Feeding behaviour is controlled by the integration of both perceived cues from the plant and postingestive signals received by the animal. In general practice, dairy cattle are presented with a variety of feedstuffs throughout each day, in addition to changing feedstuffs over time. In the Australian context, the feeds generally include fodder (usually hay) and pasture whilst grazing, as well as various concentrates. For horses that are stabled for prolonged periods, their diet consists of fodder (again usually hay or chaff) and concentrates, in addition to the pasture consumed whilst allowed access to graze. In such situations, where animals are presented with a range of feedstuffs, some of them novel and for discrete periods of time, it is important that they readily accept the feeds when they are first presented to them. For both lactating dairy cows and performance horses, for example, it is important to avoid periods of low intake, as this can have immediate and sometimes longer-term consequences to animal performance. The daily rate of food intake is the single most important factor affecting animal performance and productivity (Illius et al. 2000) and an animal‟s responses to a feedstuff can be considered the ultimate measure of its quality. The animal‟s first response to the presentation of a new feed, which in this particular study was oaten or lucerne hay, is its level of voluntary intake, which depends in part on palatability. Palatability is an integrative term (Provenza 1995); to provide a quantitative measure of the acceptability of a feedstuff, a „preference value’ can be obtained by describing the preference of one hay relative to an alternate hay also on offer. The Australian fodder industry is increasingly adopting more objective measures of hay quality to improve marketing opportunities, especially in the export industry, and to meet the demands and expectations of local and overseas purchasers of hay. Being able to efficiently and reliably predict the preference value of any particular hay would be beneficial to processors, exporters, users (purchasers) of hay, and possibly plant breeders, to make more informed decisions. This thesis describes a comprehensive analysis of the chemical and physical characteristics of a selected number of oaten and lucerne hays and their relationship to the acceptability or „preference value‟ of the hays for lactating Holstein Friesian cows and Thoroughbred horses. The project aimed to (i) quantify preference values for a large number of oaten hays with dairy cows and horses and a similarly large number of lucerne hays with horses only, and (ii) develop predictive equations for animal preferences based on the chemical and physical properties of the hays and the animal‟s short-term rate of consuming the hays. A total of approximately 8,500 preference tests were conducted with 85 oaten hays offered to lactating Holstein Friesian cows and Thoroughbred horses, and 70 lucerne hays offered to Thoroughbred horses. The hays were selected to cover a range of nutritive values. The intake rate and preferences for all the hays were quantified in a series of tests replicated over time and with different animals. Each „trial‟ hay was offered with four „standard‟ hays (in separate tests). A suite of chemical (nutritive value) traits and physical traits were quantified for the hays. An assessment of the „odour profile‟ was also included in the characterisation of the hays. The nutritive, physical and volatile traits were then related to hay preference values in multiple and simple linear regression models and equations generated to predict hay preference values. A prediction of hay preference made directly from the spectra obtained by near infrared reflectance spectroscopy (NIRS) was also developed. Overall, the average preference value of an oaten hay (i.e., that obtained using the comparisons with all four standard hays) could be predicted from a range of nutritive value traits, typically the contents of acid detergent fibre (ADF), hemicellulose, crude protein (CP) and water soluble carbohydrates (WSC) - with a correlation co-efficient of about 79% with cows and 61% for horses. Acid detergent fibre and CP contents tended to have the biggest influence on preference value for both cows and horses, followed by WSC and hemicellulose content. Examination of lucerne hays offered to horses increased the correlation co-efficient to 74%, with ADF, hemicellulose and CP each having a similar magnitude of effect. This means that these traits, with an appropriate weighting for each, could account for up to about three-quarters of the variation in hay preference values for cows and horses. The in vitro digestibility of dry matter (IVD) of oaten and lucerne hay was nearly as accurate in predicting preference values as using the four nutritive value traits of ADF, hemicellulose, CP and WSC, which was anticipated as digestibility is a function of these chemical traits. Hay physical traits could also be used to predict preference values, although not as accurately as the nutritive value traits or IVD. Of the physical traits, shear energy had the largest effect (co-efficient approximately -1.15 compared to an average of -0.35 for