The experiment was carried out to evaluate attributes of pastures and relazed to ingestive behavior, the animal performance and reproduction of beef heifers reared from 15 to 18 months and bred at 18/20 months of age. In observations of ingestive behavior were evaluated heifers on Pearl millet (Pennisetum americanum) and alexandergrass (Urochloa plantaginea). The experimental design was complete randomized following a repeated measure arrangement, with two treatments and two replications. The grazing method was continuous with variable stocking rate in order to maintain the sward height at 40 cm. The leaf, stem and dead material masses, rate of herbage accumulation, leaf/stem relation, leaf and herbage on offer, neutral detergent fiber were similar between Pearl millet and alexandergrass. The ingestive behavior of heifers, measured by grazing, rumination and idle times, bite rate, bite weight, bite by feeding station, feeding stations per minute and rate of displacement was similar when kept in pearl millet or alexandergrass. In performance and reproduction evaluations, in addition to Pearl millet and alexandergrass, it was also evaluated heifers on native pastures invaded by Annoni-2 grass (Eragrostis plana Nees). The differences between the summer annual species (Pearl millet and alexandergrass) and Annoni- 2 grass were tested by contrast analysis. The attributes evaluated in the pasture were different between the annual summer species and Annoni-2 grass. The average daily gain, stocking rate, live weight gain per hectare, body weight, body condition score, weight to height ratio and reproductive tract score of the heifers at 18 months kept on annual summer pastures were superior, compared to the heifers on Annoni-2 grass pasture and resulted in different rates of pregnancy, with values of 75 and 25% respectively. / O experimento foi conduzido com o objetivo de avaliar os atributos das pastagens e relacioná-los com o comportamento ingestivo, com o desempenho animal e com a reprodução de novilhas de corte, na fase de recria dos 15 aos 18 meses de idade e acasaladas aos 18/20 meses. Nas observações de comportamento ingestivo foram avaliadas as novilhas mantidas em milheto (Pennisetum americanum) e papuã (Urochloa plantaginea). O delineamento experimental foi o inteiramente casualizado, com medidas repetidas no tempo, com dois tratamentos e duas repetições de área. O método de pastejo foi com lotação contínua e número variável de animais para manter a altura do dossel em 40 cm. As massas de lâmina foliar, de colmo e de material morto, taxa de acúmulo de forragem, relação folha/colmo, oferta de forragem e de lâmina foliar, teor de fibra em detergente neutro foram semelhantes em milheto e papuã. O comportamento ingestivo das novilhas, medido pelos tempos de pastejo, de ruminação e de ócio, taxa de bocado, peso do bocado, bocados por estação alimentar, estações alimentares por minuto e taxa de deslocamento, foi semelhante quando mantidas em milheto ou papuã. Na avaliação do desempenho animal e da reprodução, além de milheto e papuã, também foram avaliadas novilhas mantidas em campo nativo invadido por capim-annoni-2 (Eragrostis plana Nees). As diferenças entre as espécies anuais de verão (milheto e papuã) e o capim-annoni-2 foram testadas por análise de contraste. Os atributos avaliados na pastagem foram diferentes entre as espécies anuais de verão e capim-annoni-2. O ganho de peso médio diário, a taxa de lotação, o ganho de peso por área, o peso corporal, o escore de condição corporal, a relação peso/altura e o escore de trato reprodutivo aos 18 meses de idade das novilhas mantidas em pastagens com espécies anuais de verão foram superiores aos observados nas novilhas mantidas em capim-annoni-2 e resultaram em diferentes índices de prenhez, com valores de 75 e 25%, respectivamente.

