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L’endométrite est une maladie affectant les performances en reproduction chez la vache laitière. Elle est définie par la présence d’inflammation excessive au niveau de l’utérus durant la période post-partum. Le traitement antibiotique sous forme d’infusion intra-utérine est l’une des approches curatives les plus utilisées et améliore les performances de reproduction subséquentes. Considérant les enjeux modernes en lien avec l’antibiorésistance et la réduction de l’utilisation d’antibiotiques en productions animales, il est justifiable de remettre en question l’utilisation d’une méthode diagnostique de l’endométrite basée uniquement sur la présence d’inflammation en vue de déterminer si un traitement antibiotique doit être utilisé. En ce sens, l’objectif principal de ce projet de recherche était de valider l’exactitude des résultats de milieux de culture bactériologique utilisés à la ferme (Tri-plate et Petrifilm) en se basant sur ceux obtenus en laboratoire diagnostique. Un objectif secondaire était de vérifier la concordance entre les résultats bactériens de laboratoire et ceux cytologiques. Pour ce faire, une étude observationnelle transversale a été réalisée au sein de deux troupeaux laitiers commerciaux faisant partie de la clientèle de la Clinique ambulatoire bovine de la Faculté de médecine vétérinaire de l’Université de Montréal. Un total de 189 vaches en période post-partum (30 à 43 jours de lactation) ont été enrôlées de façon systématique afin de recueillir 2 échantillons utérins à partir de cytobrosses lors d’un même examen. La première cytobrosse était utilisée pour inoculer directement le milieu de culture Tri-plate et ensuite être envoyée au laboratoire du Service diagnostic de la FMV de l’Université de Montréal pour culture bactérienne aérobique. La seconde cytobrosse était utilisée pour l’analyse cytologique (proportion de cellules polymorphonucléaires; PMNL), puis était diluée dans 1 ml de solution saline pour inoculer le milieu Petrifilm. Après une période d’incubation de 24h, le décompte de colonies était fait pour chaque milieu de culture. À partir de ces données, les analyses statistiques ont été complétées dans le but d’optimiser la sommation de sensibilité et spécificité (Se+Sp) des deux milieux de culture en fonction des résultats du laboratoire de référence. Pour le milieu Tri-plate, le seuil de ˃ 90 colonies a permis d’obtenir la Se+Sp maximale, soit 167,7. Pour le milieu Petrifilm, le seuil de ˃100 colonies a donné la Se+Sp maximale, soit 129. En ce qui concerne la concordance entre le diagnostic cytologique et bactériologique, les résultats de notre projet montrent que 64,3% des vaches positives au niveau cytologique (˃6% PMNL) se sont avérées négatives à la culture bactérienne, démontrant un manque de concordance. En conclusion, les résultats de notre étude supportent la faisabilité et le potentiel de la culture bactérienne d’échantillons de l’endomètre à la ferme. Notre projet met également en évidence que l’utilisation d’un dépistage cytologique de l’endométrite afin d’utiliser un traitement antibiotique puisse causer un manque d’optimisation dans l’efficacité des traitements. Il semble donc pertinent que d’autres projets soient complétés afin d’approfondir le dépistage bactériologique de l’endométrite et d’analyser le potentiel diagnostique de celui-ci., Endometritis is a disease affecting reproductive performance in dairy cows. It is defined by the presence of excessive inflammation in the uterine body during the postpartum period. From a curative point of view, the use of antibiotic treatment in the form of intrauterine infusion is one of the most widely used methods which has a beneficial effect on subsequent reproductive performance in positive cases of endometritis. Considering the modern issues concerning the use of antibiotics in animal production, the use of a diagnostic method based on the presence of inflammation in order to administer antibiotic treatment is questionable. In that sense, the main objective of this research project was to validate the accuracy of the results of bacteriological culture medium used on the farm (Tri-plate and Petrifilm) based on the ones from diagnosis laboratory. A secondary objective was to verify the concordance between the bacterial and cytological results. To do this, a cross-sectional observational study was set up within two commercial dairy herds followed by the bovine outpatient clinic of the Faculty of Veterinary Medicine of the Université de Montréal. A total of 189 cows in the postpartum period (30 to 43 days in milk) were systematically enrolled in order to collect 2 uterine samples from cytobrush during the same examination. The first cytobrush was used to directly inoculate the Tri-plate medium and then be sent to the reference laboratory (Diagnostic service of the FVM of the Université de Montréal) for aerobic bacterial analysis. The second cytobrush was initially used to make a microscopic smear for cytological analysis (polymorphonuclear cell proportion (PMNL)) and subsequently diluted in 1 ml of saline to inoculate the Petrifilm medium. After an incubation period of 24 hours, the colony count was made for each culture medium. From these data, statistical analyses were completed in order to optimize the summation of sensitivity and specificity (Se + Sp) of the two culture medium according to the results of the reference laboratory. For the Tri-plate medium, the cutoff of ˃ 90 colonies resulted in the maximum Se + Sp, which was 167.7. For the Petrifilm medium, the threshold of ˃100 colonies gave the maximum Se + Sp, which was 129. Regarding the concordance between the cytological and bacterial diagnosis, the results of our project show that 64.3% of cows positive for cytological criteria (˃6% PMNL) were found to be negative from a bacterial point of view. In conclusion, this study shows that Tri-plate and Petrifilm medium used on-farms were best to reproduce the results obtained by laboratory analysis using 90 and 100 colony threshold respectively. Our results also support a lack of agreement between cytological and bacterial diagnosis. It therefore seems relevant that other projects are completed in order to deepen the bacterial screening for endometritis and to analyze its diagnostic potential.