the other traits in the equation). The use of NIRS to directly predict preference values was also encouraging, with the best calibration model yielding a correlation co-efficient of 61 to 81%, depending on the hay (oaten or lucerne) and the animal (cows or horses). Of the total 120 volatile compounds isolated from the oaten hays, six had some relationship with cow preferences and there were also six oaten hay volatiles related to horse preferences. Of the oaten hay volatiles significantly related to preference, four were positively related to cow preference whilst two were negatively related to cow preference. Similarly there were four volatiles positively related to horse preference and two consistently negatively related. Of the six oaten hay volatiles found to influence the preferences of dairy cows and horses, four were common to both species. Of the total of 147 volatile compounds isolated from the lucerne hays, 15 had some relationship with horse preference, with nine positively related to horse preference and six negatively related. The data reported here suggest that a predicted preference value for a hay can be generated using commonly measured quality traits, which would improve a buyer‟s confidence of animals responding favourably when first offered the hay. More specifically, for an average preference value, the most reliable prediction equation was based on nutritive value traits: ADF, hemicellulose, crude protein and water soluble carbohydrates solely. Alternatively a combination of nutritive and physical traits can be used to predict preference: in vitro digestibility, crude protein, water soluble carbohydrates and shear energy. The visible and near infrared spectra obtained by NIRS was also a promising method of prediction, and given the speed and affordability of NIRS, this technology could be further refined and used for routine measurement of predicted hay preference values. The volatile compounds shown to influence preference value of the hay should be identified and further research undertaken to investigate novel approaches to manipulate the preference of hays. Caution should be taken when attempting to use these prediction equations on a single specific hay in a single specific situation. The predictions and relationships investigated in this thesis are based on populations of hays and preferences of a group of animals and therefore some care should be taken when applying them to a particular situation with difference circumstances. Other factors that can influence feed preferences include an animal‟s feeding experiences, basal diet and diet history and various environmental factors unaccounted for here. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1349258 / Thesis (Ph.D.) - University of Adelaide, School of Agriculture, Food and Wine, 2008

Chez la vache Prim’Holstein, un QTL de fertilité a été localisé sur le chromosome 3, et deux haplotypes ont été déterminés : « Fertil+ » et « Fertil- ». Les « Fertil- » ont un plus fort taux d’échec de gestation précoce. Le 1er objectif de cette thèse était de déterminer si un dysfonctionnement des complexes ovocyte-cumulus (COC) pouvait expliquer l’échec précoce de gestation chez les « Fertil- ». L’analyse révèle un retard de maturation, une dérégulation de gènes appartenant aux voies des prostaglandines et des MAPK, et à la famille des Tribbles dans les CC ou l’ovocyte des « Fertil- ». Trois gènes composent la famille des Tribbles chez le bovin: TRIB1, TRIB2 et TRIB3, leur fonction est indéterminée dans le COC. Le 2nd objectif était de caractériser le patron d’expression des Tribbles et leur(s) fonction(s) au sein du COC bovin. Les Tribbles joueraient un rôle dans le métabolisme lipidique et l’inflammation au niveau folliculaire. Le métabolisme lipidique au sein du COC bovin étant peu caractérisé, le 3ème objectif était d’appréhender les profils des gènes du métabolisme des acides gras (AG) dans les CC au cours de la maturation. Ainsi, les CC expriment les gènes lipotytiques et lipogéniques. Enfin, la β-oxydation des AG est une fonction primordiale pour la maturation ovocytaire. / In Prim’Holstein cow, a fertility QTL was localized on chromosome 3 and two haplotypes were determined: « Fertil+ » and « Fertil- ». « Fertil- » have a higher early pregnancy failure rate. The 1st objective of the thesis was to define if complex oocyte-cumulus COC dysfunction could explain the early pregnancy failure in « Fertil- ». Analysis highlighted a maturation delay, a dysregulation of genes involved in prostaglandin and MAPK pathway along with one member of the Tribbles family in « Fertil- » CC or oocyte. In bovine, the Tribbles family is composed of three genes: TRIB1, TRIB2 and TRIB3, their function is unknown within the COC. The 2nd objective was to characterize the Tribbles expression pattern and their function in the bovine COC. The tribbles might play a role in lipid metabolism and in inflammation at the follicular level. Lipid metabolism within bovine COC is poorly understood, thus the third objective was to apprehend fatty acid (FA) genes pattern in CC during maturation. Thus, CC express lipolytic and lipogenic genes. Lastly, FA β oxidation is found to be important for oocyte maturation.

