Dans un contexte de fluctuation des prix des intrants et d’une demande croissante en produits à base de lait de chèvre issus de pratiques respectueuses de l’environnement et des animaux, le pâturage peut retrouver une place plus importante dans l’alimentation des chèvres laitières. D’après la synthèse bibliographique, les facteurs de variation de l’ingestion et des performances au pâturage ont été très peu étudiés chez les chèvres laitières en conditions tempérées. L’objectif de la thèse a été de comprendre quelle est l’influence des pratiques de gestion du pâturage (disponibilité en herbe et en temps pour pâturer) sur la régulation de l’ingestion et les performances des chèvres laitières, dans le but d’affiner les recommandations aux éleveurs et d’élaborer les bases d’un modèle de prévision de l’ingestion. D’après les 6 essais réalisés : (1) les chèvres recevant entre 0,6 et 1,0 kg/j de compléments s’adaptent à des restrictions de temps d’accès de 11 à 6 h/j, en augmentant leur vitesse d’ingestion et surtout le pourcentage du temps passé à pâturer jusqu’à 95 % du temps d’accès, (2) les chèvres recevant 0,6 kg de concentrés et un temps d’accès d’au moins 11 h/j peuvent s’adapter à une restriction de quantité d’herbe offerte jusqu’à 2,3-2,6 kg MS/chèvre/j, (3), le poids vif et la production laitière sont des paramètres déterminant de la quantité d’herbe ingérée alors que la parité et le stade de lactation n’ont pas montré d’effet significatif. Ce travail a permis d’établir les premières lois de réponse d’ingestion, de production laitière et d’adaptation comportementale des chèvres laitières à des variations de temps d’accès et de quantité d’herbe offerte au pâturage. / In the context of prices volatility and growing demand for goat's milk products from respectful practices of the environment and animals, grazing can become more important in the diet of dairy goats. According to the literature review, the factors of variation of intake and performance of grazing dairy goats have been poorly studied under temperate conditions. The aim of this thesis was to understand the influence of grazing management practices (availability of pasture and access time to grazing) on the regulation of intake and performance of dairy goats, with the aim of refining recommendations for farmers and to elaborate a model of intake prediction. Based on the six trials conducted: (1) goats receiving between 0.6 and 1.0 kg/day of supplements adapt themselves to access time restrictions from 11 to 6 h/d, by increasing their intake rate and especially the percentage of time spent grazing up to 95% of access time, (2) goats receiving 0.6 kg of concentrates and an access time of at least 11 h/day can adapt to a restriction of pasture allowance up to 2.3-2.6 kg DM/goat/day, (3) live weight and milk production are the main variables affecting intake while parity and stage of lactation had no significant effect. This work provides the first response laws of intake, milk production and behavioural adaptation of grazing dairy goats to variations of access time to pasture and to pasture allowance.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, alÃm dos capÃtulos que envolvem a teoria e definiÃÃes, foi basicamente divido em trÃs estudos: Primeiro (capÃtulo 4), apresentamos uma investigaÃÃo numÃrica do desempenho de um filtro passa-banda totalmente Ãptico composto por um acoplador direcional duplo seguido de duas grades de Bragg simetricamente iguais gravadas nos seus braÃos de saÃda. Esta configuraÃÃo caracteriza um InterferÃmetro de Michelson com caracterÃsticas de um filtro add/drop. As caracterÃsticas de transmissÃo (T), taxa de extinÃÃo (XR) e âcrosstalkâ (XT) foram estudadas a partir da aplicaÃÃo de um sinal CW (onda contÃnua) na entrada do dispositivo. A teoria de modos acoplados e o mÃtodo de Runge Kutta de 4a ordem foram aplicados, respectivamente para resolver as equaÃÃes diferenciais acopladas. Este à o primeiro estudo feito considerando a nÃo linearidade do acoplador e a linearidade das grades de Bragg. O dispositivo apresenta um comportamento altamente nÃo-linear em funÃÃo do defasamento entre as amplitudes dos feixes refletidos e em funÃÃo da potÃncia de entrada. Num segundo momento (capÃtulo 5) apresentamos a propagaÃÃo e chaveamento de pulsos ultracurto (~2ps) usando um interferÃmetro de Michelson de Fibras Ãpticas. Neste estudo o desempenho do interferÃmetro à estudado como uma funÃÃo das caracterÃsticas nÃo lineares do acoplador e das grades de Bragg. Os estudos numÃricos foram feitos a partir das equaÃÃes de modos acoplados resolvidas usando o mÃtodo de Runge-Kutta de 4 ordem. As caracterÃsticas de chaveamento do pulso foram analisadas em funÃÃo da potÃncia de entrada e do defasamento aplicado em uma das