Les bactéries lactiques présentent un grand intérêt économique de par leur large utilisation dans l’industrie agroalimentaire. Parmi elles, Streptococcus thermophilus (ST) est d’une importance majeure puisqu’elle est la plus utilisée après Lactococcus lactis, pour la fabrication de produits laitiers fermentés et de fromages. De plus, cette bactérie est le seul streptocoque à bénéficier du statut GRAS (Generally Recognized As Safe). Outre son intérêt en industrie laitière, ST présente des effets bénéfiques sur la santé intestinale de l’Homme. Bien que ces effets soient largement documentés, le statut probiotique de ST reste encore à conforter. C’est pourquoi des études sont actuellement menées afin de sélectionner des souches de ST à fort potentiel probiotique. Parmi les critères importants figurent leur capacité à survivre aux conditions drastiques du tube digestif (TD) et leur capacité à adhérer aux cellules intestinales. Dans cette optique, les objectifs de cette thèse étaient d’étudier, dans un premier temps, la capacité d’adhésion in vitro de la souche ST LMD-9 à différentes lignées cellulaires intestinales d’origine humaine et d’évaluer la survie de cette souche au stress biliaire. Afin de mettre en évidence un rôle potentiel de certaines protéines de surface dans ces deux processus, trois mutants issus de cette souche et inactivés dans les gènes prtS (protéase pariétale), srtA (sortase A) et mucBP (protéine de liaison aux mucines), ont été inclus dans cette étude. Dans un second temps, l’impact de l’adhésion de LMD-9 a été analysé, d’une part sur l’expression de gènes codant certaines mucines dans les cellules eucaryotes, et d’autre part sur l’expression de gènes qui seraient spécifiquement induits durant le processus d’adhésion, ceci en utilisant la technologie R-IVET (Recombinase-based In Vivo Expression Technology). Les résultats obtenus ont permis de montrer que la souche LMD-9 était capable de survivre jusqu’à une concentration de 3 mM en sels biliaires et que les protéines de surface PrtS, SrtA et MucBP seraient impliquées dans la résistance à ce stress. Nos résultats ont également montré que LMD-9 adhérait aux trois différentes lignées cellulaires, suggérant ainsi que la souche pourrait interagir avec les différentes mucines qu’elle peut rencontrer dans le TD. De plus, l’implication de certaines protéines de surface dans l’adhésion de LMD-9 s’est avérée dépendante des caractéristiques de ces lignées, qu’il s’agisse de cellules entérocytaires (Caco-2) ou productrices de mucus (HT29-MTX et HT29-CL.16E). Concernant l’impact de l’adhésion de la souche LMD-9 sur l’expression des gènes MUC2 et MUC5AC, aucun effet sur le taux de transcrits n’a été observé dans nos conditions expérimentales. Par ailleurs, nos résultats ont permis, pour la première fois, d’identifier les gènes spécifiquement induits dans la souche LMD-9 durant l’adhésion aux cellules épithéliales. Nous avons ainsi montré que l’adhésion de la souche LMD-9 ne dépend pas uniquement des protéines de surface, mais d’autres fonctions et voies métaboliques seraient également impliquées. Ce travail de thèse contribue ainsi à apporter de nouvelles connaissances liées (i) au choix du modèle cellulaire dans les études d’adhésion bactérienne in vitro, (ii) à l’aptitude de la souche LMD-9 à survivre au stress biliaire en faisant intervenir certaines protéines de surface et (iii) à la compréhension des mécanismes moléculaires de l’adhésion de LMD-9 aux cellules épithéliales intestinales / Lactic acid bacteria are of great economic interest because of their use in the food industry. Among them, Streptococcus thermophilus (ST) is of major interest since it is the most used after Lactococcus lactis, for the manufacture of fermented dairy products and cheese. In addition, this bacterium is the only streptococcus to benefit from GRAS status (Generally Recognized As Safe). Beside its interest in the dairy industry, ST has beneficial effects on human intestinal health. Although these effects are widely documented, the probiotic status of ST remains to be consolidated. Therefore, studies are currently being conducted in order to select strains of ST with a high probiotic potential. Among criteria that are important to select ST strains include their ability to survive stress the drastic conditions of the digestive tract (DT) and their ability to adhere to intestinal cells. In this context, the aim of this thesis was to investigate firstly the in vitro adhesion capacity of the ST LMD-9 strain to different human intestinal cell lines and to evaluate the survival of this strain to bile salt stress. In order to highlight the potential role of some surface proteins in these two processes, three mutants derived from this strain and inactivated in the genes prtS (parietal protease), srtA (sortase A) and mucBP (Mucin Binding-protein) were