A series of four experiments were conducted to evaluate whether a preconditioning period, in which adult leghorn cockerels are allowed 3 weeks to adapt to diets containing relatively high levels of guar meal (GM) resulted in changes in digestive tract morphology and ecology. It was expected that these changes would result in increased utilization of GM as birds became acclimated to consuming it at high levels. In the 1st experiment, 28 birds were fed diets containing 0, 6, 12, or 24% GM. Consuming the 24% GM diet resulted in decreased body weight, increased small intestine, liver, and pancreas weight, increased ceca and villus length, and increased severity of injury to the intestinal mucosa (P < 0.05). In the 2nd experiment, 28 cockerels were subjected to a partial cross-over experiment. Preconditioning to the 24% GM diet resulted in decreased TMEn of GM, decreased body weight, and decreased absorptive capacity of the GI tract as evidenced by increased energy lost via the excreta (P < 0.05). The 3rd experiment evaluated how differences in endogenous energy losses (EEL) from 30 cockerels affected the TMEn content of GM in birds consuming 0, 6, or 12% GM. Decreased EEL was observed in birds conditioned to 6 and 12% GM relative to the control group (P < 0.05). Further, decreased TMEn of GM was observed in birds consuming 6% GM relative to those consuming the control diet (P < 0.05). In the 4th experiment, changes in cecal microbiota were evaluated in 24 cockerels consuming 0, 6, or 12% dietary GM using denaturing gradient gel electrophoresis of amplified bacterial DNA sequences. Cecal microbiota of birds consuming 12% GM was considerably different from the control group (similarity coefficient = 84%) with an apparent decrease in the complexity of microbial communities. Results of these studies show that consuming 12% dietary GM results in changes in the cecal microbial community which may be responsible for modest increases in the TMEn of GM when compared to 6% dietary GM, which consistently resulted in decreased TMEn values of GM. Further, determining the TMEn value of GM appears to be highly dependent upon factors such as preconditioning diet and timeframe and innate physiological "thresholds" which seem to initiate or limit the maximum physiological response to preconditioning that the bird is capable of.

Dans un contexte de limitation de l'utilisation des antibiotiques, de nouvelles stratégies doivent être mises en place pour préserver la santé des animaux, en particulier lors du sevrage. En cuniculture, les stratégies de limitation de l'ingestion permettent de réduire les troubles digestifs en post sevrage et améliorent l'efficacité alimentaire, mais induisent inévitablement un retard de croissance et une baisse du rendement à l'abattage. Ce travail de thèse avait pour objectif d'une part d'optimiser les performances de croissance et de rendement à l'abattage des animaux soumis à une restriction alimentaire via une modulation de la quantité et de la qualité énergétique des aliments et d'autre part d'expliciter les mécanismes physiologiques sous-jacents aux effets bénéfiques d'une ingestion restreinte sur la santé et l'efficacité alimentaire. Nous avons démontré que dans le cadre d'une stratégie de restriction alimentaire un aliment riche en énergie digestible permet d'optimiser la croissance (+2%), le rendement à l'abattage (+0,6 points) et l'efficacité alimentaire (+11%), via notamment une amélioration de l'efficacité digestive, sans pénaliser les paramètres sanitaires, mais ne permet de rattraper que partiellement le retard de croissance induit par la restriction alimentaire (-3% de poids à l'abattage par rapport aux animaux nourris à volonté). Un aliment riche en amidon était favorable à la croissance de ces animaux et en particulier au rendement à l'abattage et n'avait pas d'effet délétère sur les paramètres sanitaires. La restriction alimentaire et la concentration énergétique alimentaire dans une moindre mesure, modulaient la réponse immunitaire via une réduction de la réponse humorale digestive (IgA intestinaux) et systémique (IgA et IgG circulants) sans modification de la réponse inflammatoire. L'activité du microbiote caecal était quant à elle modulée par la masse d'aliment ingérée alors que le profil de la communauté bactérienne caecale, sa diversité et sa richesse ne semblaient pas modifiés par la restriction alimentaire. Toutefois l'abondance relative de certaines familles (Eubacteriaceae, Peptococcaceae et Christensenellaceae) et genres montraient des variations spécifiques à la restriction ou à la concentration énergétique de l'aliment. L'ensemble de ces résultats indiquent que les relations entre les mesures physiologiques et les effets bénéfiques de la restriction alimentaire sur la santé digestive restent complexes et suggèrent l'implication d'autres paramètres métaboliques non évalués. Des hypothèses complémentaires de travail doivent ainsi être envisagées Toutefois nos travaux établissent l'intérêt économique de la restriction alimentaire, quel que soit le contexte sanitaire, et celui de l'utilisation d'aliments à haute valeur énergétique sur les performances zootechniques. Notre étude ouvre dès lors des perspectives de recherches complémentaires d'optimisation des stratégies alimentaires via une modulation de la durée de restriction alimentaire et de la qualité énergétique des aliments. / With the reduction in antibiotic use new strategies are required in order to preserve animal health, particularly around weaning. In rabbit breading feed restriction strategies allow for the reduction of post-weaning digestive disorders and improve feed efficiency, but are inevitably responsible for a reduced growth and carcass yield at slaughter. This work aimed to optimize the growth performances and slaughter yield of restricted fed rabbits through a modulation of the dietary energy concentration and quality. The second objective of this work was to explain the physiological mechanisms underlying the beneficial effects of feed restriction upon health and feed efficiency. We demonstrated that, under a restriction strategy, a diet rich in digestible energy increased growth (+2%), slaughter yield (+0.6 points) and feed efficiency (+11%), through an improved digestive efficiency, without penalizing the sanitary parameters. The reduced growth induced by feed restriction was however only partially compensated for (-3% in final weight compared to the ad libitum fed animals). A diet rich in starch induced a higher growth and slaughter yield and did not penalize the sanitary parameters under a restriction strategy. Feed restriction and, to a lesser extent, the dietary energy concentration, modulated the immune response through a reduced humoral response at the digestive (fecal IgA) and systemic (plasmatic IgA and IgG) levels without modifying the inflammatory response. The cecal microbial activity was modulated by the amount of feed ingested while the cecal bacterial community profile, diversity and richness were not affected by the feed intake level. However, the relative abundance of certain families (Eubacteriaceae, Peptococcaceae and Christensenellaceae) and generas demonstrated specific variations according to the feed intake level and the dietary energy concentration. These results indicate that the relationship between the physiological measurements and the beneficial effects of feed restriction upon health remain complex and suggest the implication of other metabolic parameters that weren't measured. Complementary work hypothesis must therefore be considered. This work however enabled us to establish the economic advantage of feed restriction strategies regardless of the sanitary status and demonstrated the beneficial effects of a high energy diet on growth parameters. Our study opens the door to new complementary research projects regarding the optimization of the feeding strategies through for instance the modulation of the restriction length and the dietary energy quality.