La fertilité des vaches laitières s’est beaucoup dégradée au cours des dernières décennies, tant à l’échelle nationale qu’internationale. L’objectif poursuivi est d’apporter un éclairage épidémiologique sur les relations dynamiques entre la conception (réussite à l’insémination artificielle ; IA), les mammites subcliniques et les déséquilibres métabolico-nutritionnels que sont la cétose subclinique et les déséquilibres azotés de la ration. Un premier chapitre bibliographique dresse l’état de l’art des liens entre performances de reproduction et (i) mammites, (ii) cétose subclinique et (iii) excès de protéines dégradables, en identifiant clairement les interactions et associations croisées entre ces différents composants, et en quantifiant autant que possible ces liens. Les trois parties suivantes mobilisent des données exhaustives du contrôle laitier français sur la période 2008-2012, qui ont été confrontées aux données d’IA. La variable d’intérêt retenue est la conception après IA, soit pour la première IA (IA1) ou pour toutes les IA. Les variations des concentrations de cellules somatiques (CCS) autour de l’IA ont été utilisées pour décrire la dynamique des mammites subcliniques autour de l’IA, selon 4 classes (Bas-Bas, Bas-Haut, Haut-Bas et Haut-Haut) et pour différents seuils de CCS. Le statut de cétose subclinique a été évalué grâce aux taux butyreux et protéique du lait. Les concentrations d’urée du lait sont utilisées pour caractériser les déséquilibres azotés. Le second chapitre propose une description succincte des résultats de production et de reproduction des troupeaux bovins laitiers français sur la période d’étude. Le troisième chapitre focalise sur l’interaction entre les CCS et la cétose subclinique dans un modèle de régression de Poisson expliquant la conception. Les chances de conception à l’IA1 sont réduites de 14% (Risque relatif = 0,86 [IC 95%=0,85–0,87]) pour les groupes Bas-Haut et Haut-Haut, comparé au groupe Bas-Bas, et de 3 à 17 %, selon les définitions retenues, lors de cétose subclinique comparé à son absence. Les résultats identifient et quantifient clairement l’interaction entre la cétose subclinique et les mammites subcliniques dans leur association avec la conception : la baisse de la conception est jusqu’à 2 fois supérieure lors de la présence simultanée d’une augmentation des CCS et d’une cétose subclinique par rapport à la situation où il y a seulement augmentation des CCS. Le quatrième chapitre, mobilisant des méthodes proches de celles du chapitre précédent, montre que la baisse de la concentration d’urée dans le lait autour de l’IA (en dessous de 150 mg/kg, 2,6 mmol/L) est associée à une baisse de la conception de 5 à 9% (Risque relatif = 0.91 (IC95%=0,87-0,96)]) par rapport à des concentrations d’urée du lait qui restent stables (250 - 450 mg/kg ou 4,3-7,7 mmol/L). Ceci révèle l’importance de la stabilité du métabolisme azoté autour de la conception, y compris pour des variations d’urée du lait ou du sang à la baisse, alors que seule la hausse de la concentration d’urée était identifiée comme un facteur de risque de dégradation des résultats de reproduction jusqu’alors. La dernière partie permet de mettre en perspective ces éléments originaux. Une des principales limites de ces travaux est la définition imprécise de la cétose subclinique réalisée à partir des taux du lait ; les résultats actuels bénéficieraient d’une actualisation avec un indicateur plus précis de ce trouble. Ces résultats soutiennent qu’une inflammation locale peut affecter la réponse de l’ensemble de l’organisme et altérer les fonctions d'autres organes dans les semaines qui suivent son apparition. Ils illustrent la complexité et les interactions entre les différents troubles chez un même animal. Par ailleurs, maintenir des concentrations basses de l’urée est légèrement pénalisant pour la conception, et ne garantit pas de meilleurs résultats de reproduction. / Reproductive performances of dairy cows are recognized as a key parameter for the profitability of dairy farms, but they are getting worse continuously in many countries during the last decades. Infectious and nutritional disorders are possible contributors to these changes. Mammary infection, nitrogen imbalance and metabolic disorders have been reported to be negatively associated with conception, but their interactions and dynamics are not fully understood. The objective of the present work is to better describe the relationship between fertility, udder health, subclinical ketosis (SCK) and nitrogen imbalance accounting for the temporal variations of these events and their interactions. The first section reviews the link between reproductive performances and (i) mastitis, (ii) metabolic disorders and (iii) nitrogen imbalance in dairy cows in order to clarify the complex interaction among these events. The three other sections are based on exhaustive data from the national French dairy milk improvement system and data on the artificial inseminations (AI) from 2008 to 2012. Fertility was explained as conception at the first (AI1) or at all AI. The udder health status was evaluated through the somatic cells counts (SCC). Several proxies based on the milk fat and protein contents were proposed to define SCK. Milk urea concentration was used to investigate the exposure to nitrogen imbalance. The second section aims to