also included in this study. Secondly, the impact of LMD-9 adhesion was analyzed, on one hand on the expression of some mucin-encoding genes in eukaryotic cells, and on the other hand on the expression of genes that would be specifically induced during adhesion process using the R-IVET (Recombinase-based In Vivo Expression Technology) approach. The results obtained demonstrated the ability of LMD-9 to survive up to the concentration of 3 mM of bile salts and that the PrtS, SrtA and MucBP surface proteins would be involved in the resistance to this stress. Our results also showed that the LMD-9 strain was capable of adhering to three cell lines used suggesting that this strain could interact with different mucins that may encounter in the DT. Moreover, the involvement of some surface proteins in the adhesion of LMD-9 has been found to be dependent on the surface characteristics of these cell lines, whether they are enterocytic (Caco-2) or mucus-secreting cells (HT29-MTX and HT29-CL.16E). Regarding the impact of LMD-9 adhesion on MUC2 and MUC5AC gene expression, no effect has been observed on the transcript level under our experimental conditions. Furthermore, for the first time, our results allowed us to identify genes specifically induced in the LMD-9 strain during adhesion process to epithelial cells. We have thus shown that the LMD-9 adhesion does not depend solely on surface proteins, but other functions and metabolic pathways are also involved. This thesis work contributes thus to new knowledge related to (i) the choice of the cellular model in in vitro bacterial adhesion studies, (ii) the ability of LMD-9 to survive bile salt stress by involving some surface proteins and (iii) understanding the molecular mechanisms of LMD-9 adhesion to epithelial cells

Orientador: Maria Cristina Thomaz / Coorientador: Caio Abércio da Silva / Banca: Pedro Henrique Watanabe / Banca: Fábio Enrique Lemos Budiño / Banca: Márcia Rita Fernandes Machado / Banca: Pamela Rodrigues Reina Moreira / Resumo: Foram conduzidos três experimentos para avaliar diferentes fontes de fibras purificadas e seus efeitos em dietas, com níveis proteicos reduzidos, sobre o desempenho e a saúde intestinal de leitões recém-desmamados. No experimento I foram caracterizadas quatro fontes de fibras purificadas, quanto à capacidade de retenção de água, volume de intumescimento, microestrutura e viscosidade. No experimento II foram avaliados o desempenho, a incidência de diarreia e o tempo de trânsito gastrointestinal de 84 leitões desmamados aos 26 dias de idade. No experimento III foram avaliados o pH, o peso relativo de órgãos do trato gastrointestinal, as concentrações de ácidos graxos de cadeia curta e ácido lático, a morfologia e a microbiologia da mucosa intestinal, os escores de lesão, as células em apoptose e mitose, e a imunidade intestinal de 42 leitões desmamados aos 26 dias de idade. Nos experimentos II e III, os animais foram distribuídos em um delineamento em blocos completos casualizados, com seis tratamentos: DC: dieta controle sem redução proteica; DR: DC com redução de quatro pontos percentuais da proteína bruta; DF1, DF2, DF3 e DF4: DR com adição de 2,0% de lignocelulose, celulose, pectina e goma guar, respectivamente. A inclusão de goma guar à dieta resultou em piores (P<0,05) ganho diário de peso e conversão alimentar, assim como no maior (P<0,05) tempo de trânsito gastrointestinal comparado à inclusão de celulose, que apresentou o menor. O peso final dos leitões f... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Three trials were conducted to evaluate different purified fibers sources and their effects in diets with reduced protein level on performance and intestinal health of weanling pigs. In trial I were characterized four purified fiber sources as to the water retention capacity, swelling volume, microstructure and viscosity. Performance, incidence of diarrhea and gastrointestinal transit of time of 84 piglets weaned at 26 days of age were evaluated in trial II. In trial III were evaluated pH, the relative organs weight of the gastrointestinal tract, concentrations of fatty acid short chain and lactic acid, the morphology and microbiology of the intestinal mucosa, the lesion scores, the apoptosis and mitotic cells and the intestinal immunity of 42 piglets weaned 26 days old. In both experiments, the animals were distributed in a randomized complete block design, with six treatments: CD: control diet without protein reduction; RD: CD with a reduction of four percent of crude protein; DF1, DF2, DF3 and DF4: RD with addition of 2.0% of lignocellulose, cellulose, pectin and guar gum, respectively. The inclusion of guar gum in the diet resulted in worse (P<0.05) daily gain and feed conversion, as well as the largest (P<0.05) gastrointestinal transit time compared to the inclusion of cellulose, which had the lowest. The final weight of the piglets was lower (P<0.05) with the addition of guar gum compared to the control diet, pectin and lignocellulose. The animals fed cellulose have the lowest (P<0.05) Lactobacillus count and the best (P<0.05) ratio of villus height and crypt depth, not differing from lignocellulose, but with the other evaluated diets. In the duodenum the number of cells in apoptosis was lower (P<0.05) in the animals fed diet with cellulose, the number of cells in mitosis was bigger (P<0.05) with control diet and pectin and the lesion scores ... (Complete abstract click electronic access below) / Doutor