The thesis explores an issue of mastitis in dairy cows, and factors that influence the health of a mammary gland. In span of 2012-2013, 629 quarter samples of milk were collected, the somatic cells count (SCC) was determined and the results related to the condition of teats base, and also to an order and phase of lactation. The results were compared to the pool samples collected in 2008-2013 (SCC, TBC) and the number and development of clinical mastitis was followed (2012-2013). The condition of teats base was estimated as an important factor contributing to the health of a mammary gland. The lowest SCC was identified in the first phase of lactation, and, contrary to that, the highest SCC was identified in the third phase of lactation (active involution). The order of lactation proved to be an important factor influencing SCC in milk. Dairy cows staying in pasture were shown to have less SCC in milk; it can therefore be concluded that grazing has a positive impact on SCC in milk. In the examined period, very low number of clinical mastitis was determined

The aim of this thesi is the evaluation of selected impacts of elimination and longevity of Holstein and Czech spotted dairy cows on the Ing. Bohuslav Vacka´s farm in Vrchotovy Janovice according to the reason of this elimination, the age at the first calving, milk production of the first milk lactation, lifetime milk lactation and the number of milk lactation during the lifetime. I also evaluated functional longevity (from the first calving to retirement) and the longevity of life (from the birth to retirement) of retired dairy cows and the relationship between age at the first calving, milk production of the first lactation and lifetime milk production. In monitoring were included 359 pieces of cows eliminated during five years, from 1 January 2010 to 31 December 2014. From these, 217 pieces of Holstein cows and 142 pieces of Czech spotted cows. Both breeds were stalled in the same barn with the same nutrition. At the monitored group were eliminated altogether 31.22% of dairy cows. Holstein cows were excluded very often from other medical reasons (28.57%) and the Czech spotted cows for fertility disorders (45.77%). Higher milk productivity and higher average number of lactations for the life reached eliminated Holstein cows in comparison with the Czech spotted cows. Longer lifetime longevity reached Holstein cows (63 months) than Czech spotted cows (53.6 months) and among them was found highly significant difference at a significance level of p 0,001. Higher longevity and lifetime milk production in kg of milk reached Holstein cows calved in 25 to 26 months and Czech spotted cows calved within 27 to 28 months. The relationship between age at the first calving and lifetime milk production at Holstein (r = 0.018) and Czech spotted cows (r = 0.0434) proved to be an insignificant dependence and the relationship between milk production at the first lactation and lifetime milk production at Holstein (r = 0.3317) and Czech spotted cows (r = 0.4436) proved to be as a highly significant correlation (p 0.001).