describe the actual situation of milk production and reproduction in French dairy herds. The third section focuses on the interaction between SCC and SCK and their association with conception. On average, the risk of conception at AI1 was 14% lower when the SCC increased or remained high within 40 days before and after AI (Relative risk [and 95% CI] = 0.86 [0.85–0.87]), compared to low SCC before and after AI. The reduction in conception rate associated with SCK (fat and protein contents changes) varied from 3% to 17% depending on the SCK proxy used. Including the interaction term SCC*SCK clearly showed that the association of increased SCC around AI with conception was modified by the presence of SCK. A cow that already has SCK and experiences an increase in SCC around or after AI exhibits up to 2 times further decrease in conception, compared with a cow with a high SCC and no SCK. The fourth section, using similar methods as the previous one, shows that low milk urea concentrations after AI are negatively associated with conception. Cows with a low urea (< 150 mg/kg, 2.6 mM) after AI have a reduced conception (Relative risk RR [and 95% CI] = 0.96 [0.94–0.99]) compared to cows with intermediate urea (250-450 mg/kg, 4.3 - 7.7 mM) after AI. Furthermore, the risk of conception was 5 to 9% lower (relative risk [and 95% CI] = 0.91 [0.87–0.96]) when urea concentrations decrease from intermediate before to low after AI, compared with cows with constant intermediate urea values. This work revealed that a decrease in urea from intermediate (before AI) to low (after AI) is a risk factor for conception failure in addition to the previously known risk factor that is nitrogen excess. The final section aims to highlight the perspectives of these results. The definition of SCK used in this work was identified as the main limitation and the present results would benefit from an update with a better indicator of this disorder. The present work supports that a local inflammation may affect the entire body response and alters the functions of other organs like those of the reproductive tract. Furthermore, maintaining low urea concentrations does not provide any particular advantage and might be negatively associated with conception.

No description available.

Améliorer la santé des vaches laitières en élevage agrobiologiques (AB) est bien souvent nécessaire, pour ces élevages ne répondant pas toujours aux principes de l’AB et aux attentes des consommateurs d’avoir un niveau de santé et bien-être animal élevé. Cette thèse explore des voies d’amélioration du conseil sanitaire en vue d'améliorer la santé animale dans ces élevages. Les résultats de nos travaux montrent que les vétérinaires ont le plus souvent un rôle de thérapeute dans les élevages laitiers AB. L'obtention d'un rôle de conseiller a été entravée par des spécificités liées à l’AB, telles que les différences entre éleveurs et vétérinaires dans les objectifs de gestion de la santé des animaux et les pratiques sanitaires. Une étude d'intervention a été effectuée pour tester un dispositif de conseil dans des élevages AB en France et en Suède, basé sur l’utilisation d’outils de surveillance et prévention de maladies de production. Le dispositif a été réalisé en utilisant une approche participative, impliquant l’éleveur et le conseiller ; la flexibilité de l’outil a permis de produire un protocole de surveillance adaptée à chaque élevage. Bien qu’aucun effet sur la santé du troupeau n’a été prouvé, le dispositif a été perçu pour contribuer à la santé du troupeau par ses utilisateurs. Il a rempli la plupart de ses fonctions prévues de surveillance et de prévention des maladies et a stimulé le dialogue entre éleveurs et conseillers. Des outils qui stimulent le dialogue et qui sont adaptables à chaque élevage sont une voie à suivre pour le développement du conseil en santé animale. / Improving herd health on organic dairy farms is often needed, since organic dairy farms do not consistently meet the organic principles and consumers’ expectations of high animal health and welfare. This thesis explores ways to improve the pertinence of herd health advisory services in order to improve animal health on organic dairy farms. The results of our studies show that veterinarians mostoften have a role of therapist on organic dairy farms. Obtaining a more advisory role was hampered due to specificities of the organic sector, such as differences between farmers and veterinarians in animal health management objectives and practices. An intervention study was performed testing a Herd Health and Production Management (HHPM) program on organic dairy farms in France and Sweden, based on herd health monitoring and disease prevention activities. The program was built using a participatory approach, making farmer and advisor work together ; the adaptability of the program allowed to design farm specific herd health monitoring tools. Although no effecton herd health measured, the program was perceived to contribute to herd health by its users. The program fulfilled most of its intended functions in herd healthmonitoring and disease prevention and stimulated dialogue between farmers and their advisors. We consider that dialogue promoting and tools adaptable to farm specific situations are a possible way forward for the development of advisory services in animal health.