O bem-estar animal pode influenciar o sistema produtivo na avicultura de postura. Sendo assim, o sistema free-range ou \"ao ar livre\" sem o uso de antibióticos surge como uma alternativa aos sistemas confinados. Espera-se que esse sistema torne-se cada vez mais difundido em atenção à demanda do mercado consumidor e bem-estar animal. Neste estudo, são abordados à influência da ambiência nas características qualitativas da cama aviária e ninhos, qualidade do ar, padrões fisiológicos e comportamentais, e avaliação da microbiota intestinal de galinhas poedeiras criadas no sistema free-range sem o uso de antibióticos. O estudo foi conduzido em um galpão comercial de galinhas poedeiras da linhagem Lohmann Brown. O período experimental correspondeu da 18ª a 24ª semanas de idade, para as avaliações relacionadas à ambiência, parâmetros fisiológicos e comportamentais. Para a estimativa da densidade bacteriana intestinal, as aves foram avaliadas durante o período de produção dos ovos, correspondendo à idade de pré-pico de postura (13ª semana), pico de postura (24ª semana) e pós-pico de postura (63ª semana). Água e ração foram fornecidas ad libitum. Constatou-se que as condições climáticas foram favoráveis, ou seja, as aves permanceram dentro da zona de termoneutralidade e na faixa de conforto térmico ideal. Resultados referentes à amônia volatilizada foram satisfatórios, assim como a umidade da cama e ninhos. Não houve incidência de pododermatite e as condições de empenamento das aves permaneceram íntegras nas regiões avaliadas. As avaliações comportamentais das aves demonstrou que as mesmas estavam em totais condições de bem-estar animal, ademais os níveis de corticosterona foram significativamente inferiores. Em relação ao estudo da microbiota intestinal das aves, as análises revelaram diferentes padrões de densidade dos simbiontes em relação às regiões estudas. A população das bactérias benéficas foi significativamente maior em comparação as bactérias patogênicas. Os simbiontes intestinais estudados demonstraram crescimento diferencial ao longo do período estudo. Diante do exposto, podemos reportar que o sistema free-range sem o uso de antibióticos apresentou qualidade de vida às aves poedeiras no que tange o bem-estar animal. / Animal welfare quality may affect egg laying livestock. Thus, the antibiotics-free free-range rearing system (AFFRS) came to light as an alternative to conventional production systems. Furthermore, it is expected AFFRS become more and more widespread as a response to consumer demand and animal welfare rules. In here, we aimed to evaluate the influence of the ambiance on the avian litter and nests, air quality, bird physiology and behavioral patterns, and their intestinal microbiota as well. The study was carried out using Lohmann Brown laying hens breed of the 18th to the 24th weeks-old kept in a commercial shed, and the environmental, physiological and behavioral parameters were evaluated. Additionally, gut microbiota was estimated by using hens of three different egg production cycles. The first cycle was represented by grower hens with 13th weeks of age as their reproductive organs were developing (i.e. early cycle), followed by 24th weeks-old grower hens (high egg production cycle), and 63th weeks-old grower cycle hens (late egg-laying cycle). Water and feed were supplied ad libitum. Data demonstrated birds were in optimal thermal comfort and the volatilized ammonia concentration remained at very low rates, as well as the bed and nest moisture levels. There was no incidence of pododermatitis and the conditions of feathering of the birds remained intact. Animal welfare conditions were optimal as demonstrated through behavioral data and corticosterone levels. Furthermore, gut microbiota densities were different between target symbiont-groups of the same gut region and among different gut segments investigated. Beneficial bacteria densities were significantly higher than pathogenic bacteria and gut symbionts showed differential growth curve throughout the studied period. Thus, our results demonstrated that the AFFRS met the laying hen\'s welfare quality rules and can be considered a good alternative rearing system to the egg production industry.

