Broiler flocks become frequently asymptomatically contaminated by the enteric bacteria Salmonella sp. and Campylobacter sp. which are human pathogens. Among the strategies developed at farm level to reduce the incidence of these pathogens, some lactic acid bacteria have been shown to be interesting because of their antimicrobial activity and their stimulatory properties on the immune system of poultry. The aim of this thesis was to select bacteria with antagonistic activity against Salmonella or Campylobacter, and to improve their inhibitory effect by the combination with enzymes of polysaccharidase type. The first step of the thesis was an epidemiological study carried out in the Walloon region in order to determine the contamination way of broilers by Campylobacter in free range production. Results showed that the major way of contamination is the open-air range to which the animals have access during the rearing period. A preventive treatment of the open-air range and the straw litter with an antagonistic strain in combination with an enzyme seems thus to be suitable in this case. The second step of the work aimed at the selection of a xylanase for using as a dietary additive in combination with an antagonistic bacterial strain against Salmonella. Four xylanases were studied in vivo for their effect on growth performances of broiler chickens. Diet supplementation with enzyme led to an increased final body weight and daily weight gain (P < 0.05), without difference according to the bacterial or fungal origin of the xylanase. The Belfeed B1100MP xylanase, which is commercialized in he Walloon region, was selected in order to develop a probiotic-xylanase feed additive. The purpose of the third part was to select a bacterial strain with antagonistic activity against Campylobacter for applying on open-air range and broiler litter. An in vitro screening of 12 lactic acid bacteria was realised using a co-culture assay with a growth medium based on straw and dehydrated poultry excreta, supplemented with different cellulase concentrations. Lactobacillus pentosus and Enterococcus faecium showed inhibitory effect against Campylobacter without enzyme which was intensified by cellulose from 200 ppm. Finally, the effect of dietary supplementation with a L. plantarum strain combined with the Belfeed B1100MP (PE treatment) on growth performance, microflora, and faecal Salmonella Typhimurium concentrations, was studied with experimentally infected broiler chickens. The PE diet allowed to partially overcome the negative effects associated with the infection on growth performance and microflora, and to significantly reduce faecal Salmonella concentration.

La maladie de Newcastle est une maladie virale hautement contagieuse et dévastatrice chez la volaille. Bien que la biosécurité et lhygiène puissent savérer suffisantes pour lutter contre lintroduction de la maladie, la vaccination préventive est considérée comme une précaution supplémentaire et a été rendue obligatoire dans la plupart des pays européens dès les années 90 suite aux épidémies de ND. Cependant, lobservation dépizooties sporadiques témoigne des limites des programmes de prévention actuels. Dans ce contexte, de nombreuses alternatives vaccinales sont étudiées afin de limiter le risque dune infection par le NDV et de réduire la transmission virale, tout en prévenant les signes cliniques et la mortalité. Durant ce travail, la vaccination à un jour à laide dun vaccin atténué a été privilégiée et lamélioration de son efficacité par la co-administration avec ladjuvant chitosan et une primo-vaccination in ovo avec un vaccin recombinant rHVT-ND a été investiguée. Lobjectif de cette thèse consiste à étudier de manière approfondie limmunité induite chez le poulet par la vaccination contre la ND et à établir une corrélation entre les réponses immunitaires mesurées et la protection. Ces expériences ont montré linfluence du tropisme de la souche vaccinale de NDV sur linduction de limmunité à médiation cellulaire et sur le degré de la réponse immune locale en anticorps au niveau des tractus respiratoire et digestif. Cette réponse immune cellulaire spécifique du NDV a pu être renforcée par la co-administration du chitosan avec le vaccin atténué. Linterférence des anticorps maternels sur linduction dune réponse immune spécifique lors dune vaccination à un jour a également été validée. Cet impact négatif a pu être limité par une primo-vaccination in ovo avec un vaccin recombinant rHVT-ND. Enfin, le programme de vaccination combinant une primo-vaccination in ovo avec une vaccination à un jour avec un vaccin atténué co-administré avec le chitosan a permis daméliorer la protection contre les signes cliniques de la maladie mais également de diminuer lexcrétion virale lors dune infection virulente. Cette plus forte protection peut être corrélée avec linduction dune meilleure immunité à médiation cellulaire et une réponse immune locale accrue. Newcastle disease is a highly contagious and devastating condition of poultry. Although good biosecurity and hygiene practices can be sufficient to fight against this disease, the