grades de Bragg. As caracterÃsticas de transmissÃo (T), coeficiente de ExtinÃÃo (XR), âcrosstalkâ (XT), fator de compressÃo (FC). Utilizamos trÃs valores de potÃncia de entrada: abaixo da potÃncia critica (P0=1W), igual a potÃncia crÃtica (P0=1,73W) e acima da potÃncia crÃtica (P0=1,95W). AtravÃs deste estudo, pode-se verificar que a transmissÃo, taxa de extinÃÃo, âcrosstalkâ e fator de compressÃo dependem da potÃncia da bombeio inserida no dispositivo e da defasagem aplicada. O interferÃmetro de Michelson em fibras implementa componente de grande importÃncia para aplicaÃÃes em redes Ãpticas, como os demultiplexadores add/drop. Este dispositivo tem atraÃdo bastante interesse no campo das telecomunicaÃÃes devido a sua alta capacidade de taxas de transmissÃo. Num terceiro momento foi apresentado um estudo de simulaÃÃo numÃrica do desempenho da codificaÃÃo e decodificaÃÃo de pulsos Ãpticos curtos (ps) em sistemas OCDMA (Optical Code Division Multiple Access â acesso VIII mÃltiplo por divisÃo de cÃdigo no domÃnio Ãptico) baseado em FBG (Fiber Bragg Grating â grade de Bragg em fibra Ãptica) onde os cÃdigos sÃo inseridos atravÃs de saltos discretos na fase Ãptica (Âπ). Para geraÃÃo de pulsos codificados foram utilizados cÃdigos de Gold obtidos analiticamente. Analisamos como a inserÃÃo de cÃdigos adicionais afetam a autocorrelaÃÃo e correlaÃÃo cruzada. O interferÃmetro de Michelson inicialmente estudado no capÃtulo 4 foi utilizado para propagaÃÃo e chaveamento de sinais codificados. Baseados nas caracterÃsticas de TransmissÃo (T) e Taxa de extinÃÃo (XR) fizemos um estudo do dispositivo como multiplexador /demultiplexador add/drop na recuperaÃÃo de pulsos codificados. / This work, in addition the chapters which involves both theory and definitions, was basically divided three studies: First (chapter 4),we present a numerical investigation of the performance of a bandpass filter composed of an all-optical directional coupler, followed by two double bars Bragg recorded symmetrically equal outputs in their arms. This configuration features a Michelson interferometer with characteristics of an add/ drop filter. The transmission characteristics (T), extinction rate (XR) and "crosstalk" (XT) were studied based on the application of a CW signal (continuous wave) into the device. Theory of coupled modes and the Runge Kutta fourth order were applied respectively to solve the coupled differential equations. This is the first study considering the nonlinearity of the coupler and the linearity of Bragg gratings. The device features a highly nonlinear behavior as a function of dephasing between the amplitudes of the reflected beams and depending on the input power. In a second step (section 5), the propagation and switching of ultrashort pulse (~ 2PS) Michelson interferometer using an optical fiber. In this study the performance of the interferometer is studied as a function of the nonlinear characteristics of the coupler and Bragg gratings. The numerical studies were made from the coupled mode equations solved using the Runge-Kutta 4th order. The pulse switching characteristics were analyzed as a function of input power and applied to one dephasing Bragg gratings. The transmission characteristics (T), extinction coefficient (XR), "crosstalk" (XT), the compression factor (CF)and shape of the pulses were analyzed for different values of phase and different input powers. We use three values of input power: below the critical power (1W = P0), equal to the critical power (P0 = 1.73W) and above the critical power (P0 = 1.95W). Through this study, it is found that the transmission rate of extinction, "crosstalk" and compression factor depends on the power of the pump device inserted into the gap and applied The Michelson interferometer fiber implement major component with applications in optical networks, such as demultiplexers add/drop. This device has attracted considerable interest in the field of telecommunications due to its ability of high transmission rates. In the third place was presented a numerical simulation study of the performance of encoding and decoding of short optical pulses (ps) systems OCDMA (Optical Code Division Multiple Access based on FBG (Fiber Bragg Grating ) where codes are inserted through discrete jumps in the optical phase ( π). For generation of coded pulses were used Gold codes obtained analytically. We look at how the inclusion of additional codes affect the autocorrelation and cross correlation.The Michelson interferometer initially studied Chapters 4 was used for propagation and switching of encrypted signals. Based on the characteristics of transmission (T) and extinction rate (XR) did a study of the device as multiplexer/demultiplexer add / drop in the recovery of coded pulses.