Resumo: O trabalho foi conduzido no Instituto de Zootecnia - Agência Paulista de Tecnologia dos Agronegócios, em Ribeirão Preto. Os tratamentos foram constituídos de quatro dietas experimentais. Dieta I contendo semente de girassol e cana-de-açúcar "in natura"; Dieta II contendo semente de girassol e cana hidrolisada; Dieta III contendo farelo de girassol e cana hidrolisada e Dieta IV contendo óleo de girassol e cana hidrolisada. O período experimental teve duração de 84 dias, composto de três estágios denominados, inicio, meio e fim, de 28 dias cada, sendo os últimos quatro dias utilizados para coleta de dados. Os animais foram distribuídos em um delineamento inteiramente casualizado, composto por quatro tratamentos e seis repetições. A análise estatística dos dados foi realizada utilizando-se o Statistical Analisys System (SAS, 2003). A comparação entre as dietas foi realizada por meio de teste de Tukey. O objetivo deste trabalho constituiu-se em analisar os efeitos da utilização de dietas contendo cana-de-açúcar "in natura" e hidrolisada com Ca(OH)2, associadas a semente, farelo e óleo de girassol na alimentação de vacas mestiças em lactação, sobre os parâmetros metabólicos e fisiológicos, composição do leite e viabilidade econômica. Os tratamentos contendo cana hidrolisada com semente e óleo de girassol apresentaram maiores produções de leite (16,49L e 16,79L). As dietas contendo cana hidrolisada apresentaram maiores teores de Ca. As vacas alimentadas com cana hidrolisada e óleo de girassol apresentaram perfil de gordura no leite de melhor qualidade para consumo. A dieta contendo cana de açúcar hidrolisada e semente de girassol proporcionou maior produção leiteira e melhor receita bruta / Abstract: The sugar cane is a good food in energy, presents high productivity, is available in the dry season and after the maturation keeps its practically constant the nutritional value. However limitations how the low digestibility of fiber can decrease the voluntary dry matter intake. The alkaline treatment in the sugar-cane with Ca(OH)2 can increase the fiber digestibility good efficiency improvements on its digestibility, but the use of lime has raised questions about high levels of calcium in the diet of lactating cows, which could lead to metabolic diseases and losses productivity. This work consisted in analyzing the effects of diets containing sugarcane 'in natura" and hydrolyzed with Ca (OH)2, associated with sunflower meal, sunflower oil, sunflower seed in the diet of lactating cows on the metabolic and physiological parameters, milk composition and economic viability. The present research was carried in Institute de Zootecnia at Ribeirão Preto city to evaluate diets with raw and hydrolyzed sugarcane associated with sunflower (seed, meal and oil).The diets were: I- raw plus seed; II - hydrolyzed plus seed; III - hydrolyzed plus meal and IV - hydrolyzed plus oil. The research was conducted in 84 days, with 3 stages of 28 days included 4 last days to collect data. Twenty four dairy cows were distributed in a randomized design with four treatments and 6 repetitions. Means were compared by Tukey / Orientadora: Jane Maria Bertocco Ezequiel / Coorientadora: Maria Lucia Pereira Lima / Banca: Luiz Francisco Prata / Banca: Mauro dal Secco de Oliveira / Banca: Flávia Fernanda Simili / Banca: Luiz Carlos Roma Junior / Doutor

Orientador: Jorge de Lucas Junior / Banca: Beno Wendling / Banca: João Antônio Galbiatti / Banca: Regina Maria Quintão Lana / Banca: Elias Nascentes Borges / Resumo: A necessidade de ampliação de atitudes que levam o meio rural a buscar a sustentabilidade e a implantação do uso da biodigestão anaeróbia tem sido incentivada por se tratar de um mecanismo de desenvolvimento limpo que alia a importância do tratamento dos resíduos agropecuários (dejetos), geração de energia (biogás) e biofertilizante. Desenvolveu-se um estudo em que se focou a hipótese que a implantação de sistema de tratamento de dejetos, com o uso de biodigestor anaeróbio e o aproveitamento dos seus produtos, o biofertilizante, poderia substituir a adubação mineral nitrogenada de cobertura no cultivo de forrageiras e que essa prática poderia reduzir o custo de adubação e promover ganhos adicionais com a geração de energia elétrica e ganhos ambientais, com a redução de emissão de metano e produção do biogás. Utilizou-se como ferramenta para embasar a hipótese três cultivos de forrageira, um de sorgo e dois de milho. Observou-se que a aplicação de biofertilizante e composto bovino não promoveram aumentos significativos na produtividade das