preventive vaccination is thought to be an additional precaution and is rendered compulsory in many European Union countries since the 90 after ND epidemic. Nevertheless, enzootics and epizootics that are sometimes reported point out the limitations of current vaccination regimens. In this context, different approaches have been investigated in order to prevent infection by NDV, reduce the transmission of the virus and eliminate clinical signs and mortality. In this work, we have selected the vaccination at day-old with attenuated ND vaccine and we have attempted to increase its efficacy by the co-administration with chitosan adjuvant and by an in ovo injection of a rHVT-ND vaccine. The aim of this present work was to evaluate the immunity induced by ND vaccination and the establishment of the correlation between the recorded measurement and the protection. These experiments showed the influence of the tropism of the ND vaccine strain on the NDV-specific antibody-mediated immunity in the respiratory and digestive tracts and on the cell-mediated immunity. This NDV-specific cellular immune response was improved by the co-administration of chitosan with the ND attenuated vaccine. It was also observed that the presence of MDA interferes with the establishment of a persisting good protective immunity after a single day-old vaccination. The use of rHVT-ND vaccine applied in ovo as primo-vaccination allowed overcoming this negative interference of MDA. Finally, the innovative rHVT-ND/live ND-chitosan vaccination regimen provided the highest protection against mortality and morbidity as well as the strongest reduction of virus shedding, which could be related to a higher measured cellular immune response and local antibody-mediated immunity.

Résumé: Lauthentification est un concept large dans lequel il sagit de pouvoir contrôler ladéquation entre le produit et les informations indiquées sur létiquette. Les techniques utilisant la spectrométrie dans le proche infrarouge dune part, et celles basées sur la PCR dautre part, permettent daborder lauthentification des produits alimentaires sous des angles totalement différents. Loriginalité de ce travail était de les associer pour résoudre deux problèmes précis : 1. lauthentification des poulets de chair à croissance lente utilisés dans des productions de qualité différenciée soumises à des cahiers des charges contraignants ; 2. la détection des farines animales dans lalimentation pour le bétail. Nos travaux sur les poulets de chair nous ont permis de développer des modèles de discrimination reposant sur les spectres dans le proche infrarouge de la viande de poulet. Ils distinguent, pour plus de 80 % des individus, les poulets issus de souches à croissance lente de ceux issus de souches à croissance rapide. Les résultats dune expérimentation animale ont également démontré que la spectrométrie dans le proche infrarouge était capable de mettre évidence des fraudes au niveau de lalimentation des animaux. Deux marqueurs moléculaires spécifiques du type de souche de poulets ont été mis en évidence et caractérisés. Pour le marqueur moléculaire caractéristique des poulets à croissance rapide, un test rapide utilisable en routine a été développé. Dans le cas de la détection des farines animales dans lalimentation du bétail, une méthode de PCR en temps réel sensible et spécifique a été mise au point participant avec succès à des études inter-laboratoires internationales. Associée dans une stratégie originale à la MPIR (microscopie dans le proche infrarouge), elle permet la détection spécifique de particules de farines de viande et dos. Summary: Authentication is a large concept focussing on the control of the correspondance between the product and the information provided on the label. Techniques based on near infrared spectroscopy on the one hand, and those based on PCR on the other hand, allow to tackle the authentication of food and feed products by different sides. The originality of this work was to associate both techniques to solve two specific problems : 1. authentication of slow growing chickens bred in high quality productions according to restricting specifications ; 2. the detection of meat and bone meals in feedingstuffs. The work on the chicken allowed us to develop discriminant models using the near infrared spectra of chicken meat. These models discriminate the chicken from slow- vs. fast-growing chicken for more than 80 % of the animals. The results of an animal experimentation also showed that near infrared spectroscopy was able to detect feeding frauds. Two molecular markers specific of the type of chicken strains were found and characterised. For the one related to the fast-growing chicken strains, a rapid assay applicable in routine testing was conceived. In the case of the meat and bone meal detection in feedingstuffs, a specific and sensitive real time PCR method was developed. It participated succesfully to international inter-laboratory studies. Its combination with NIRM (near infrared microscopy) through an original strategy allows the specific detection of meat and bone meal particles.