MSCAGR (Animal Science) / Department of Animal Science / The overall objective of this study was to investigate the effects of level of dietary concentrate and live yeast (LY) on milk yield, milk composition, rumen fermentation and nitrogen metabolism in lactating dairy cows. Four primiparous Holstein dairy cows in early lactation (average weight 500 ±9 kg and 20 days in milk (DIM)) were used in a 4 x 4 Latin Square design for a period of 44 days. The animals had seven days of adaptation to the treatments and four days for measurements. The treatments were, Low concentrate to forage (C:F) diet (40:60) with no additive, High C:F diet (60:40) with no additive, High C:F diet with LY and Low C:F diet with LY.Cows weremilked at 06h00 and 16h00 daily and milk samples were analysed for fat, protein, lactose milk urea nitrogen (MUN) and somatic cell count (SCC). Proximate analysis of feed samples was done and daily feed intake was recorded. Weight and body condition score were determined at beginning and end of every experimental period. Faecal and urinary nitrogen (N)were determined. In vitro batch fermentation was conducted to determine ruminal fermentation kinetics. Data generated from the feeding trial was analysed for a 4 x 4 Latin square design (LSD) using the PROC MIXED procedure of SAS (2009) and data for the invitro trialwassubjected to ANOVA using PROC GLM (SAS Institute, 2009) for a complete randomized design. Addition of LY affected only dry matter intake (DMI) (P<0.05), which effect was pronounce when cows were fed low (40:60) C:F diet resulting in better feed efficiency(FE). Cows fed high C:F diet consumed more feed, produced more milk with high fat and protein content (P<0.05). Both LY and C:F reduced (P<0.05) N intake as result of low DMI, but reduced (P<0.05) N excretion in manure. Addition of LY decreased ruminal ammonia and increased total VFA’s (P<0.05). The effects on ammonia suggest a better utilisation of diet proteins and probably more incorporation of products of CP degradation into microbial proteins, which support the observed reduced manure N excretion. The opposite was observed with high C:F diet, which increased ammonia and decreased total VFA’s. Propionate and butyrate were increased and decreased, respectively by high C:F diet.Addition of LY reduced SCC and MUN compared to control.The effects of LY were better pronounced on most parameters at low C:F diet. It is therefore recommended that the effects of LY be tested at low C:F on a larger scale of animals over longer periods to observe its effect of the rest of the parameters.

Le but de cette thèse était d'étudier et de mieux comprendre les mécanismes d'interaction entre protéines laitières (caséines micellaires natives NMC et protéines de lactosérum natives WPI) sous forme de poudres dispersées (5% p/v) dans des milieux fortement ionisés par des sels (NaCl, CaCl2). D'une manière générale notre étude a été organisée en trois parties. Premièrement, nous avons étudié l'influence des milieux ioniques (eau distillé, solution de NaCl, solution de CaCl2) sur la réhydratation de protéines laitières. Dans une seconde partie nous avons caractérisé les dispersions en milieux ionisés par les études respectives de la structure secondaire des protéines, de la taille et de la morphologie des particules en cours de dispersion et de l'hydrophobicité des protéines. Dans la troisième et dernière partie nous nous sommes intéressés aux propriétés fonctionnelles des protéines du lactosérum par l'effet combiné de la température (30 - 90°C) et de la concentration en NaCl (0,75 - 3%). La réhydratation des protéines du lait a montré deux comportements distincts en fonction du type de sel d'une part (NaCl, CaCl2) et de la concentration d'autre part (0 - 12%). Dans les dispersions de NMC, avec l'ajout et l'augmentation de la concentration de NaCl on observe (DLS, TEM), une désintégration des micelles de taille 150 nm en petites micelles de 20-30 nm qui sont plus ou moins agrégées. En définitive, les propriétés fonctionnelles des protéines du WPI dépendent en même temps de la concentration en sel et de la température appliquée / The overall objective of this work was to investigate the mechanisms of protein-salt interactions and linkage between milk proteins powders and milk proteins dispersions (5% w/v) mainly NMC and WPI under various ranges of ionic environments (distilled water, NaCl solution and CaCl2 solution. In the first phase, we investigated the influence of the ionic environments on milk proteins powders rehydration profiles. The second phase of this study includes the characterization of milk proteins dispersions in an aqueous ionic environment regarding changes in the protein: secondary structure (ß-sheet, alpha-helix, ß-turns and unordered structures), size, morphological features and surface hydrophobicity by using FTIR, TEM, and DLS with other complimentary techniques. In the last part, the functionality of whey proteins was studied by the combined effect of heat and different ratios of salts. For this purpose, the study was exclusively focalized in an aqueous ionic medium composed of NaCl (0.75-3%) at different temperatures (30-90°C). The results obtained from the first part showed two distinct rehydration behaviors depending on the salts type and concentration. For the NMC dispersions under salt increase, spherical micelles with an average size around 150 nm disintegrated in sub-micelles around 20-30 nm and more or less aggregated were observed by DLS and TEM. WPI dispersions in water were composed of well separated proteins by a spherical shape with two populations around 6 and 70 nm. Salt increase resulted in an aggregation of the proteins and the formation of denser aggregates. Moreover, a combined salt/heat resulted showed a stabilizing effect on the secondary structural elements of both Amide I and III bands and higher denaturation temperatures observed by FTIR and µDSC respectively. A size and morphological investigation showed a transition from spherical/compact protein aggregates to linear ones. Finally, this work demonstrated that whey protein functional properties depend on both salt and how heat treatment is applied