culturas. Paralelamente desenvolveu-se a implantação de um biodigestor de manta de PVC flexível que serviu de parâmetros para a simulação da viabilidade econômica de um sistema de criação de bovino para 100 vacas leiteiras e um sistema de criação de suínos de ciclo completo para 500 matrizes. Conclui-se que projetos que contemplam o princípio da interdisciplinaridade podem auxiliar de maneira mais efetiva na tomada de decisão de implantação de soluções ambientalmente corretas que podem ser também economicamente viáveis. / Abstract: Because of the need for expansion of attitudes that lead to rural areas to seek sustainability. The introduction of the use of anaerobic digestion has been encouraged by the case of a clean development mechanism that combines the importance of processing of agricultural waste (manure), generation of energy (biogas) and biofertilizer. Has developed a study that focused on the hypothesis that the deployment system for the treatment of waste using anaerobic biodigest and use products, the biofertilizer, could replace mineral nitrogen fertilization in coverage the cultivation of fodder and that this practice could reduce the cost of fertilizer and promote additional gains in the generation of electric energy and environmental gains, such as reducing the emission of methane. It was used as a tool for the hypothesis based three of forage crops, one the sorghum and two maize. It was observed that the application of biofertilizer and compost cattle did not promote significant increases in productivity of crops. Developed in parallel to implement a blanket biodigest of flexible PVC that served as parameters for the simulation of the economic viability of a system for creating and veal to 100 dairy cows and a pig breeding cycle of full matrix for 500. It is concluded that projects that include the principle of interdisciplinarity can assist more effectively in decision making for the deployment of environmentally correct solutions that can be economically viable. / Doutor

Resumo: Os objetivos com este estudo foram descrever como as condições de higiene de vacas leiteiras variam ao longo do tempo e de acordo com as estações do ano; avaliar se as vacas são consistentes para sua higiene corporal; estudar as possíveis relações entre o escore de limpeza e o comportamento das vacas, em particular aqueles relacionados ao uso do espaço e à termorregulação e por fim, avaliar se há relação entre o escore de limpeza e a contagem de células somáticas do leite (CCS). Para isso foram utilizados animais de duas propriedades particulares localizadas no estado de São Paulo. Durante nove meses foi realizada uma avaliação mensal da higiene de todas as vacas em lactação, perfazendo um total de 3554 observações para 545 animais. A higiene foi expressa por meio de um escore de limpeza de quatro pontos (muito limpa, limpa, suja e muito suja). Para avaliar a relação entre o escore de limpeza e o comportamento foram avaliadas categorias comportamentais de postura, posicionamento e atividades dos animais para, no mínimo, 46 vacas em lactação, durante três dias consecutivos nos meses de julho e agosto de 2007 (estação seca) e dezembro de 2007 e janeiro de 2008 (estação chuvosa). Para o estudo da relação entre a higiene e a contagem de células somáticas individual das vacas foi avaliado um total de 2218 dados de CCS para 404 vacas. Foi encontrada variação individual na higiene das vacas, sendo que na estação seca os animais apresentaram-se mais limpos que na estação chuvosa. Apesar da variação, aproximadamente metade das vacas é consistente para a sua higiene, permanecendo maior parte do tempo em uma mesma condição - limpa para a maioria. Foi encontrada associação entre a higiene das vacas e o seu comportamento. Para explicar essa associação as categorias comportamentais podem ser caracterizadas em: comportamentos que determinam a transferência... (Resumo completo clicar acesso eletrônico abaixo) / Abstract: The aims of this study were to describe the variation on dairy cow's body hygiene conditions over time and according to the seasons, verify if the cows are consistent for hygiene, to identify the relationship between the cleanliness score and the cow's behavior, particularly those related to land use and thermoregulation and finally, to associate the cow's cleanliness score and their milk somatic cell count (SCC). During nine months the body hygiene was accessed for lactating cows from two Brazilians commercial farms, a total of 3554 observations for 545 animals. The hygiene was expressed as a four points cleanliness score. To evaluate