This experimental work investigated the development and testing of a controlled release system for methionine. Methionine is one of the limiting amino acids for the milk production in dairy cows. The quantities of methionine which reach the small intestine are affected by the bacteria in the rumen which utilize methionine. A controlled release system which will offer a protective barrier for methionine may ensure that the methionine reaches the small intestine in sufficient quantities. The work involved the development of a coating around methionine crystals, which would act as a barrier, protecting it from the rumen conditions. Zein and kafirin proteins from maize and sorghum, respectively, were used as the principal coating components for the controlled release system. Two different approaches were used in the development of the controlled release system. First, the zein and kafirin proteins were tested for their ability to act as barriers for the controlled release of methionine, and second, zein and kafirin microparticles were used as the controlled release agents. Relatively successful, laboratory-scale methods were developed for coating the methionine with the proteins and the microparticles. Protein coatings were made by addition of methionine crystals to acid-dissolved proteins which led to the formation of a protein/methionine matrix. For coating the methionine with microparticles, glacial acetic acid was used to fuse microparticles around the methionine crystals. Dissolution assays were performed to test the release of methionine from the coatings under simulated rumen conditions. Both the zein and kafirin and microparticle coatings exhibited a barrier effect for methionine. The barrier effects of these coatings were influenced by several factors. Increasing the proportion of the coating agents led to improved barrier properties. However, this only occurred until a certain proportion of coating agent was present (50%), after which the barrier properties no longer increased. Heat treatment of the coatings also increased the barrier properties of the coatings. This may be due to the formation of disulphide cross-links being formed during the application of heat. When a simple extrusion method was used to form the coatings, the barrier properties also improved in comparison to those coatings which were not formed using extrusion. When producing the microparticles, it was found that only the laboratory extracted kafirin preparation with 85% (db) protein formed microparticles. It was hypothesized that microparticle formation might be related to the purity of the protein preparations. Scanning electron microscopy of the coatings after the dissolution tests and pepsin digestion revealed pores on the surface of the coating. These were probably where the methionine leached from the coating into the dissolution medium. The protein coatings did act as partial barriers, extending the release of methionine. From the release curves of methionine from the coatings, it could be seen that a sustained release of methionine occurred over a period of time, rather than a controlled release of methionine at a certain time. The aim of the application was thus only partially achieved as a complete protective barrier for methionine was not obtained from the protein coatings. No significant difference between the barrier properties of the coatings prepared from the proteins themselves and the microparticles were found. However, when based on equal protein purity the kafirin protein coatings showed the most effective barrier properties. Further research regarding kafirin coatings as a controlled release agent is recommended based on the results of the above named calculation. This research would entail investigating various coating technologies and methods. / Dissertation (MSc)--University of Pretoria, 2011. / Food Science / unrestricted