Les petits producteurs laitiers font face à de nombreux défis et risques dans l'établissement de leurs systèmes de production, dans un environnement hautement imprévisible marqué par les incertitudes du climat et du marché, par exemple. Mais les défis et les risques peuvent s'avérer encore plus grands quand ils développent leur système à partir de zéro (ex nihilo), une situation courante dans les zones frontières de l'agriculture et dans le cadre de la réforme agraire au Brésil. Trois concepts principaux sont utilisés pour évaluer la dynamique et la capacité d'adaptation des systèmes en fonction des objectifs à atteindre : la résilience, la flexibilité et la vulnérabilité. Cette thèse présente le concept de vulnérabilité lié à des trajectoires de développement de 24 systèmes de production pilotés par des agriculteurs familiaux d'Unaí, Minas Gerais. Nous proposons une évaluation de la vulnérabilité des systèmes de production de lait, basée sur 10 indicateurs construits sur la base des difficultés identifiées par les agriculteurs familiaux. Les indicateurs sont liés aux trois dimensions des trajectoires : dimension familiale (3 indicateurs), technique (4 indicateurs) et financière (3 indicateurs). Les valeurs d'indicateurs de vulnérabilité entre les différentes années pour le même événement (sècheresse en 2007 et 2011), montrent que la plupart des systèmes de production ont vu leur vulnérabilité baisser au fil du temps. Les indicateurs de vulnérabilité liés à la dimension de la famille sont très stables. Un système peut être vulnérable à la même perturbation dans une période et pas dans l'autre, et vice versa. En perspective de ce travail, nous envisageons de présenter les résultats aux agriculteurs et aux autres acteurs de la filière laitière d'Unaí, pour provoquer une discussion entre eux sur les moyens de "construire" un système de production performant sans augmenter la vulnérabilité du système. / Small dairy farmers face many challenges and risks in developing their production systems, in a highly unpredictable environment marked by uncertainties in climate and market, for example. But the challenges and risks are even greater when they develop their system from scratch (ex nihilo), a common situation in agricultural frontier areas and in the context of land reform in Brazil. Three main concepts are used to assess the dynamics and adaptability of systems, depending on the objectives : resilience , flexibility and vulnerability. This thesis presents the concept of vulnerability related to trajectories of development, as it was applied to assess 24 smallholder farming systems in the region of Unaí (Minas Gerais, Brazil). We propose a framework to evaluate the vulnerability of milk production systems, based on 10 indicators derived from the types of “difficulties” faced along the farm development trajectory as identified by smallholder farmers. These 10 indicators relate to three key dimensions of a trajectory : the family dimension (3 indicators), the technical dimension (4 indicators) and the financial dimension (3 indicators). By comparing values of indicators of vulnerability between different years for the same disturbance (a drought which occurred both in 2007 and 2011), many production systems decreased level of vulnerability over time. There is a great stability of the indicators related to family dimension. The vulnerability of five production systems decreased between 2007 and 2011, but with different amplitudes. A system may be vulnerable to a given disturbance at one moment, not vulnerable at another moment, or vice versa. In the near future, we will present our results to farmers and other actors in the milk production chain in Unaí, with the hope of stimulating discussion among them about the best way to "build" a production system that performs well without increasing the vulnerability of the system.

Der Bericht informiert Milchproduzenten, Berater und Planer über den Energiebedarf konventioneller Melkanlagen sowie Anlagen zur Kühlung von Milch. Enthalten sind sowohl die Ergebnisse von Praxismessungen mit vielen Details als auch Modellkalkulationen. Im Ergebnis werden Empfehlungen für eine Optimierung der Energieeffizienz abgeleitet.