling a small piece of the complex puzzle. In Chapter 3, the potential of lignin oils and derived phenolic monomers as phytobiotics was assessed using in vitro antibacterial assays. Lignin is the most abundant source of renewable aromatics on earth. However, due to its inherent complex and heterogeneous nature, lignin is often considered a waste product and is usually combusted for heat production as low-grade fuel. In pursuit of improving the sustainability and competitiveness of biorefineries, the valorisation of lignin is essential. In this study, we aimed to evaluate the antibacterial activity of lignin-derived refined oils (RLOs) obtained from softwood (pine) and hardwood (poplar) through reductive catalytic fractionation (RCF). By using different substrate material and different metal-containing catalysts to selectively keep (Pd/C) or remove (Ru/C) the hydroxyl-functionality in the sidechain of the resulting monomers, lignin oils with different molecular compositions were obtained. Antibacterial activity was assessed using three Gram-negative (Avian Pathogenic Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica) and three Gram-positive bacterial strains (Staphylococcus aureus, Enterococcus cecorum, and Lactobacillus salivarius). Absence of the hydroxyl group on the alkyl chain was observed to be crucial for antibacterial activity. This was confirmed by the fact that RLOs produced using an Ru/C catalyst showed antibacterial activity against Gram-positive bacteria, in contrast to those produced with a Pd/C catalyst. Five lead molecules, present in the RLOs, were selected and also included in the antibacterial assays. Three lignin-derived lead molecules with moderate but significant antibacterial properties were identified: 4-propylguaiacol, 4-propylsyringol, and methylparaben. In Chapter 4, we aimed to evaluate another potential alternative to AGPs: wood-derived xylo-oligosaccharides (XOS). The objective of this research was to investigate the potential of XOS prepared by enzymatic hydrolysis of beechwood xylan as a prebiotic feed supplement for broilers. A pilot study was conducted to explore the optimal XOS fraction profile by in vitro fermentation. Subsequently, a semi-continuous enzyme membrane reactor was used, allowing for the production of tailored XOS in large quantities. Then, an in vivo experiment was performed to explore the potential of XOS as a prebiotic feed supplement by investigating growth performance, feed conversion ratio, caecal short and medium chain fatty acid (SCFA and MCFA) concentration, and microbiological composition of the caecal content of broilers. Results from the pilot study indicate that higher enzyme concentrations in the hydrolysis process yield a product that leads to a higher total SCFA-, MCFA- and butyric acid production during in vitro fermentation by caecal bacteria. Supplementation of the tailored XOS to the broiler diet (day 1 (d1)-d8 0.13% wt/wt XOS, d9-d15 0.32% XOS) resulted in higher Bifidobacterium counts, beneficial to the health of birds, on d11 and d15. Farm management and housing systems are known to have a significant influence on broilers and their intestinal development at an early age. In Chapter 5, a new concept to overcome some of the disadvantages of conventional hatcheries is explored: on-farm hatching. In on-farm hatching systems, broiler eggs are transported to the broiler house on day 18 of incubation (ed18). On-farm hatched chicks hatch in a low dust environment, are immediately exposed to light, and have instant access to nutrients and water. Previous studies reported that on-farm hatching systems provide birds with an improved intestinal health and a lower feed conversion rate; resulting in a reduced use of antibiotics. Although it is generally agreed that the intestinal health of on-farm hatched chicks is better, the causative factors remain largely unknown. To explore the effect of hatching system on intestinal development, a full factorial in vivo experiment was designed, taking into account commercial age (minus two days (D-2), D-1, D1 and D2) and hatching condition (hatchery-born, hatchery-born with Spectoliphen 100 treatment, and on-farm hatched using the NestBorn-system) as factors. To assess intestinal development, diamine oxidase (DAO) serum levels were measured. DAO, a highly active intracellular enzyme that is synthesized mainly by the intestinal mucosal cells, is generally used as an indicator for intestinal maturation and intestinal permeability (IP) in mammals and birds. Analysis of serum samples showed that serum DAO levels in hatchery-born chicks were significantly lower compared to their on-farm hatched counterparts on all four days, suggesting that the intestinal development in the latter took place earlier. However, the long-term effect was not explored in this study. An additional comparison between the hatching systems was made, not according to commercial age, but in reference to time of access to feed. In this comparison, no differences between the two groups were observed. Interestingly, in the hatchery-born chicks, no compensatory development of the intestines took place within the time span of this experiment. The effect of Spectoliphen 100 during the first days on the intestinal development and IP of chicks remains poorly understood and requires further investigation. In conclusion, the intricate interplay between intestinal microbiota, nutrition, and intestinal health in the poultry industry represents a multifaceted yet pivotal aspect of production. The complex balance between these factors makes it challenging to draw definitive conclusions from research, as various variables come into play, each with the potential to significantly influence outcomes. The need for comprehensive research on a wide range of microbiome-related topics, including prebiotics, probiotics, designer probiotics, and postbiotics, is essential. The development of effective methods for monitoring and promoting intestinal health is equally important, presenting the opportunity to enhance poultry production while upholding sustainability, animal welfare, and production efficiency. As we move forward, it is evident that this dynamic and evolving field holds the promise of transformative changes in the poultry industry, emphasizing the indispensable role of microbiota research in shaping its future.