Rumen acidosis is a metabolic disorder of ruminants, characterized by a severe drop in rumen pH. This is due to an accumulation of acids, especially lactic acid in the rumen. Lactic acid is one of the strongest acids with a major effect on rumen pH. A low and / or fluctuating rumen pH can have a severe impact on the productivity and health of dairy cattle, especially during the early lactation period. Rumen acidosis can, for example, occur during the rapid change from a low concentrate to a high concentrate diet. Megasphaera elsdenii (Me) is a lactate-utilizing micro-organism that converts the lactic acid that is produced from the fermentation of starch in the rumen, to propionic acid. Based on the ability of Me to convert lactic acid to propionic acid, a study was conducted to determine the effect of dosing live sources of Me on the level of rumen acidosis, general health and productivity. Sixty high-producing multiparous dairy cows were used in a randomized complete block design experiment. Cows were blocked according to milk production during the previous lactation and, thereafter, randomly allocated, within each block, to one of the following treatments: <ol> <li> 60% concentrate TMR;</li> <li> 60% concentrate TMR with Me dosing;</li> <li> 70% concentrate TMR;</li> <li> 70% concentrate TMR with Me dosing.</li></ol> The experimental period was 60 days and cows were dosed on day 2, 10 and 20 post-partum. Cows were housed in a semi-intensive housing unit equipped with Calan gates for determining individual feed intake. Daily milk production and dry matter intake were measured, as well as body mass and body condition score. Milk was analyzed for fat, protein, lactose and MUN; rumen fluid for pH, volatile fatty acids and lactic acid; faecal samples for pH and starch and feed refusal samples for nutrient components. In addition the health statuses of the cows were also monitored. In general the results did not show a clear advantage of dosing Me, regardless of the level of concentrate. Dry matter intake, milk production, milk composition, feed efficiency, body mass and body condition score were not affected by treatment (P > 0.05). Contrary to expectation, treatment did not affect rumen pH, rumen lactic acid or volatile fatty acid concentrations (P > 0.05). Faecal pH, however, was higher and the starch content lower in cows dosed with Me (P < 0.05) suggesting a positive effect on rumen fermentation and more efficient total tract starch fermentation. Furthermore only two cows were culled from the dosed group, compare to eleven from the control group, suggesting a positive influence of Me on the general health of stress, early lactation cows. Further research is needed to better quantify the potential role of Me in preventing SARA. / Dissertation (MSc(Agric))--University of Pretoria, 2008. / Animal and Wildlife Sciences / unrestricted

Orientador: José Luiz Moraes Vasconcelos / Resumo: Dois experimentos foram conduzidos para avaliar o efeito de diferentes fontes de energia e da suplementação com cromo nas variáveis relacionadas a resistência à insulina, produção de leite e índices reprodutivos de vacas leiteiras lactentes consumindo excesso de energia que foram distribuídas em um arranjo fatorial 2 × 2. No primeiro estudo, vacas foram designadas a receber: 1) concentrado a base de milho moído (CRN; n = 13) ou polpa cítrica (PLP; n = 13) e 2) suplementação (n = 14) ou não (n = 12) de 10 mg/vaca/dia de propionato de cromo. No segundo estudo vacas receberam: 1) concentrado a base de milho moído (CRN; n = 20) ou com inclusão de 8% (matéria seca) de gordura de palma protegida (CSPO; n = 20), e suplementação (n = 20) ou não (n = 20) de 10 mg/dia de propionato de cromo. Para a condução de ambos os estudos, foram utilizados animais não gestantes, Holandeses × Gir, lactantes (dias de leite inicial = 80 ± 3), alimentados com silagem de milho oferecida de maneira ad libitum e concentrado visando atender 160% dos requerimentos energéticos de mantença. Amostras de leite e sangue foram colhidas semanalmente e produção de leite foi mensurada diariamente. Para o primeiro estudo, escore de condição corporal (ECC) e peso corporal (PC) foram avaliados semanalmente ao longo do estudo (D0 ao 182), enquanto que no segundo estudo ECC e PC foram avaliados no primeiro e no último dia (d0 e d203, respectivamente) do estudo. Ingestão de matéria seca foi avaliada apenas no segundo est... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