During lactations, dairy cows faces huge calcium requirements due to milk production. Because of the fast increase in those requirements at the beginning of the lactation, the organism of dairy cows can hardly adapt by increasing intake and digestive calcium absorption. The organism must mobilize calcium from its storage pool, bones, which will replenish later in lactation. Those cycles of bone mobilization and reconstitution remain impossible to quantify for important number of dairy cows and the consequences of an incomplete bone reconstitution on following lactation remain unknown. The aim of this PhD was to develop an indicator of the phenomenon of bone mobilization and reconstitution during lactation.Several factors increasing bone mobilization have been identified, such as breed, parity or diet. However, the cycles of bone mobilization and reconstitution could not be related to variation in milk Ca and P content. However, it has been showed that, an insufficient Ca supply in early lactation does not always induce a higher bone mobilization, as it has been described in the literature, but can be compensated by an increase in digestive absorption capacity. The thesis also showed the need to quantify the consequences on insufficient dietary calcium supply on dairy cows’ milk production and health throughout lactation.; Au cours de leur lactation, les vaches laitières font face à d’importants besoins en calcium du fait de la production laitière. L'augmentation très rapide de ces besoins en début de lactation fait que l’organisme des vaches peut difficilement s’adapter par une hausse de l’ingestion et de l’absorption digestive de calcium. L’organisme doit puiser dans les réserves osseuses, qui seront reconstituées plus tard en fin de lactation. Ces cycles de mobilisation et reconstitution osseuses restent cependant impossibles à quantifier chez la vache laitière sur de larges effectifs et les conséquences d’une mauvaise reconstitution osseuse sur les lactations suivantes restent inconnues. Cette thèse avait pour objectif de développer un indicateur des phénomènes de mobilisation et reconstitution osseuse au cours de la lactation.Plusieurs facteurs de mobilisation osseuse ont pu être identifiés, comme la race, la parité ou l’alimentation. Cependant, les cycles de mobilisation et de reconstitution osseuse n’ont pas pu être reliés à des variations de la composition du lait en Ca et P. Il a cependant pu être montré, que contrairement à ce qui est décrit dans la littérature, un apport insuffisant en Ca en début de lactation n’est pas toujours accompagné d’une augmentation de la mobilisation osseuse, mais peut être compensé par une augmentation des capacités d’absorption digestive. Cette thèse montre aussi la nécessité de quantifier les conséquences d’un apport insuffisant de calcium alimentaire sur les performances de production et la santé des vaches laitières sur l’ensemble de la lactation.

Le méthane (CH4) est un puissant gaz à effet de serre produit lors de la fermentation microbienne anaérobie des aliments dans le rumen. L’un des enjeux majeurs pour le secteur de l’élevage est de trouver des stratégies (alimentaires, génétique) pour réduire les émissions de CH4 tout en maintenant les performances animales. Les techniques de mesure de ces émissions sont coûteuses et difficilement utilisables à grande échelle sur le terrain, d’où la nécessité de trouver des alternatives de mesure ou biomarqueurs pour prédire ces émissions. Les acides gras (AG) du lait ont déjà été identifiés comme indicateurs intéressants de la méthanogenèse chez la vache laitière, mais il convient d’améliorer la précision des équations de prédiction du CH4 existantes ainsi que d'élargir leur domaine d'application à tous types de rations. L'objectif de mon travail de thèse a été de confirmer la pertinence des AG du lait comme indicateurs périphériques de la méthanogénèse chez la vache laitière avec diverses conditions nutritionnelles. Deux bases de données regroupant des données individuelles (issues d’une collaboration scientifique internationale) et moyennes (issues de la littérature) de CH4, de composition en AG du lait et d’autres performances et caractéristiques de l’animal, ainsi que des données de composition chimique des rations, ont été créées. Parallèlement, l’acquisition in vivo de données en conditions expérimentales contrôlées pour des rations mal connues ont permis d’incrémenter la base de données individuelles. Des équations de prédiction des émissions de CH4 [en g/jour, g/kg de matière sèche ingérée (MSI), et g/kg de lait] ont été développées à partir de certains AG du lait, utilisés seuls ou combinés à d’autres variables d’ingestion et de performances laitières, représentant alors des modèles complexes. Des relations entre les émissions de CH4 et la teneur de différents AG du lait (C10:0, iso C17:0 + trans-9 C16:1, iso C16:0, cis-11 C18:1, cis-15 C18:1, cis-9,cis-12 C18:2, et trans-11,cis-15 C18 :2) ont été mises en évidence, confirmant des voies métaboliques communes dans le rumen entre méthanogenèse et métabolisme lipidique. Les équations sont également liées aux types de régimes à partir desquels elles ont été développées. Les équations simples (AG du lait uniquement) sont moins précises que les complexes (erreurs résiduelles de prédiction, respectivement, de 58.6 g/jour, 2.8 g/kg MSI et 3.7 g/kg lait vs. 42.8 g/jour, 2.5 g/kg MSI et 3.3 g/kg lait). Une différence minimum de 16% de CH4 entre stratégies de réduction pourra être mise en évidence par la meilleure équation de prédiction développée. Des équations basées sur des AG bien déterminés par les méthodes infrarouges devront être testées pour évaluer, en routine et à grande échelle, de nouvelles stratégies de réduction des émissions de CH4 entérique chez la vache laitière., Methane (CH4) is a potent greenhouse gas coming from the anaerobic microbial fermentation of the diet in the rumen. One of the main current challenge for the dairy sector is to find CH4 mitigation strategies (diets or genetics) without altering animal performance. Enteric methane measurement methods are costly and very difficult to apply on a large scale on field. Thus, there is a need to develop alternative measurement methods, such as equations based on proxies to predict CH4 emissions. Milk fatty acids (FA) have been identified as potential predictors of the methanogenesis in dairy cattle, but the prediction ability of extant published CH4 equations must be improved, and their domain of applicability must be enlarged to a wide range of diets. The objective of this PhD thesis was to confirm the potential of milk FA as proxies to predict enteric CH4 emissions in dairy cows fed a wide range of diets. Two databases (based on individual and mean data, respectively) were built thanks to an international collaboration, and gathered data on CH4, milk FA composition, dairy performances, diet and animal characteristics. Two in vivo experiments were conducted with the aim to study the effect of dietary strategies poorly documented, on methanogenesis and milk FA. The data from these experiments were included in the created database. Firstly, simple CH4 prediction equations were developed [g/d, g/kg of DMI (DMI), and g/kg of milk] based only on milk FA, and secondly other variables related to cow intake or characteristics, and dairy performance were added and constituted complex equations. Relationships between CH4 and several milk FA (C10:0, iso C17:0 + trans-9 C16:1, iso C16:0, cis-11 C18:1, cis-15 C18:1, cis-9,cis-12 C18:2, and trans-11,cis-15 C18 :2) were found, confirming common rumen metabolic pathways between methanogenesis and lipid metabolism. Equations were also closely related to the diets included in the database used for their development. Simple equations were less accurate than complex ones (prediction error of 58.6 g/d, 2.8 g/kg DMI and 3.7 g/kg milk vs 42.8 g/d, 2.5 g/kg DMI and 3.3 g/kg milk, respectively). A minimum difference of 16% in CH4 emissions between mitigating strategies can be evidenced with the best prediction equation developed in this PhD. Methane prediction equations based on milk FA well determined by infrared spectrometry methods need to be developed in order to be used on a routine basis and on a large scale. These prediction equations would allow studying the effect of novel mitigation strategies of enteric CH4 emissions in dairy cows.