Submitted by Franciele Moreira (francielemoreyra@gmail.com) on 2018-02-09T13:52:40Z No. of bitstreams: 2 Dissertação - Hyara Paula Fleuri Xavier - 2017.pdf: 1558991 bytes, checksum: 03535b693efa8cdc053f47c33646cd59 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Liliane Ferreira (ljuvencia30@gmail.com) on 2018-02-09T14:41:58Z (GMT) No. of bitstreams: 2 Dissertação - Hyara Paula Fleuri Xavier - 2017.pdf: 1558991 bytes, checksum: 03535b693efa8cdc053f47c33646cd59 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-02-09T14:41:58Z (GMT). No. of bitstreams: 2 Dissertação - Hyara Paula Fleuri Xavier - 2017.pdf: 1558991 bytes, checksum: 03535b693efa8cdc053f47c33646cd59 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-08-10 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / The objective of this essay was to evaluate the use of guava extract processing as an antioxidant additive on the diet of Japanese quail matrices about the parameters on the matrices fertile performance on posture phase and the newborn quail parameters in the quality and internal health resulted from the eggs of these matrices. Three experiments were done in the School of Veterinary and Animal Science in the Federal University of Goiás (EVZ/UFG) and in all three of them, it was adopted the completely randomized design (CRD). In the first experiment, 384 Japanese quail matrices were used, 288 being females and 96 males, distributed in 4 groups, following the level of guava extract inclusion on the diet of the matrices, with a recurrence of 6 times each group, in a total of 12 females and 4 males in each recurrence. The levels of guava extract inclusion were 0,0%, 0,3%, 0,6% and 0,9%. In the second experiment, it were collected 162 eggs from each group during three days and at the end of the third day they were put in the incubator, in a total of 648 eggs. In the third experiment, 432 eggs were collected and put in the incubator in a factorial arrangement that considered two periods of preincubation storage – 216 eggs with nine days and 216 eggs with 3 days – and the four levels of guava extract inclusion on the diet of the matrices. The performance data results were submitted to the variance analysis and the quality data of the eggs were submitted to the regression analysis. The newborn quails quality parameters were submitted to the regression analysis. The hatch window were submitted to the Tukey’s test, the embryo diagnosis and the score percentage were assessed by Fisher’s exact test, the villus height analysis and intestinal crypt depth were submitted to the variance analysis. It was adopted in all the analysis 5% of probability. The use of guava extract has not influenced neither the birds’ performance nor the physicochemical quality of the eggs. In the second experiment, there was no statistical difference to the percentage of total hatch and the percentage of hatch/fertile, hatch window and the quality score of the newborn quails among the four levels of extract inclusion. The birth dispersal in the group with 0,0% of guava extract inclusion was lower than the other dispersions. 0,3% level of inclusion, the guava extract promoted improvements in the newborn quails intestinal health. In the third experiment, the guava extract inclusion was able to standardize the birth dispersal in both storage periods and promote the maintenance of the newborn quails resulted from the eggs stored for nine days. This study concludes that the use of the guava extract has not affected the matrices’ fertile performance and helped to standardize the hatch window as well as promoting intestinal health of the newborn quails. / Objetivou-se avaliar o uso do extrato de resíduo de goiaba como um antioxidante zootécnico nas dietas de matrizes de codornas Japonesas sobre os parâmetros de desempenho produtivo das matrizes em fase de postura, qualidade de ovos, incubação e parâmetros de qualidade e desenvolvimento intestinal das codornas neonatas oriundas de ovos dessas matrizes. Foram realizados três experimentos no aviário experimental da Escola de Veterinária e Zootecnia da Universidade Federal de Goiás (EVZ/UFG) e em todos adotou-se delineamento inteiramente casualizado (DIC). No experimento 1, foram utilizadas 384 matrizes de codornas Japonesas, sendo 288 fêmeas e 96 machos, distribuídos em 4 tratamento, de acordo com o nível de inclusão do extrato de goiaba na dieta das matrizes, com 6 repetições cada tratamento, num total de 12 fêmeas e 4 machos em cada repetição. Os níveis de inclusão do extrato de goiaba foram: 0,0%, 0,3%, 0,6% e 0,9%. No