O desenvolvimento de tecnologias alternativas para facilitar a mensuração da produção de calor e de metano em animais é necessário e deve trazer efeitos positivos para a indústria de produção animal. O objetivo do presente trabalho foi correlacionar a temperatura em pontos anatômicos mensurados através de termografia infravermelha com a produção de calor e a emissão de metano em vacas Holandês e mestiças Holandês x Gir. Seis vacas mestiças Holandês e Gir e quatro vacas Holandês no período médio da lactação, primíparas, foram avaliadas quanto à produção de calor e à emissão de metano diárias, por calorimetria indireta, em câmaras respirométricas. A termografia foi feita nas regiões do ânus, da vulva, da costela (no lado direito), do flanco direito, do flanco esquerdo, da pata dianteira direita, do lábio superior, do masseter e do olho. As imagens termográficas foram tomadas nesses nove pontos anatômicos anteriormente citados, a cada hora, por oito horas após a alimentação da manhã, durante cinco dias. Durante todo o experimento, as vacas receberam a mesma dieta ad libitum e a produção de leite e o consumo foram registrados diariamente O estudo compreendeu 40 dias, incluindo os dias de adaptação dos animais às câmaras respirométricas. A produção diária de metano foi associada com a termografia infravermelha do olho na hora 6 após a alimentação em vacas mestiças Holandês x Gir (r=0,85, p<0,05) e com a termografia infravermelha do olho feita na hora 5 em vacas Holandês (r=0,88, p<0,05). Além disso, a produção de calor foi correlacionada com a termografia infravermelha da pata dianteira direita uma hora após a alimentação em vacas Girolando F1 (r=0.85, p<0.05) e com a termografia infravermelha do olho cinco horas após a alimentação em vacas Holandês (r=0,90, p<0,05). Esses resultados foram posteriormente confirmados usando análise de regressão. As correlações das imagens termográficas com a produção de calor e emissão de metano foram similares entre as vacas Holandês e as vacas Girolando F1. A termografia infravermelha é efetiva na avaliação da produção de calor e da emissão de metano de vacas em lactação Holandês e Girolando F1, embora realizadas em pontos anatômicos diferentes. / The development of alternative technologies that more easily assess heat and methane production of livestock animals are needed and would have positive effects on the livestock industry. The aim of this study was to correlate skin temperature assessed through infrared thermography with heat and methane production in lactating Holstein and Holstein x Gir crossbreed cows. Six Holstein and Gir crossbred and four Holstein cows, all primiparous, at midlactation were used to evaluate daily heat production and methane emissions through indirect calorimetry in respiratory chambers. Thermographic images were taken at nine different body locations every hour during eight hours after feeding for five days. Thermographic images were taken at the following regions: anus, vulva, ribs (on the right side), left flank, right flank, right front foot, upper lip, masseter and eye. During the whole trial cows received the same diet ad libitum, milk yield and feed intake were daily recorded. Data collection lasted 40 days, including adaptation of the animals to the respiratory chambers Daily methane emission was correlated with infrared thermography taken at the eye six hours after feeding in Holstein x Gir crossbred cows (r=0.85, p<0.05) and with infrared thermography taken at the eye five hours after feeding in Holstein cows (r=0.88, p<0.05). Also, heat production was correlated with infrared thermography taken at the right front foot one hour after feeding in Holstein x Gir crossbred cows (r=0.85, p<0.05) and with infrared thermography taken at the eye five hours after feeding in Holstein cows (r=0.90, p<0.05). These results were further confirmed using regression analysis. Correlations between infrared thermography and heat production or methane emissions are similar for Holstein and Holstein x Gir crossbred. Infrared thermography is effective in assess heat production and methane emission in Holstein and Holstein x Gir crossbred lactation cows albeit taken in different anatomical points.