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Simulation of the variation in grass growth, milk production and residency time in a 40 hectare farm composed of either 6 or 40 paddocks. 10. International Symposium on the Nutrition of Herbivores (ISNH)

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Supplementing with grass silage or restricting pasture: strategies to overcoming short term feed deficits in the diet of early lactation dairy cows in early spring. 10. International Symposium on the Nutrition of Herbivores (ISNH)

Complete nitrogen balance in dairy cows: does every drop of sweat count?. 10. International Symposium on the Nutrition of Herbivores (ISNH)

In ruminants, the early phase of drying-off is a period of mammary gland involution that is marked by the cessation of prolactin (PRL) release. The speed at which the bovine mammary gland involutes following the abrupt cessation of lactation is directly related to the risk of new intramammary infections.[br/] Objectives[br/] Our aim was to assess the effect of PRL inhibition by cabergoline on the speed of the mammary gland involution, through analysis of the changes of mammary secretion composition.[br/] Materials and methods[br/] Fourteen Holstein dairy cows were injected with a single i.m. administration of 5.6 mg cabergoline (n=7) (Velactis ®, Ceva Sante Animale) or placebo (n=7) at the first day of dryingoff (D0). Mammary secretion samples were collected using a teat-cannula once during lactation (D-6) and at D1, D2, D3, D4, D8 and D14 after the drying-off. The mammary secretion samples were used for milk fat, lactose, true protein, alpha-lactalbumin and SCC analysis. Mammary biopsy samples were collected one week before drying-off (D-6), at D1 and at D8 and used for RNA extraction and RT-PCR analyses.[br/] Results[br/] As expected, SCC progressively increased whereas lactose content decreased in mammary secretions after drying-off (P < 0.001). The increase in SCC was 2.4 fold higher in cabergoline treated cows than in control cows (P < 0.01). The decrease of lactose content in mammary secretions progressively decreased during involution and was associated with paralleled change in GLUT-1 mRNA level coding the main glucose transporter in the udder. These decreases were faster in cabergoline treated cows compared to controls with lower lactose content in cabergoline treated cows already by D1 than in controls (P < 0.05) and significant decrease in GLUT-1 mRNA levels at D1 and D8 respectively for cabergoline and control treatments compared to D-6 (P ≤ 0.05). Cabergoline treatment tended to increase fat content at D3 after drying-off (P < 0.10). No significant effects of cabergoline treatment were observed both in true protein and in alpha-lactalbumin contents in mammary secretions or in alphalactalbumin and kappa-casein mRNA levels in mammary tissues.[br/] Conclusions[br/] The changes in lactose, SCC and fat in mammary secretions and GLUT-1 mRNA level in the udder, indicate that cabergoline treatment was efficient to hasten the mammary gland involution without affecting milk protein synthesis in the mammary tissue. Cabergoline could facilitate dairy management at the time of dry-off.

ObjectivesIn ruminants, the early phase of drying-off is a period of intense mammary gland involution that is due, in part, to dramatic decline prolactin (PRL) release. The speed at which the bovine mammary gland involutes following the abrupt cessation of lactation is also directly related to the risk of new intramammary infections. Thus, strategies to hasten involution following dry-off could have implications in preventing mastitis and optimizing mammary tissue regenerative processes.Materials and methodsTo assess the effect of prolactin inhibition by cabergoline on mammary gland involution, 14 Holstein dairy cows were injected with a single i.m. administration of 5.6 mg cabergoline (n=7) or placebo (n=7) within 4 hours after the last milking before the drying off at the day of drying-off (D0). Mammary secretion samples were collected using a teat-cannula once during lactation (D-6) and at D1, D2, D3, D4, D8 and D14 after the drying-off. The mammary secretion samples were used for lactoferrin and zymography analyses to detect the activity of enzymes such as MMP, matrix metalloproteinases involved in the remodelling of mammary tissue during involution. Mammary epithelial cells (MEC) were also purified from mammary secretions after centrifugation andimmunocytochemical binding in order to evaluate the MEC exfoliation. Mammary biopsy samples were collected one week before drying-off (D-6), at D1 and at D8 and used for lactoferrin immunochemistry and zymography analyses.ResultsThe activity of MMP9 increased after drying-off in mammary secretions (P < 0.001). Cabergoline increased the activity of MMP9 (1.7 fold, P < 0.05) in mammary secretions and MMP-2 in mammary tissue after drying-off (1.4 fold, P ≤ 0.01). MEC concentration progressively increased in mammary secretions after drying-off (P < 0.01). Cabergoline induced an increase in MEC concentration (P =0.04). Lactoferrin content progressively increased in mammary secretions during involution. The rise of lactoferrin content in mammary secretions was significant starting at D4 in the cabergoline treated cows (P ≤0.05) whereas it only happened at D8 in controls (P < 0.05). Overall, cabergoline treatment increased lactoferrin content of mammary secretions (P = 0.10). The total lactoferrin immunostaining in the mammary tissue increased after drying-off (P < 0.05). Compared with during lactation, this increase was observed at D1 and D8, respectively for cabergoline treated cows and control cows (P