the relationship between the cleanliness score and behavior, behavioral categories of posture, positioning and activities were assessed for at least 46 dairy cows in two months of dry season and two of rainy season. The SCC was accessed for 404 cows, a total of 2218 data. Individual variation was found in the cow's hygiene, and in the dry season the animals maintained cleaner than in the rainy season. Although the variation, approximately half of the cows are consistent for their hygiene - clean for the majority. The body hygiene was associated with the cow's behavior. To explain this association the behavioral categories can be summarized as: behaviors that determine the directly transfer of dirt to the cows' body (to lie down in a mud surface), while others behaviors are indirectly related to the transfer of dirty (lie down in a shaded place). In addition the behaviors as rumination and feeding does not determine the direct transfer of dirt to the body, however, these may be indicators of heat tolerance and the individual social ranking in the group, and differences in these characteristics are related to exposure of animals to certain dirty areas. The cleanliness score have effect on SCC (F = 4.85; df = 3; p < 0,01), and good hygiene condition... (Complete abstract click electronic access below) / Orientador: Mateus José Rodrigues Paranhos da Costa / Coorientador: Marcelo Simão da Rosa / Banca: Luciandra Macedo de Toledo / Banca: Maria Imaculada Fonseca / Mestre

Le lait est produit par les cellules épithéliales mammaires (CEM). La quantité de lait produit est déterminée par le nombre de CEM et leur activité métabolique. Le nombre de CEM dépend de l’équilibre entre la prolifération cellulaire et l’apoptose. Le processus d’exfoliation, défini comme le décrochage des CEM de l’épithélium mammaire et leur évacuation dans le lait, a été proposé comme participant aussi à la régulation du nombre de CEM. Les objectifs de cette thèse étaient d’identifier les mécanismes biologiques impliqués dans la régulation de ce processus et d’étudier son rôle dans la régulation du nombre de CEM et son influence sur la production laitière. Nos résultats montrent qu’une partie des CEM est exfoliée entre deux traites consécutives.Cependant, la majorité des CEM sont exfoliées au moment de la traite suite à la contraction des cellules myoépithéliales et à la perte d’intégrité de l’épithélium induites par la décharge d’ocytocine. Le cortisol, au contraire, participerait à la restauration de l’intégrité de l’épithélium mammaire après la fin de la traite et limiterait l’exfoliation. Nous avons montré que les variations du taux d’exfoliation étaient opposées aux variations de production laitière dans le cas d’une restriction alimentaire et après la fin d’un traitement à l’hormone de croissance mais pas dans le cas d’un changement de fourrage, de l’inhibition de la prolactine et pendant un traitement à l’hormone de croissance. Le processus d’exfoliation des CEM participe donc à la régulation de la production laitière mais pas de façon systématique. / Milk is synthesized by mammary epithelial cells (MEC). Milk yield is determined by the number of MEC in the mammary gland and the metabolic activity of these cells. It is well known that MEC number depends on the balance between cell proliferation and apoptosis. The MEC exfoliation process, defined as the shedding of MEC from the mammary epithelium into milk, is another process that might participate in the regulation of MEC number in the udder and thus in milk yield variations. The aims of this thesis were to identify the mechanisms that regulate the exfoliation process and to study the potential role of this process in regulating the number of MEC and milk yield.Our results showed that some MEC are exfoliated between milkings. Most of the MEC are, however, exfoliated during milking as a consequence of the myoepithelial cell contraction and the disruption of mammary epithelium integrity, both of which are caused by milking-induced oxytocin release. Cortisol may play a role in limiting MEC exfoliation by restoring mammary epithelium integrity after milking. We showed that the exfoliation process participates in regulating milk yield during feed restriction and after a treatment with bovine growth hormone but did not participate in regulating milk yield when forage in the ration was changed, when prolactin secretion was inhibited, or during a treatment with bovine growth hormone. These results suggest that the MEC exfoliation process likely participates in regulating milk yield but not systematically.