Ruminant feed supplements are price sensitive and are effected by the continuous fluctuation of other raw material feed prices. Therefore, improving the efficiency of production and reducing cost of supplement concentrates for dairy cows are becoming increasingly important both for the smallholder and commercial dairy farmer. This can be overcome by replacing expensive energy and protein feeds with cheaper by-products. During periods of high maize prices, replacing maize with lower cost high fibre by-products becomes an economically viable option. Palm kernel expeller (PKE) fits the profile of a low cost, high fibre by-product. The aim of this study was to determine the effect of different inclusion levels of PKE in dairy concentrates for Jersey cows on milk production, milk composition, body weight (BW) and body condition score (BCS) change, rumen parameters and in situ ruminal kikuyu/ryegrass pasture degradability of dry matter (DMd) and neutral detergent fibre (NDFd) as well as NDFd rate (NDF kd). The study was conducted at the Outeniqua Research Farm situated near George in the Western Cape and cows grazed high quality kikuyu/ryegrass pasture during spring. Forty eight multiparous high producing Jersey cows were blocked according to 4% fat corrected milk (FCM), days in milk (DIM) and lactation number and randomly allocated to three treatments (control, low PKE, and high PKE). The PKE inclusion level in the control, low PKE, and high PKE treatment concentrates was 0, 20, and 40%, respectively. The PKE replaced part of the maize and protein sources in the concentrate. Milk yield was recorded daily and milk composition was determined in two week intervals over a 60 d period, after a 21 d adaptation period. Additionally, eight lactating rumen-fistulated cows were randomly allocated to the control and high PKE treatment in a two period crossover design. Ruminal pH, volatile fatty acids (VFA’s), ruminal ammonia-nitrogen (NH3-N), and in situ ruminal kikuyu/ryegrass pasture DMd, NDFd and NDF kd were measured. Cows received 6 kg (as is) concentrate per day divided over two milking periods and strip grazed kikuyu/ryegrass pasture as one group. Milk yield and milk fat content did not differ (P > 0.05) between treatments and were 21.3, 21.3 and 20.7 kg/cow/d and 4.63, 4.65, and 4.66% for cows receiving the control, low PKE and high PKE treatments, respectively. Milk protein, milk urea nitrogen (MUN), BW and BCS did not differ (P > 0.05) between treatments. Total VFA’s, average ruminal pH, ruminal NH3-N, and in situ ruminal kikuyu/ryegrass pasture DMd and NDFd as well as NDF kd did not differ (P > 0.05) between treatments. The acetic to propionic acid ratio was, however, higher (P < 0.05) for cows supplemented with the high PKE treatment. It can be concluded that partial replacement of maize with 20 or 40% PKE in a lactating dairy cow concentrate did not affect milk yield, milk fat content, milk protein content, somatic cell count (SCC), BW, or BCS. Rumen fermentation was unaffected and a healthy rumen environment was sustained. The replacement of higher cost maize and soybean oilcake by a lower cost PKE decreased feed cost. It is however not recommended to include PKE at 40% in the concentrate due to the increased time spent by cows in the milking parlour and the low palatability of PKE, which could lead to the tendency of increased concentrate refusals. It can be extrapolated from the data obtained from this study that milk production will be sustained when PKE is fed to cows on pasture at 2.4 kg/cow/day. / Dissertation (MSc Agric)--University of Pretoria, 2013. / gm2014 / Animal and Wildlife Sciences / unrestricted

Le méthane, puissant gaz à effet de serre (GES), est produit dans le rumen des bovins par la fermentation microbienne anaérobie des aliments. Cette production est également responsable d’une perte d’énergie pour l’animal représentant 6 % à 8 % de l’apport alimentaire. Pour ces raisons, plusieurs travaux de recherches sont entrepris pour réduire ces émissions, en jouant sur la composition des aliments ou sur l’utilisation d’additifs alimentaires. Actuellement, la mesure des émissions de méthane se fait par différentes techniques, qui présentent des inconvénients, notamment le coût ou encore la difficulté d’application à grande échelle sur le terrain. De ce fait, de nombreuses recherches sont menées pour trouver des méthodes alternatives ou « proxy » pour la mesure indirecte du méthane. Mon travail de thèse a pour objectif de rechercher des marqueurs associés à la production de méthane chez la vache laitière, par une approche métabolomique multiplateforme. Ces marqueurs, une fois validés, pourront être dosés par des méthodes simples de laboratoire et appliqués à grande échelle pour évaluer les émissions de méthane. Étant donné le caractère exploratoire de l’approche et pour maximiser nos chances de réussite, nous avons combiné l’utilisation