Lipolysis is an enzymatic reaction which leads to off-flavour in milk and impairs technological properties of milk. Lipolysis corresponds to the hydrolysis of milk fat located in milk fat globules (MFG) by the lipoprotein lipase (LPL) and its cofactors, leading to free fatty acid accumulation. Variability of spontaneous lipolysis (SL) levels depend on individuals and on breeding systems. Five trials were set up to understand SL variations. The effect of breed, parity, physiological stage, milking frequency, milking time, feeding systems and lipid supplementation on SL were evaluated by continuous designs. The effects of milking time, feeding restriction and nature of forage on all enzymatic system were evaluated by two cross-over studies. Data were analysed using linear models. Cows from the five trials could be classified in two groups according to their phenotype: ‘susceptible’ and ‘non-susceptible’ to SL, confirming the strong impact of the individual effect. Among ‘susceptible’ cows, we confirmed the effects of breed, parity, physiological stage, milking time, milking frequency and feeding systems. SL was higher in Holstein cows’ milk than in Normande cows’ milk (P

Milk production is highly dependent on the extensive expansion of the mammary epithelium which largely occurs during puberty. Within the mammary epithelium, the Mammary Stem Cells (MaSC) and their progeny play a key role in driving the development of the future functional mammary gland. Later, these cells contribute to regenerate the secretory epithelium in order to ensure future lactations. To elucidate the epithelial cell lineage involved in the establishment of the functional gland, we investigated the MaSC/progenitors populations in the bovine mammary tissue at various physiological stages. We used flow cytometry to phenotype epithelial cells on the basis of CD49f and CD24 expression in animals at three contrasted physiologic stages: puberty (heifers of 17 months of age), lactation (multiparous cows producing 35 kg of milk) and drying off (cows at 6 years after drying off). Comparison of the cytometric profiles highlighted the presence of a distinct epithelial population of CD49flowCD24pos cells at puberty (23.7%±3.6) which substantially decreased in the others stages (4.1%±1 at lactation and 6%±1 at drying off). These CD49flowCD24pos cells had features of a dual lineage, with luminal and basal characteristics (CD10, ALDH1 and keratin 7 expression) and were considered to be early common progenitors. The MaSC fraction was recovered in the sub-population of CD49fhighCD24pos cells. When cultured in vitro (in a 3D culture system with matrigel), these cells formed mammospheres, a functional property of MaSC. At puberty, total mammary cells contained 2.8%±0.3 of MaSC. This proportion of MaSC was significantly reduced at lactation (1.1±0.3%) and at drying off (0.4±0.3%). Further phenotypic characterization of the CD49fhighCD24pos cells showed that they expressed CD10 and keratin 14 at any stages. This in-depth characterization of the epithelial sub-populations at various physiological stages provide new insights into the epithelial cell hierarchy in the bovine mammary gland from puberty to drying off.

In dairy farms calves and cows are usually separated shortly after birth but this practice raises the question of animal welfare. This social concern may lead to bring back dairy calves to their mother. Even though suckling is quite seldom in dairy production, some farmers are using such a practice for many years. The present study aims to better know farmer’s motivations, practical implementation and farmer’s perception of the impact of suckling on performance and animal behaviour. In January 2018 a semi-quantitative survey was performed on 44 farms where calves suckle at least 24 hours their mother or a nurse cow. The farming systems differed on the size (20 to 140 cows), the type (19 conventional, 25 organic farms), the suckling (28 by the mothers, 16 by nurses), and the breed. Results indicate that main farmers’ motivations are calves’ health (52%), better working conditions (41%) and saving time (34%), with little consideration on animal welfare (7%). Numerous practices were found in terms of allowance of daily cow-calf contact and suckling duration with a difference between male and female calves. According to farmers, these practices were efficient to improved calves’ health (70%), save time (75%) and improved working conditions (52%). Weaning was considered as a stressful situation, especially after long suckling periods. Cow mooing usually stopped 2.5 d after weaning. At least 34 farmers are fully satisfied with this practice. The main challenge appears to be the management of the wildness of future heifers, by investing time to manipulate calves before weaning. The results of this survey could help to propose solutions to farmers who want to cope with the societal demand of keeping calves with dams in dairy herds.