O presente estudo teve como objetivo avaliar a associação entre o polimorfismo da &beta;-lactoglobulina e as características físico-químicas (pH, acidez e crioscopia), de composição (gordura, sólidos totais, uréia, proteína bruta, proteína verdadeira, nitrogênio não-protéico e caseína), e de estabilidade do leite. Para tanto, 11 rebanhos leiteiros foram selecionados, 5 da raça Holandesa e 6 da raça Girolanda, dos quais foram coletadas 4 amostras de leite de 164 vacas da raça Holandesa e 74 da raça Girolanda, sendo duas coletas realizadas na estação das secas e 2 na estação das chuvas. Cada amostra foi submetida à análise de composição e de características físico-químicas. Para a identificação do genótipo para &beta;-lactoglobulina, foram coletadas amostras de sangue de cada vaca, as quais foram submetidas à reação de polimerase em cadeia (PCR), determinando-se as freqüências alélicas e genotípicas dos animais. A estabilidade do leite foi avaliada pelo teste de estabilidade ao etanol, nas seguintes concentrações alcoólicas: 70, 76, 80 e 84ºGL. As freqüências genotípicas foram 0,28, 0,30 e 0,41 para os genótipos AA, AB e BB, respectivamente. A freqüência do alelo B foi maior que do alelo A, 0,52 e 0,47, para a raça Holandesa, e 0,58 e 0,41, para a raça Girolanda, respectivamente. Não houve efeito do polimorfismo da &beta;-lactoglobulina (AA, AB e BB), entre os animais das raças, avaliadas sobre as propriedades físico-químicas e a composição do leite. Observou-se efeito de raça (Holandesa e Girolanda, respectivamente) sobre a acidez titulável (16,16 e 17,07°D) e pH (6,78 e 6,75), e de composição do leite quanto as variáveis gordura (3,31 e 3,20%), NUL (16,62 e 14,45mg/dL) e PB (3,13 e 3,04%). Houve efeito da estação (chuvosa e seca, respectivamente) sobre as características físico-químicas de acidez titulável (16,62 e 16,34°D), pH (6,76 e 6,79) e crioscopia (-0,5411 e -0,5376°H), e de composição do leite quanto as variáveis lactose (4,34 e 4,50%), sólidos totais (11,65 e 11,90%), LogCCS (2,44 e 2,34), PB (3,08 e 3,14%), PV (2,84 e 2,91%), caseína (2,01 e 2,13%) e relação caseína:proteína verdadeira (0,70 e 0,72). Verificou-se também efeito da raça e estação do ano sobre a estabilidade do leite, sendo que o leite foi mais instável para raça Girolanda e durante a estação seca, mas não se observou efeito do polimorfismo da &beta;-lactoglobulina sobre esta característica. / The objective of this study was to evaluate the association between beta-lactogobulin polymorphism and physico-chemical characteristics, composition (fat, total solids, urea, crude protein, true protein, non protein nitrogen and casein), and stability of milk. For this aim, 11 dairy herds were selected, six of them composed of crossbred Holstein-Zebu (H-Z) cows and five from Holstein cows. Milk samples were taken four times (twice in dry season and twice in rainy season), from 278 Holstein and 156 crossbred Holstein-Zebu cows. Individual milk samples were analyzed for milk composition and physico-chemical properties. For &beta;-lactoglobulin polymorphism analysis, 10 mL of blood samples were ollected from each cow and then submitted to polymerase chain reaction (PCR). Following &beta;-lactoglobulin protein variants detection, genotype and allele frequencies for the 11 herds were analyzed. Heat stability of milk was determined by the alcohol-induced precipitation test, using the following ethanol concentrations 70, 76, 80 and 84ºGL. The genotype frequencies were 0.28, 0.30 and 0.41 for AA, AB and BB, respectively. Allele B frequency was higher than A, 0.52 and 0.47, for Holstein cows, 0.58 and 0.41, for Holstein-Zebu, respectively. Genetic variants of &beta;-lactoglobulin (AA, AB and BB) had no effect on physico-chemical (acidity, pH and crioscopy), and compositional characteristics (fat, total solids, urea, crude protein, non-protein nitrogen, true protein and casein percentages), either among milk from Holstein cows, or from crossbred Holstein-Zebu. Breed effect for Holstein and H-Z on titrable acidity (16,16 and 17,07°D, respectively), pH (6,78 and 6,75, respectively), fat (3,31e 