Soutenance de thèse de Samuel Jansseune

La soutenance sera en anglais et aura lieu à l’université de Wageningen et sera diffusée en direct. 
 
Elle a été réalisée avec un co-encadrement scientifique entre l’équipe GeMS de GABI et le département de nutrition animale de WUR.

Encadrants : Marie-Hélène Pinard-van der Laan et Wouter Hendriks
Jury :
Prof. Dr V. Berthelot, AgroParisTech, Palaiseau, France
Dr E. van der Hoeven-Hangoor, Cargill Animal Nutrition, Velddriel
Prof. Dr G.P.J. Janssens, Ghent University, Belgium
Dr P. Moquet, MiXscience, Bruz, France
Dr J.W. Schrama, Wageningen University & Research

Résumé :
Probiotics (beneficial live micro-organisms, often bacteria), and more recently postbiotics (dead beneficial micro-organisms and/or compounds produced during their growth), have received increasing interest by feed producers to improve the growth and health of broiler chickens. This thesis describes research to determine the effects of the heat process to produce a postbiotic (Post) from a probiotic (Pro) on the composition and the way both affect the growth and physiology of broilers.
In the first laboratory experiment, the composition of small molecules (= metabolome) of Pro and Post additives was assessed and what impact the heat treatment has. It was shown that the heat treatment to produce Post had minor effects on the metabolome. Some of the identified molecules are known in the scientific literature to influence immune processes and reduce growth of harmful (pathogenic) bacteria. The antibacterial effect was, therefore, tested but found to be absent in both Pro and Post. Next, the effect of Post on an immune cell (macrophages) of chickens was investigated. Also, for Post, the macrophages were treated with different doses (null, low medium and high) of a component (lipopolysaccharide = LPS) from pathogenic bacteria. On its own, the LPS increased the inflammatory response of the macrophages which was increased by Post and depended on the LPS dose (greater increase at medium and high doses compared to the increase at null and low doses). 
To assess effects of Pro and Post in broiler chickens, three experiments were conducted under practical housing conditions (= in vivo). The first experiment evaluated if the composition of the diet (standard v.s. growth-depressing challenge diet) can influence the way Pro and Post work. Both feed additives contained their commercial carriers (= mixture used to carry an additive as a dry powder). Pro and Post increased growth and modified the caecal bacterial population (= the microbiota) only in broilers fed the challenge diet. In the second experiment, the reproducibility of this growth promoting effect of Pro and Post with their carriers was evaluated using two different challenge diets. Unlike the first experiment, Pro and Post did not improve broiler growth showing that the previously found results were not reproducible. The third in vivo experiment had two aims. Firstly, it investigated if the commercial carriers change the way Pro and Post affect the broiler chicken. Second, it assessed if expression of genes in the blood, small intestinal segments (jejunum and ileum) and in an immune organ of the caeca (the tonsils), as well as on the microbiota and metabolites in ileal and caecal digesta are affected by Pro and Post. The results showed that broiler growth was improved by Pro but not by Post, whilst the presence of their commercial carriers reduced and increased growth, respectively. Pro (without its carrier) lowered inflammation in the jejunal and caecal tonsil tissues, while Post had very limited and unclear effects. The data of the latter third experiment were further analysed to identify parameters associated with broiler growth. The gene expression data indicated that broilers reaching a greater body weight at 35 days had reduced inflammation in jejunal tissue.
In conclusion, for Pro without carrier, and for Pro and Post with carrier to be beneficial for broiler growth, challenging conditions are required. The carriers changed the effects of Pro and Post. Pro without carrier had a beneficial effect on growth and lowered intestinal inflammation. This effect was likely due to the viable cells in Pro and/or components that are degraded by the heat treatment to produce Post from Pro. The metabolites in Pro and Post may have limited effects in broilers. Furthermore, lowering intestinal inflammation may allow for improvements in growth and health in broiler production.