d’un inhibiteur spécifique de la méthanogènèse et l’analyse des profils métaboliques de quatre matrices (le lait, le plasma, le contenu ruminal et les urines)  avec différentes plateformes analytiques complémentaires : la résonnance magnétique nucléaire et la chromatographie liquide couplée à la spectrométrie de masse. Les échantillons biologiques proviennent d’une expérimentation animale utilisant 25 vaches Holstein primipares, et séparées en deux groupes suivant la présence ou non de l’additif anti-méthane dans la ration. Nous avons mesuré une diminution des émissions de méthane de 22,7% chez les animaux ayant reçu l’additif. Les analyses statistiques multivariées ont montré des profils métaboliques différents entre les 2 groupes d’animaux dans le plasma (27 métabolites discriminants) et le lait (16 métabolites discriminants). Les travaux sur les urines et le contenu ruminal sont en cours. L’analyse des réseaux métaboliques a mis en évidence plusieurs voies métaboliques impactées par la réduction des émissions de méthane impliquées dans le métabolisme énergétique ou encore dans celui des acides-aminés. / Ruminants produce significant amount of enteric methane, which is a major contributor of greenhouse gas emissions from agricultural origin. This production also results in a loss of 6 to 8% of the energy present in the diet. The reduction of enteric methane emissions from ruminants is an active area of research that requires the use of expensive, constraining measurement methods such as respiratory chambers or the use of a tracer gas that are difficult to use outside experimental farms. Therefore, there is a need of alternative, non-invasive measurement methods that can be used on large number of animals. In this work, we used an open metabolomic approach for identifying potential metabolic biomarkers associated with the production of methane in dairy cows. These discriminant metabolites, once validated, may be used for monitoring methane emissions under field conditions. To maximize the chance of finding such biomarkers, we used a multiplatform metabolomics approach (nuclear magnetic resonance and mass spectrometry) to better cover the metabolome and analyzed four biological matrices, namely milk, plasma, ruminal fluid and urine. We carried out a study involving 25 primiparous Holstein dairy cows that were divided into two groups fed a diet with or without a specific anti-methanogenic compound. We measured 22.7% reduction of methane emissions in the Treated group compared to the Control group. We identified 27 discriminant metabolites in plasma and 16 discriminant metabolites in milk. Metabolic network analysis highlighted pathways involved in energy and amino acids metabolism suggesting a general effect on the host animal induced by a reduction in methanogenesis.

Rumen protected Methionine (MET) and Lysine (LYS) are critical for milk protein synthesis in dairy cows. N-acetyl-L-methionine (NALM) is a MET derivative that consists of L-Met protected with an acetyl group that is attached to the α-amino group.N-acetyl-L-lysine (NALL) is a LYS derivative that is similarly protected. The objectives of these studies were to quantify the gastrointestinal availability of NALM and NALL. Three experiments were run as 3 × 3 Latin square using 3 second lactation Holstein cows that have been fitted with cannulas in the rumen and duodenum. The cows were fed diets containing the supplements for two weeks prior to each experiment so that the rumen microbes had time to adjust to the supplement. Each period consisted of 10 d of adaptation followed by 2 d of sampling. A dose of 0, 30, or 60 g of NALM was placed under the rumen mat at the time of feeding every day during experiment 1. The cows were similarly supplied with 0, 60, or 120 g of ƐNALL during experiment 2. The cows were supplemented with 0 g, 120 g ofƐNALL, or 120 g of diNALL during experiment 3. On day one of sampling, a liquid marker (Co-EDTA) was also administered at the time of the protected AA administration. Blood, ruminal, and duodenal samples were taken at hours 0, 1, 3, 6, 9, 12, and 24 post-feeding. There were no differences for milk production, milk protein, milk fat, or DMI for NALM or either NALL. There were no differences for ruminal escape (69.1% and 46.2% respectively) and duodenal appearance (2.16% and 3.40% respectively). The ruminal escape of ƐNALL was not different between the 120 g dose (32.7%) and the 60 g dose (27.2%). Duodenal appearance was higher (P < 0.01) for the 60 g dose (2.86%) than for the 120 g dose (1.19%) of ƐNALL. Acetate, propionate, butyrate, and valerate were higher (P < 0.01) for the supplemented cows during experiment 1 with NALL. There were no differences between ƐNALL and diNALL for rumen escape, duodenal appearance, VFA production, or blood LYS AUC. Results of the experiment verify significant protection of the N-acetyl MET and LYS from rumen degradation.