Increasing by-pass protein is one of the challenges of ruminant nutrition to both cover the protein needs of animals and reduce the nitrogen excretion in the environment. Industrial process such as heat treatment, formaldehyde tanning and vegetable extract are focused on the protection of proteins against ruminal fermentations but show some limits (low intestinal digestibility, toxicity, low or variable efficiency). The reduction of the mean retention time (MRT) by varying size and density of particle is another way to increase by-pass protein fraction of concentrates. Plastic particles of four sizes (0.5, 1, 2 and 3 mm) and four densities (0.9, 1.1, 1.3 and 1.5) were used to study the combined effect of size and density on MRT of particles without microbial fermentation interactions. The kinetics of faecal excretion of particles (17 sampling over 106 hours) were studied in a Latin square experiment including four lactating cows. Data were adjusted to a double exponential model. Density has a quadratic response with the fastest escape for densities 1.1 and 1.3 in the total digestive tract (TMRT=29.5 and 31.2 hours respectively) as well as in the compartments isolated by the model compared to densities 0.9 and 1.5 (TMRT=64.0 and 51.2 hours respectively). Size has a linear effect on the total digestive tract transit time (+12.9 hours for the 3 mm size compared to the 1 mm) and in the time of first appearance of particles but no effects were observed in the others compartments. A combined effect of size and density is observed: particle size has no effect on TMRT when density is between 1.1 and 1.3 butoutside this range, an increase of particle size induces an increase in the TMRT. In conclusion a density in a range 1.1 to 1.3 will be optimal for the by-pass of particles of concentrate. These particles will be submitted to ruminal fermentations, and their optimal size must be small enough to pass the reticulo-omasal orifice but large enough todelay the start of fermentation on their surface and thus the loss of density by fermentation gases production. Size 3 to 4 mm would be a good compromise between these two constraints to allow the shortest escape from the rumen.

New processes to increase the proportion of by-pass protein from feeds for ruminant are emerging (essential oils, natural tannins). However, the traditional methodologies used to predict nutritional value (degradation in vitro or in sacco) are not suitable with these new techniques that claim more systemic effects in rumen. The objective of this trial was to test the biological milk protein response to the supply of metabolizable protein as a new methodology for assessing the protein value of feed. This biological response is not linear because the efficiency of metabolizable protein (milk protein/metabolizable protein intake) decreases when the protein supply increases. We assumed a linear decrease of protein efficiency to be able to predict the protein value of a diet from the observed milk production with only two reference extreme diets of known feed value. Four isoenergetic treatments, defined by their protein supply, were applied in a Latin square design to 24 cows divided in 6 homogenous groups (based on potential production of cows and parity) over four 3-wk periods. The two extreme treatments contained either 3.4 kg DM of energetic concentrate (C++S0, 101 g PDIE/kg MS) or 3.4 kg DM of soybean meal (C0S++, 242 g PDIE/kg MS). Two intermediary diets with mixes of these two feeds (C++S+, 152 g PDIE/kg MS and C+S++, 199 g PDIE/kg MS) where used to assess their metabolizable protein from their milk protein responses. Increasing protein supply has a significant positive effect on milk protein yield (895 and 964 g protein.d-1 for C++S0 and C0S++ respectively). Estimation of the protein value of the two intermediate diets according to the milk protein response were 17 and 15 g PDIE.kg MS-1 higher for C++S+ and C+S++ respectively than the calculated one (i.e. an error of 11 and 7% respectively). This error could be partly explained by small differences in energy intake. In spite of this slight overestimation, milk protein response seems a relevant approach, independent of the protection process, to estimate the protein value of feed, especially for the new feed protections.

International audience; The mammary tissue is characterized by its capacity to adapt in response to a wide variety of changing conditions. This capacity of adaptation refers to the mammary tissue plasticity. In dairy ruminants, lactation is challenged by modifications that can either be induced on purpose such as modifications of management practices, or involuntary when adverse environmental constraints arise. These modifications can elicit both immediate changes in milk yield and composition and carryover effects that persist after the end of the challenge. This review focuses on the current knowledge concerning the cellular mechanisms underlyingmammary tissue plasticity. One of the main cellular mechanisms contributing to mammary tissue plasticity is the changes in the activity and number of mammary epithelial cells in the tissue. The later results from changes in the rates of cell proliferation and death, as well as changes in mammary epithelial cell exfoliation. It also relies on the number of resident adult mammary stem cells and their progenitors, which can regenerate the pools of mammary cells. Epigenetic changes may stand for an additional mechanism. Several challenges including the milking frequency, the level of feed supply and hormonal manipulations have been shown tomodulate milk yield together with changes in mammary cell activity, turnover and exfoliation. Changes in DNA methylation have been observed together with reductions in milk yield during once daily milking and during mastitis in dairy cows, and may affect cell activity sustainably. In contrast to what has been assumed for a long time, no carryover effect on milk yield were observed during challenges induced by the level of feed supply in dairy cows and milking frequency in dairy goats, even if the number of mammary cells was reduced. In addition, the mammary tissue plasticity have been shown to be influenced by the parity, the stage oflactation, the health status and genetic factors. In conclusion, the cellular mechanisms underlying mammary tissue plasticity are diverse and the mammary tissue can either shows elastic properties (with no permanent deformation) or not in response to environmental changes.

International audience

National audience

International audience; Efficiency of utilization of amino acid increased with energy supply at low and high metabolizable protein supply in dairy cows. Adsa Annual Meeting

This study aimed to explore the effect of alternative selection strategies based on milk fat and protein contents instead of milk yield on reproduction of dairy cows. About 500 lactations were recorded, equally distributed among breeds (Holstein: HO or Normande: NO) and genetic groups with similar genetic merit for fat and protein yields and either high breeding values for milk yield (MILK) or fat and protein contents (CONT). Milk progesterone monitoring enabled the study of the reproductive performance. In both breeds, cows in CONT produced less milk (-763 kg in HO, -649 kg in NO), with higher fat content (+4.1 g kg-1 in HO and +3.9 g kg-1 in NO) and higher protein content (+1.6 g kg-1 in HO, +2.0 g kg-1 in NO) than cows in MILK. Cows in CONT had an earlier resumption of luteal activity than cows in MILK (-6 d in HO, -4 d in NO). There was no difference in ovulation detection rates between genetic groups. No difference in fertility performance was observed between genetic groups in NO. However, HO in CONT had a lower re-calving rate than in MILK (48 vs 55%). Selecting dairy cows for fat and protein contents may not be a good opportunity to improve reproduction.