experimento 2, 162 ovos por tratamento foram coletados durante três dias e incubados ao final do terceiro dia, num total de 648 ovos. No experimento 3, 432 ovos foram coletados e incubados em esquema fatorial que considerava dois períodos de armazenamento pré incubação – 216 ovos com nove dias e 216 ovos com três dias – e os quatros níveis de inclusão do extrato de goiaba na dieta das matrizes. Os resultados dos dados de desempenho foram submetidos à análise de variância e os dados de qualidade de ovos foram submetidos à análise de regressão. Os parâmetros de qualidade das codornas neonatas foram submetidos à análise de regressão. As janelas de eclosão foram submetidas ao teste de Tukey, as análises de embriodiagnóstico e percentagem de escore foram avaliadas pelo teste exato de Fisher, as análises de altura de vilosidades e profundidade de criptas intestinais foram submetidas à análise de variância. Em todas as análises adotou-se 5% de probabilidade. A utilização do extrato de goiaba não influenciou o desempenho das aves nem a qualidade físico-química dos ovos. No experimento 2 não houve diferença estatística para percentagem de eclosão total e percentagem de eclosão/férteis, janela de eclosão e escore de qualidade das codornas neonatas entre os quatro níveis de inclusão do extrato. A dispersão dos nascimentos no tratamento com 0,0% de inclusão de extrato de goiaba foi menor do que as demais dispersões. Ao nível 0,3% de inclusão, o extrato de goiaba promoveu melhorias no desenvolvimento intestinal das codornas neonatas. No experimento 3, a inclusão do extrato de goiaba foi capaz de padronizar a dispersão dos nascimentos em ambos os períodos de armazenamento e promover a manutenção do desenvolvimento intestinal das codornas neonatas oriundas de ovos armazenados por nove dias. Conclui-se que o uso do extrato de goiaba não afetou o desempenho produtivo das matrizes e auxiliou na padronização das janelas de eclosão bem como no desenvolvimento intestinal das codornas neonatas.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / ABSTRACT: The laying phase requires intense activity of the poultry organism, sothe equilibrium in the metabolism is necessary to a efficient production. Thus, this work aimed to evaluate the expression of genes superoxide dismutase (SOD), Glutathione peroxidase 7 (GPX7), acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), apolipoprotein A-I (APOA-I),And apolipoprotein B (APOB) in the liver; Tumor necrosis factor alpha (TNFα), glutathione peroxidase 7 (GPX7), catalase (CAT) and superoxide dismutase (SOD) in intestine; estrogen receptor 1 (ESR1) and estrogen receptor 2 (ESR2) in ovary; the histomorphometry of intestinal traits, productive performance, organ morphometry, antioxidant activity, oxidative stress markers, and serum parameters of lipid metabolism of Japanese laying quails fed with diets with or without cinnamon powder added to the diet. It was used 144 quail (Coturnix japonica) with initial age of 18 weeks, distributed in two treatments (basal diet without supplementation of cinnamon (SC) and basal diet plus 9g / kg of powdered cinnamon (CC)). At the end of the proposed experimental period, six animals from each treatment were euthanized by cervical dislocation, blood was collected and the organs weighed. Liver, intestinal and ovary tissues were collected for RNA extraction, enzymatic analysis and histological analysis. The cDNA was amplified using primers specific for the genes analyzed by qRT-PCR. Increased ovary weight was observed in the CC treatment birds; they also presented higher villus height, higher crypt depth, as well as better feed conversion by egg mass, higher triglyceride, uric acid and VLDLcontent.Regarding the amount of thiobarbituric acid reactive substances (TBARS) and the activity of the enzyme catalase (CAT), higher values were observed in the liver of SC treatment birds. The CC treatment birds presented higher expression of FAS, ACC, APOA-I, SOD, GPX7 and ESR2 mRNA. The supplementation of cinnamon powder in the laying quail diet makes egg production more efficient by promoting balance in the body through antioxidant activity and modulation of the expression of genes related to antioxidant defense systems and lipid metabolism. / RESUMO: A fase de postura exige intensa atividade do organismo das aves, e para que a produção seja eficiente é necessário que haja equilíbrio no metabolismo como um todo. Assim, este trabalho teve como objetivo avaliar a expressão dos genes: superóxido dismutase (SOD), glutationa peroxidase 7 (GPX7), acetil-CoAcarboxilase (ACC), ácido graxo sintase (FAS), apolipoproteína A-I (APOA-I), e apolipoproteína B (APOB), no fígado; fator de necrose tumoral alpha (TNFα), glutationa peroxidase 7 (GPX7), catalase (CAT) e superóxido dismutase (SOD) no intestino; além do receptor do estrógeno 1 (ESR1) e receptor do estrógeno 2 (ESR2) no ovário; assim como a histomorfometria de seguimentos do intestino, o desempenho produtivo, a morfometria dos órgãos, atividade antioxidante, marcadores do estresse oxidativo, parâmetros séricos do metabolismo lipídico de codornas japônicas em fase de postura alimentadas com dietas com e sem adição de canela em pó a ração. Foram utilizadas 144 codornas japônicas (Coturnix japonica) com idade inicial de 18 semanas, distribuídas em dois tratamentos (dieta basal sem suplementação de canela (SC) e dieta basal mais suplementação de 9g/kg de canela em pó (CC)). Ao final do período experimental proposto, seis animais de cada tratamento foram eutanaseados por deslocamento cervical, o sangue foi coletado e os órgãos pesados. Tecidos do fígado, intestino e ovário foram coletados paraextração de RNA, análises enzimáticas e analises histológicas. O cDNA foi amplificado usando primers específicos para os genes analisados pela qRT-PCR. Maior peso de ovário foi observado nas aves do tratamento CC, estas também apresentaram maior altura de vilo, maior profundidade de cripta, bem como melhor conversão alimentar por massa de ovo, maior conteúdo de triglicerídeos, ácido úrico e VLDL. Com relação à quantidade de substâncias reativas ao ácido tiobarbitúrico (TBARS) e a atividade da enzima catalase (CAT) maiores valores foram observados no fígado das aves do tratamento SC. As aves do tratamento CC apresentaram maior expressão de mRNA FAS, ACC, APOA-I, SOD, GPX7e ESR2. A suplementação de canela em pó na dieta de codornas em fase de postura torna a produção de ovos mais eficiente por promover equilíbrio no organismo através da atividade antioxidante e modulação da expressão de genes relacionados aos sistemas de defesa antioxidante e metabolismo lipídico. / São Cristóvão, SE

Il y a actuellement une pression mondiale pour revoir les pratiques d'utilisation des antimicrobiens (UAM) en production animale afin de limiter la propagation de bactéries résistantes aux antibiotiques. Conséquemment, les Producteurs de Poulet du Canada examinent la possibilité de réduire leur UAM en supprimant les antibiotiques médicalement importants en médecine humaine (AIM) des programmes préventifs avec la mise en place de leur stratégie de réduction de l’UAM. Cependant, les informations sont rares sur les conséquences de telles approches dans un contexte canadien. L'objectif de cette thèse était d'étudier les impacts sur les performances zootechniques, le contrôle des maladies intestinales et le microbiote cécal de deux stratégies de réduction de l'UAM dans des troupeaux commerciaux de poulets de chair par rapport à une UAM conventionnelle. Sur sept fermes commerciales de poulets de chair, un poulailler a été attribué aux traitements de réduction des antibiotiques pour six troupeaux consécutifs, tandis qu'un poulailler similaire sur le même site a été alloué à l'UAM conventionnelle (CONV) pour six troupeaux consécutifs (n = 84). Les stratégies de réduction des antibiotiques consistaient en l'utilisation continue d'ionophores dans l'alimentation sans (TX1) ou avec de l'acide butyrique (TX2). Aucune différence statistique (p > 0.05) n’a été notée entre TX1, TX2 et CONV sur les performances zootechniques et la santé intestinale. Les comptes d’oocystes d’Eimeria spp. étaient significativement (p < 0.05) inférieurs entre 22 et 34 jours d'âge dans les troupeaux CONV comparé aux TX1 et TX2. Le type de programme antibiotique a eu un impact relativement mineur (valeur R = 0.039), mais statistiquement significatif (p = 0.002), sur le microbiote cécal, tandis que les facteurs environnementaux ont montré les corrélations significatives (p = 0.001) les plus fortes avec le microbiote. Parmi les composantes du microbiote cécal associées à la croissance, le gain quotidien moyen (GMQ) était significativement associé à la Richesse bactérienne (p < 0.05). L’abondance relative de la famille bactérienne Lachnospiraceae fut la mesure la plus fortement corrélée à un GMQ augmenté, tandis que l’abondance relative de nombreuses familles bactériennes, incluant les Porphyromonadaceae, les Planococcaceae et les Veillonellaceae, fut corrélée à un faible GMQ. Ces taxons défavorables formaient un vaste réseau de corrélations positives entre elles, et négativement corrélées