<p>Obesity and nutrition-related non-communicable diseases continue to be major challenges that are increasing in severity worldwide. Science-centered carbohydrate dietary strategies may be a viable approach to help address such challenges. Recent reports from our laboratory indicate that certain carbohydrates with slow digestion profiles have the ability to trigger the gut-brain axis and reduce food intake and to slow gastric emptying and potentially affect appetite. Slow carbohydrate digestion may have other impacts on energy metabolism that have not been explored. In the current investigations, we sought to better understand the delayed gastric emptying profile of pearl millet-based foods as well as to understand how altering carbohydrate digestion rate impacts substrate utilization for energy.</p> <p>In the first study, the physical breakdown of pearl millet couscous particles in a simulated gastric environment (Human Gastric Simulator) was studied compared to wheat couscous matched in particle size, and select physicochemical properties of each type of couscous were characterized. Because we previously showed that pearl millet couscous had a marked delay in gastric emptying compared to white rice, boiled potatoes, and pasta in a human study in Mali, the objective of the first investigation was to test the hypothesis that pearl millet couscous was more resistant to breakdown in the stomach than wheat couscous and would take longer to empty. Our findings indicated that pearl millet couscous instead broke down into smaller, more numerous particles than wheat couscous. However, pearl millet had a slower starch hydrolysis property compared to wheat couscous per unit surface area. Pearl millet also had a smaller amylose chain length (839-963 DP) compared to wheat (1225-1563 DP), which may enable a denser packing of millet starch molecules that hinders hydrolysis. We also visually observed that the pearl millet particles formed a paste while breaking down that could reasonably generate viscosity in the stomach to potentially delay gastric emptying. </p> <p>Based off the findings from simulated gastric digestion, we next conducted a human study (<i>n</i>=14) in the U.S. to test the hypothesis that pearl millet-based foods (couscous – commercial and self-made, thick porridge) would reduce glycemic response, increase satiety, and delay gastric emptying compared to wheat couscous and white rice. We complemented this human study with additional <i>in vitro </i>work using an advanced gastrointestinal digestion system (TIMagc) to determine if the viscosity of pearl millet couscous particles as they were breaking down in the stomach was contributing to a decrease in gastric emptying. Our findings indicated that all the pearl millet-based foods and wheat couscous had lower overall glycemic response than white rice, but only the self-made millet couscous showed higher satiety through subjective appetitive response ratings. Surprisingly, there were no differences in gastric emptying among the foods. Additionally, the half-emptying times for these foods were all ~3 h, which is similar to the comparably low half-emptying times observed for white rice, boiled potatoes, and pasta in the previous Mali study. We now hypothesize that there may be diet-induced changes in gut-brain axis signaling when slowly digestible carbohydrates are consumed repeatedly over time, perhaps through modulating the number or sensitivity of small intestinal L-cells. We also found that millet couscous did not exhibit high viscosity in the TIMagc, suggesting that viscosity was not impacting its rate of gastric emptying. We conclude that at least some pearl millet-based foods possess a slow digestion property that may act to trigger the gut-brain axis or ileal brake to increase feelings of satiety or slow gastric emptying, but the discrepancy between U.S. and Malian populations requires further study. </p> <p>In the final investigation, we examined how altering carbohydrate digestion affected partitioning of carbohydrate versus fat for oxidation as well as the efficiency of switching oxidation between these two substrates (termed “metabolic flexibility”) in mice. Metabolic flexibility has been associated with good health related to decreased adipose tissue in the body and improved insulin sensitivity and may have implications on weight management. Carbohydrate digestion was adjusted by: (1) testing mice that lacked a complete set of enzymes by knocking out maltase-glucoamylase (Mgam; null) for moderating starch digestion versus testing wild-type mice; (2) using diets in these two groups of mice to moderate starch digestion that had different levels of resistant starch (53%, 35%, and 18%), had only raw corn starch or sucrose, or were high in fat; and (3) providing a supplement of fungal amyloglucosidase (AMG) to the mice treatment groups to increase starch digestion. Respiratory exchange ratio (RER) was measured through indirect calorimetry and mathematical modeling was used to characterize the diurnal shifts in RER (sine equation) as well as carbohydrate versus fat oxidation and metabolic flexibility (percent relative cumulative frequency [PRCF] with Weibull and Mixed Weibull Cumulative Distribution functions). Our results suggest that null mice lacking Mgam had somewhat increased metabolic flexibility than wild-type mice despite exhibiting minimal to no effects on carbohydrate oxidation. Intriguingly, the raw corn starch diet increased fat oxidation and generally promoted metabolic flexibility, although it did not increase carbohydrate oxidation relative to the other carbohydrate-predominant diets. Increasing carbohydrate digestion through AMG supplementation increased carbohydrate oxidation, and generally prompted earlier shifts to carbohydrate oxidation than without AMG supplementation. These findings provide a basis for better understanding the metabolic consequences of altering carbohydrate digestion and establish novel tools that can be utilized in future investigations. Overall, we propose that moderating carbohydrate digestion provides the ideal combination of balancing carbohydrate and fat oxidation while promoting metabolic flexibility. </p> <p>In conclusion, a slow digestion property may enable some types of pearl millet to trigger the ileal brake and gut-brain axis feedback systems to decrease glycemic response and increase satiety. Moreover, consuming carbohydrates with slow digestion may optimize substrate utilization for energy by the body. In addition to triggering the ileal brake and gut-brain axis, modulating carbohydrate digestion to more effectively switch between carbohydrate and fat for oxidation may be beneficial for weight management and metabolic disease prevention.</p>