This study aimed to explore adaptive trajectories of dairy and dual purpose breeds in contrasting grazing-based feeding systems (FS). About 500 lactations were recorded at the INRA farm of Le Pinau- Haras, equally distributed among breeds (Holstein: HO or Normande: NO) and FS (High or Low). It was possible to study the different steps of the reproductive process by combining milk progesterone information (three times a week) with intensive oestrous behaviour recording and pregnancy diagnosis (ultrasonography). Holstein produced more milk (+2294 kg in the High FS, +1280 kg in the Low FS) and lost more body condition than NO. Cows in the Low FS produced less and lost more body condition than in the High FS. NO resumed ovarian activity earlier (-5 d) and showed a higher proportion of normal cyclicity patterns (+22%) than HO. There was no difference in ovulation detection rates between breeds or FS. The NO had a higher re-calving rate than HO (+19%). Feeding system was not associated with cyclicity and re-calving rate. By limiting their milk yield, NO did not experience a severe negative energy balance, unlike HO. This resulted in better reproductive performance for NO, suggestive of greater suitability to a compact calving system.

The objective of the experiment was to quantify the effect of stocking rate (SR) and breed on milk production, dry matter intake (DMI) and milk production efficiency across two consecutive grazing seasons (2014 - 2015) in an intensive spring calving system. Dry matter intake records were available for 68 Holstein-Friesian (HF) and 71 Jersey × Holstein-Friesian (J×HF) cows in each year of the experiment. Cows within each breed were randomly allocated to one of three SR treatments defined in terms of bodyweight (BW) per hectare (kg BW ha-1): low (LSR; 1,200 kg BW ha-1), medium (MSR; 1,400 kg BW ha-1), and high (HSR; 1,600 kg BW ha-1). Individual cow DMI was estimated three times per year: spring (March), summer ( June) and autumn (September). The effect of SR, breed, season and their interactions were analysed using mixed models. Milk production, BW and milk production efficiency per cow decreased significantly as SR increased due to reduced herbage availability per cow and increased grazing severity. As a percentage of BW, J × HF cows had greater DMI, milk solids production and milkproduction efficiency.

The objective of this experiment was to investigate if different pasture allowances offered to early lactation(40 days in milk at experiment start) grazing dairy cows for varying time durations influenced dry matterintake (DMI) measured at weeks two, six and 12 of the experiment. The two year experiment offeredcows one of four pasture allowances (PA; 60, 80, 100 or 120% of intake capacity; IC) for either twoor six weeks; PA was based on the 100% IC treatment, as their DMI increased all other PA increasedproportionately. Once the two- and six-week time durations had elapsed, all cows were offered 100% IC.Dry matter intake was estimated using the n-alkane technique. Data were analysed using mixed modelsin PROC MIXED (SAS; v9.4). There was a linear response to PA when DMI was measured at two andsix-weeks; for every 10% increase in PA, DMI increased by 0.65 and 0.56 kg cow-1 day-1, respectively.At six weeks there was no difference in DMI of cows offered differing PA for a two week duration (15.4kg cow-1 day-1). When all cows were offered 100% IC and DMI was measured at week 12, there was noeffect of PA or duration on DMI (16.5 kg cow-1 day-1). This suggests that in early lactation there is aneffect of PA on DMI but any effects disappear when cows are offered 100% IC.

Grass availability in spring is highly variable. Including grazed grass in the diet of early lactation dairy cows can result in improved animal performance. The objective of this experiment was to determine if a high opening farm cover (OFC) can impact on early lactation milk production in a spring calving system. In spring 2017 (6 February – 25 April), 45 cows were randomly assigned to one of three (n = 15) OFC; High (H) (974 kg DM ha-1), Medium (M) (863 kg DM ha-1) and Low (L) (624 kg DM ha-1). All cows were allocated an equal daily grazing area. Post-grazing sward height and daily herbage allowance (DHA) were measured daily and pre-grazing herbage mass (> 3.5 cm) twice weekly. Milk yield was recorded daily and composition once weekly. There was a significant effect of treatment on daily milk yield (P < 0.05); the H treatment had greater production than the M treatment (+1.9 kg cow-1). Milk composition did not differ with treatment. Daily herbage allowance was greater (P > 0.05) on the H treatment than the L treatment, with the M treatment intermediate. Higher OFC increases grass availability on the farm which increases DHA, resulting in increased milk production performance.

Herbage utilisation is of primary importance to grassland farmers due to its strong association with profit, yet it is not assessed in routine grass evaluations. On commercial grassland farms, grazing efficiency of varieties is believed to influence their level of herbage utilisation. To understand grazing efficiency the interaction between plant and animal is critical; mechanically simulated grazing protocols are limited in the information they provide. The objective of this paper was to further understand the grazing efficiency of perennial ryegrass varieties by identifying grazing traits which can be used as selection criteria by breeders striving to develop varieties with improved herbage utilisation. Fifty-five perennial ryegrass varieties, both diploid and tetraploid with intermediate and late heading dates, were sown in plots (3 m x 7 m; 21 m(2)) following a randomised block design with three replicates per variety. Swards were rotationally grazed by lactating dairy cows during the 2015 and 2016 grazing seasons. Sward structural, morphological, and chemical characteristics were measured and related to grazing efficiency, as measured by post-grazing sward height. These data were analysed using the PROC MIXED procedure to test the fixed effects of traits and the GLM procedure to test their relationships with grazing efficiency. Varieties were shown to differ in their level of grazing efficiency (p < 0.001). Tetraploid varieties had significantly (p < 0.001) greater grazing efficiency than diploids recording post-grazing sward heights of 3.8 and 4.1 cm, respectively. Increased free leaf lamina (p < 0.001), tiller mass (p < 0.05) and dry matter digestibility (p < 0.01) were shown to significantly improve grazing efficiency of varieties. This study has identified free leaf lamina, tiller mass and dry matter digestibility as key selection criteria for plant breeders to base their developments upon if grazing efficiency is imported into their breeding programmes.