aux Lachnospiraceae. En conclusion, ces travaux ont contribué à améliorer la résilience de l'industrie avicole en fournissant des stratégies alternatives aux AIM pour prévenir les maladies intestinales. Des connaissances importantes sur le microbiote cécal des poulets de chair furent générées et pourront considérablement influencer les directions futures de la manipulation du microbiote pour favoriser la croissance. Par exemple, un paradigme important a été remis en question en illustrant que les additifs médicamenteux dans l'alimentation n’influencent que marginalement le microbiote cécal et que ce sont plutôt des facteurs environnementaux qui sont fortement impliqués dans la formation des communautés bactériennes cécales. La clé pour développer un microbiote cécal idéal chez les poulets de chair pourrait résider dans la capacité d'influencer ces facteurs, plus particulièrement l'exposition précoce à des communautés bactériennes bénéfiques et le contrôle de la flore résidente spécifique à la ferme. / There is a global pressure to review current antimicrobial use (AMU) practices in animal production and limit large-scale propagation of antibiotic resistant microorganisms. Consequently, the Chicken Farmers of Canada are examining the possibility to responsibly reduce AMU by discontinuing medically important antibiotics (MIAs) for humans from disease prevention programs of broiler chicken flocks through the implementation of their Antimicrobial Use Reduction Strategy. However, information is sparse on the consequences of such approaches in a Canadian commercial poultry production context. The general objective of this thesis was to investigate the impacts of two strategies reducing AMU in commercial broiler chicken flocks on zootechnical performance, control of intestinal diseases and the cecal microbiota compared to conventional AMU. On seven commercial broiler chicken farms, a house was allocated to the antibiotic reduction treatments for six consecutive flocks, while a similar house on the same premises was assigned to the conventional AMU (CONV) for six consecutive flocks (n = 84). The antibiotic reduction strategies consisted of continuous in-feed ionophores without (TX1) or with butyric acid (TX2). There were no statistical differences (p > 0.05) between TX1, TX2 and CONV for zootechnical performance and intestinal health. Predicted Eimeria spp. oocysts were significantly lower (p < 0.05) between 22 to 34 days of age in CONV flocks compared to TX1 and TX2. The type of antibiotic program had a relatively minor impact (R-value = 0.039), but statistically significant (p = 0.002), on the cecal microbiota composition, while environmental factors such as the farm and flock cycle showed the strongest statistically significant (p = 0.001) correlations with the microbiota composition (R-values of 0.239 and 0.374, respectively). Amongst the cecal microbiota components associated with weight gain, the average daily gain (ADG) was significantly associated with bacterial Richness (p < 0.05). The relative abundance of the bacterial family Lachnospiraceae was the most important measure correlated with ADG, while the relative abundance of numerous bacterial families, including Porphyromonadaceae, Planococcaceae and Veillonellaceae, were correlated with decreased growth rate. These unfavourable taxa formed a large network of positive correlations, indicating potential co-occurring synergies between these undesirable taxa. This network was also negatively correlated to Lachnospiraceae. In conclusion, the findings in this work contributed to improve the sustainability of the modern poultry industry by providing feasible alternatives to the practice of using MIAs for the prevention of intestinal diseases in broiler chickens. This project also generated important knowledge on the cecal microbiota of broiler chickens that could considerably influence future directions of microbiota manipulation in a perspective of improving zootechnical performance. For instance, an important paradigm was challenged by the indication that in-feed antibiotics and prebiotics may only influence marginally the microbiota during grow-out. Rather, this work suggests environmental factors are strongly involved in shaping the bacterial communities residing in the ceca of broiler chickens. Hence, the key to successfully develop an ideal cecal microbiota in broiler chickens may reside in the ability to influence such factors, more specifically the early exposure to beneficial bacterial communities and the control of farm-specific resident flora.