3,20%, respectively), milk urea nitrogen (16,62 e 14,45mg/dL, respectively) and crude protein (3,13 e 3,04%, respectively) could be observed. Effect of seasonality between rainy and dry seasons was also observed on physico-chemical variables of titrable acidity (16,62 and 16,34°D, respectively), pH (6,76 and 6,79, respectively) and freezing point (-0,5411and -0,5376°H, respectively), and on composition characteristics of lactose (4,34 and 4,50%, respectively), total solids (11,65 and 11,90%, respectively), LogCCS (2,44 and 2,34, respectively), crude protein (3,08 and 3,14%, respectively), true protein (2,84 and 2,91%, respectively), casein content (2,01 and 2,13%, respectively) and casein:true protein ratio (0,70 and 0,72, respectively). Effect of breed and seasonality on milk ethanol stability test was observed. Holstein-Zebu milk was ethanol-unstable on dry season. No effect of &beta;-lactoglobulin on milk stability was observed.

La thèse avait pour objectif de caractériser l’adaptabilité de la glande mammaire, organe support de la fonction de lactation, afin de contribuer à l’étude de la robustesse des vaches laitières et à l’identification de vaches adaptables. L’approche utilisée pour caractériser l’adaptabilité de la glande mammaire consistait à décrire les réponses inter-individuelles de production laitière lors d’une perturbation, puis à identifier des critères phénotypiques et/ou génétiques modulant les caractéristiques adaptatives. Deux modalités d’allongement de l’intervalle entre traites ont été choisies pour perturber le fonctionnement de la glande mammaire : un intervalle de traite unique de 24h (24h-MI) et 3 semaines de monotraite (ODM). Les 2 composantes de l’adaptabilité, à savoir la résistance et la résilience, ont été respectivement estimées par les pertes de lait lors de l’allongement de l’intervalle entre traites et par le taux de récupération au retour à 2 traites par jour,Quatre profils de réponse, définis par leur association des modalités de résistance et de résilience, ont été mis en évidence, dont 3 étaient communs aux 2 perturbations (24h-MI et ODM). Ces profils étaient caractérisés par la compliance de la glande mammaire (c’est-à-dire son aptitude à se distendre) et par son état inflammatoire. Les réponses de production laitière seraient des caractères héritables (h2= 0.32 pour les pertes de lait en kg/j et 0.63 pour la récupération de lait (kg/d), respectivement) ouvrant des perspectives de sélection des vaches sur ces caractères adaptatifs. Les zones du génome influant / This study aimed to enhance knowledge on dairy cows robustness and to enable the identification of adaptable cows through the characterization of the adaptability of the mammary gland, the organ responsible for lactation. The methodology used to characterize the adaptability of the mammary gland consisted in describing inter individual variability in milk yield responses profiles to a perturbation and then identifying phenotypes and/or genotypes that modulated the adaptive characteristics. The mammary gland functioning was challenged by using two different lengthening of milking interval as a perturbation on dairy cows usually milked twice-daily (TDM): a single extended milking interval of 24h (24h-MI) and a 3-wk once-daily milking (ODM). For each of them, the two components of adaptability, resistance and resilience, were estimated by milk yield loss in % when switching cows to 24h-MI or ODM and milk recovery:loss ratio when switching cows back to TDM.Four individual responses profiles, defined by the association of specific resistance and resilience modalities, were found with 3 being common between 24h-MI and ODM. These profiles were characterized by udder compliance (= ability to distend) and mammary inflammation. Milk yield responses were also found to be heritable (h2= 0.32 for milk yield losses and 0.63 for milk yield recovery (kg/d), respectively), so that it could be possible to select animals on these adaptability traits. The genomic regions related to these responses were partly different from regions controlling milk production traits during TDM, so that adapt