National audience

L’hypercétonémie est une maladie métabolique réduisant la profitabilité des entreprises laitières. Restreindre la production lactée brièvement après le vêlage pourrait diminuer son incidence. Ce travail étudie l’impact d’un protocole de traite incomplète en début de lactation sur la cétonémie, l’hypercétonémie et la réduction d’indice de l’état corporel. Avant le vêlage, 838 vaches Holstein multipares provenant de 13 troupeaux laitiers à vocation commerciale ont été aléatoirement assignées à un protocole de traite complète ou incomplète (traite de 10 à 14 kg de lait par jour pour les cinq premiers jours en lait). Hebdomadairement, la concentration sanguine des β-hydroxybutyrates était mesurée durant les trois premières semaines de la lactation. Une concentration du β-hydroxybutyrate ≥ 1.4 mmol/L a été utilisée pour définir l’hypercétonémie. Puisque plusieurs évaluateurs ont noté les indices de l’état corporel et que l’accord inter-observateurs de son évolution dans le temps n’avait jamais été étudiée, une seconde étude a été réalisée pour l’estimer. Le protocole de traite incomplète a réduit la cétonémie pour la période 4-7 jours en lait et tend à la réduire pour la période 8-17 jours en lait. Ce même protocole a réduit significativement l’hypercétonémie pour les périodes 4-7 et 8-17 jours en lait. L’étude menée parallèlement à l’étude principale révélait un accord inter-observateurs acceptable pour la variation de l’indice de l’état corporel. Aucune différence au niveau de la variation de l’indice de l’état corporel en début de lactation n’a été notée entre les deux protocoles de traite. En conclusion, cette stratégie est efficace pour réduire la cétonémie et l’hypercétonémie en début de lactation., Hyperketonemia is a metabolic disorder reducing profitability of dairy cattle. Restricting milk production shortly after calving could reduce its incidence. This study assessed the impact of an incomplete milking protocol in early lactation on ketonemia, hyperketonemia and loss of body condition score. Prior to calving, 838 multiparous Holstein cows from 13 commercial herds were randomly assigned to a complete or an incomplete milking protocols (milking 10-14 kg of milk per day for the first 5 days in milk). Ketonemia was evaluated weekly by measuring blood concentration of β-hydroxybutyrate during the first three weeks of lactation. A concentration of β-hydroxybutyrate ≥ 1.4 mmol/L was used to define hyperketonemia. Since several evaluators did assessments of body condition scores and because inter-observer agreement of its variation over time had never been studied, a second study was carried out to quantify agreement for this measure. The incomplete milking protocol has reduced ketonemia for the 4-7 days in milk period and has tended to reduce it for the 8-17 days in milk period. This protocol has reduced hyperketonemia for the 4-7 and 8-17 days in milk periods. The study that managed to quantify inter-observers agreement revealed an acceptable inter-observer agreement for variation of body condition score. The incomplete milking protocol was not associated with loss of body condition score. In conclusion, this strategy is effective in reducing ketonemia and hyperketonemia in early lactation.

Extruded linseed (EL), rich in α-linolenic acid, is a feed used in dairy cattle nutrition in order to modify milk fatty acid profile in a way to potentially improve human health. However, effects of EL on dairy cow performance are little documented. The objective was to assess the effects of EL supplementation on animal performance, then to estimate the economic consequences at a farm level. A meta-analysis (21 experimental trials) allowed us to characterize the variability of animal responses related to the quantity of EL and the basal diet composition. A cohort study performed on 1204 herds and 194056 cows displayed an association between quantity of EL and milk yield (+ 0.4 à +1,3 kg/d), and milk contents (-0,03 to -0,20 g/kg MPC and -0,1 to -0,9 g/kg MFC). Other beneficial associations were highlighted: a decrease in number of days open and a better probability to cure of intra-mammary infections. Finally, we demonstrated that a farmer willing to modify the fatty acid composition of the milk to improve human health face higher feed costs but can be rewarded by better animal performance that increase profitability of the farm.; La graine de lin extrudée (GLE), riche en acide α-linolénique, est un aliment utilisé en élevage bovin laitier pour modifier la composition en acides gras du lait vers un profil nutritionnel favorable à la santé humaine. Cependant, l’effet de la graine de lin sur les animaux est peu documenté. L’objectif était d’évaluer les effets de l’utilisation de la GLE sur les performances animales en élevage bovin laitier, puis d’en estimer les conséquences économiques au niveau de l’exploitation bovine laitière. Une méta-analyse (21 essais expérimentaux) a permis de caractériser la variabilité des performances laitières en conditions expérimentales selon la quantité de GLE et la ration associée. Une étude épidémiologique exposé/non exposé menée dans 1204 élevages sur 194056 vaches a montré une association entre la quantité de GLE et la production laitière (+ 0.4 à +1,3 kg/j) et les taux de matières utiles (-0,03 à -0,20 g/kg de TP et -0,1 à -0,9 g/kg de TB). D’autres associations ont été mises en évidence : amélioration de la fécondité et de la guérison des infections intra-mammaires. Enfin, par simulation, nous avons montré qu’un éleveur produisant un lait de meilleure qualité nutritionnelle via l’utilisation de la GLE dans les conditions d’utilisation de terrain était récompensé par un gain de marge de son atelier laitier via des effets zootechniques positifs malgré le surcoût alimentaire engendré.