La domestication du mil (Pennisetum glaucum), dans le Sahel, a engendré une large gamme de variétés, très diversifiées pour de nombreuses caractéristiques agronomiques. En particulier, la diversité de la durée du cycle des variétés locales de mil est une composante essentielle des stratégies mises en œuvre par les agriculteurs pour faire face aux fluctuations des précipitations et assurer une certaine stabilité de la production. Au cours des dernières décennies, des évolutions dans les pratiques agricoles ont été observées, en réponse à des changements écologiques et sociaux. Une des conséquences de ces évolutions pourrait être l’existence de flux de gènes entre variétés à cycle court et variétés à cycle long du fait de l’émergence de situations de parapatrie entre ces deux types de variétés, naguère isolées. Par ailleurs, l’existence de recouvrement des périodes des floraisons de ces deux types variétaux a déjà été préalablement observée. Une telle situation amène donc à s’interroger sur la dynamique évolutive passée et actuelle de la diversité de la longueur du cycle du mil dans le Sahel. Dans la première partie de ma thèse, j’ai évalué les possibilités d’occurrence de flux de gènes entre variétés précoces et tardives de mil dans le Sud-ouest du Niger, en utilisant une approche comparative entre situations contrastées pour la distribution spatiale de ces deux types de variétés. J’ai réalisé : 1) une étude des périodes de floraison de deux variétés de mil (précoce (Haïni Kiré) : 75 à 95 jours entre le semis et la maturité et tardive (Somno) : 105 à 125 jours de durée de cycle) dans plusieurs champs paysans, et dans deux villages. 2) une analyse moléculaire à l’aide de 15 marqueurs microsatellites qui a permis l’estimation des niveaux de différenciation génétique entre populations de mils précoces et tardifs échantillonnés dans 4 villages (incluant les deux villages déjà cités) de la même région.Les résultats ont montré la possibilité effective de flux de pollen et l’existence d’introgressions génétiques entre variétés précoces et tardives. Les mécanismes qui pourraient permettre un maintien sur le long terme d’une différenciation phénologique entre les deux types variétaux malgré l’existence de ces flux de gènes, sont discutés.Dans la deuxième partie, j’ai utilisé une approche « gène candidat » combinée à une démarche de génétique des populations, pour tenter d’identifier des gènes qui auraient pu contribuer à la diversité de la durée de cycle chez le mil. Je me suis focalisé sur trois gènes du contrôle de la transition florale PgHd3a, PgDwarf8 et PgPHYC. Leur implication dans la diversité de la durée de cycle chez plusieurs espèces a déjà été montrée. J’ai estimé les niveaux de différenciation génétique entre les mils domestiques et sauvages, précoces et tardifs pour ces trois gènes J'ai aussi cherché à mettre en évidence, au sein de ces gènes, les empreintes éventuelles d’évènements sélectifs passés. Afin de prendre en compte l’histoire démographique des mils dans les tests de neutralité sélective, j’ai utilisé les données de polymorphisme nucléotidiques de 8 séquences témoins dans le cadre d’une approche Bayésienne.Les résultats obtenus suggèrent fortement que PgHd3a et PgDwarf8 ont été ciblés par la sélection durant la domestication. Cependant, les données ne soutiennent pas l’hypothèse d’un rôle potentiel des trois gènes candidats dans la différenciation de la durée de cycle entre les variétés locales précoces et tardives. L’approc / Domestication of pearl millet (Pennisetum glaucum) in the Sahel of Africa has produced a wide range of diversity in cycle duration of landraces. This diversity allows Sahelian farmers to outface the precipitation fluctuation and to ensure regularity in grain production. Due to ecological and social recent changes, modifications of farmer’s practices could be a factor promoting gene flow between the early and late flowering varieties by increasing the opportunity of neighboring and flowering overlap between them. Such a situation raises questions about the past and current evolutionary dynamics of phenological diversity in this crop.In the first part of my thesis I tried to evaluate the possibility of gene flow between pearl millet varieties in South-West Niger, through a comparative approach among contrasting situations pertaining to the spatial distribution of early and late landraces. Therefore I conducted: 1) a field study where we observed flowering periods, for two types of varieties (early type (Haïni Kiré): 75 to 95 days and late type (Somno): 105 to 125 days of cycle length) in several pearl millet fields, and in two villages 2) a molecular study that allows the assessment of the level of genetic differentiation between late and early flowering populations sampled from four villages (including the two where the field study was conducted) of the same region (Dallol Bosso), using microsatellite markers. I was able to demonstrate the occurrence of pollen flow between the two types of landraces and I also showed evidence of genetic introgression between early and semi-late landraces. Potential mechanisms that would allow for the maintenance of the phenological differentiation between these two varieties and despite the gene flow are discussed.In the second part of this work I used a candidate gene and a population genetics approach, to try to identify genes that may have contributed to the cycle length diversity in pearl millet. I focused on three flowering candidate genes, PgHd3a, PgDwarf8 and PgPHYC which have been shown to be involved in the cycle length genetic diversity in several species, in order to estimate the differentiation between wild and domestic pearl millets and between early and late landraces, on the basis of theses candidate genes. I also tried to track for the fingerprint of eventual past selective events within these candidate genes. To be able to distinguish the effects of selection from the effect of demographic events that occurred during the domestication process, I used 8 neutral STS loci and an Approximate Bayesian Computation approach.My results strongly suggest that PgHd3a and PgDwarf8 were likely targeted by selection during domestication. However, a potential role of any of the three candidate genes in the phenological differentiation between early and late landraces was not supported by our data. The Bayesian approach confirmed the idea, suggested by many authors, that the gene flow from the wild to the domestic genetic pool has contributed significantly to the genetic diversity of the domestic pearl millet.