Fluctuations in spring grass growth can create deficits in grass supply during the early lactation period in Irish dairy production systems. The objective of this experiment was to investigate if different pasture allowances offered to early lactation grazing dairy cows for varying time durations influenced cumulative milk yield and composition produced during the first 33 weeks of the experiment. The two-year experiment offered cows one of four pasture allowances (PA; 60, 80, 100 or 120% of calculated intake capacity) for either two or six weeks. Once the two- and six-week time durations had elapsed, all cows were offered 100% of intake capacity. Data were analysed using mixed models in PROC MIXED (SAS; v9.4). There was a tendency (P = 0.06) for an interaction between duration and PA for cumulative milk yield. Offering 120% for six weeks increased milk yield (4,270 kg cow-1) compared to 80 × 2, 100 × 2, 60 × 6 and 80 × 6. All cows other than the 120 × 6 were similar (3,957 kg cow-1). There was no effect of PA or duration on milk fat, protein and lactose content. This suggests that when cows are offered more than they require to achieve IC for a six-week period (120 × 6), cumulative milk yield is higher compared to those offered a restricted PA for an extended period of time (six weeks).

Precision technologies and data have had relatively modest impacts in grass-based livestock ruminant production systems compared with other agricultural sectors such as arable. Precision technologies promise increased efficiency, reduced environmental impact, improved animal health, welfare and product quality. The benefits of precision technologies have, however, been relatively slow to be realised on pasture based farms. Though there is significant overlap with indoor systems, implementing technology in grass-based dairying brings unique opportunities and challenges. The large areas animals roam and graze in pasture based systems and the associated connectivity challenges may, in part at least, explain the comparatively lower adoption of such technologies in pasture based systems. With the exception of sensor and Bluetooth-enabled plate metres, there are thus few technologies designed specifically to increase pasture utilisation. Terrestrial and satellite-based spectral analysis of pasture biomass and quality is still in the development phase. One of the key drivers of efficiency in pasture based systems has thus only been marginally impacted by precision technologies. In contrast, technological development in the area of fertility and heat detection has been significant and offers significant potential value to dairy farmers, including those in pasture based systems. A past review of sensors in health management for dairy farms concluded that although the collection of accurate data was generally achieved, the processing, integration and presentation of the resulting information and decision-support applications were inadequate. These technologies' value to farming systems is thus unclear. As a result, it is not certain that farm management is being sufficiently improved to justify widespread adoption of precision technologies currently. We argue for a user need-driven development of technologies and for a focus on how outputs arising from precision technologies and associated decision support applications are delivered to users to maximise their value. Further cost/benefit analysis is required to determine the efficacy of investing in specific precision technologies, potentially taking account of several yet to ascertained farm specific variables.

International audience; Residual feed intake, which is usually used to estimate individual variation of feed efficiency, requires frequent and accurate measurements of individual feed intake to be carried out. Developing a breeding scheme based on residual feed intake in dairy cows is therefore complicated, especially because feed intake is not measurable for a large population. Another solution could be to focus on biological determinants of feed efficiency, which could potentially be directly and broadband measurable on farm. Several phenotypes have been identified in literature as being associated with differences in feed efficiency. The present study therefore aims to identify which biological mechanisms are associated with residual energy intake (REI) differences among dairy cows. Several candidate phenotypes were recorded frequently and simultaneously throughout the first 238 d in milk for 60 Holstein cows fed on a constant diet based on maize silage. A multiple linear regression of the 238 d in milk average of net energy intake was fitted on the 238 d in milk averages for milk energy output, metabolic body weight, the sum over the 238 d in milk of both, body condition score loss and gain, and the residuals were defined as REI. A partial least square regression was fitted over all biological traits to explain REI variability. Linear multiple regression explained 93.6% of net energy intake phenotypic variation, with 65.5% associated with lactation requirement, 23.2% with maintenance, and 4.9% with body reserves change; the 6.4% residuals represented REI. Overall, measured biological traits contributed to 58.9% of REI phenotypic variability, which were mainly explained by activity (26.5%) and feeding behavior (21.3%). However, apparent confounding was observed between behavior, activity, digestibility, and rumen-temperature variables. Drawing a conclusion on biological traits that explain feed efficiency differences among dairy cows was not possible due to this apparent confounding between the measured variables. Further investigation is needed to validate these results and to characterize the causal relationship of feed efficiency with feeding behavior, digestibility, body reserves change, activity, and rumen temperature.

Effect of milking time, temperature and diet nitrogen level on milk composition of dairy cows and on some milk properties (freezing point, lipolysis and heat stability). 10. International Symposium on the Nutrition of Herbivores (ISNH)

National audience

Objectives[br/] In ruminants, the early phase of drying-off is a period of intense mammary gland involution that is due, in part, to dramatic decline prolactin (PRL) release. The speed at which the bovine mammary gland involutes following the abrupt cessation of lactation is also directly related to the risk of new intramammary infections. Thus, strategies to hasten involution following dry-off could have implications in preventing mastitis and optimizing mammary tissue regenerative processes.[br/] Materials and methods[br/] To assess the effect of prolactin inhibition by cabergoline on mammary gland involution, 14 Holstein dairy cows were injected with a single i.m. administration of 5.6 mg cabergoline (n=7) or placebo (n=7) within 4 hours after the last milking before the drying off at the day of drying-off (D0). Mammary secretion samples were collected using a teat-cannula once during lactation (D-6) and at D1, D2, D3, D4, D8 and D14 after the drying-off. The mammary secretion samples were used for lactoferrin and zymography analyses to detect the activity of enzymes such as MMP, matrix metalloproteinases involved in the remodelling of mammary tissue during involution. Mammary epithelial cells (MEC) were also purified from mammary secretions after centrifugation and immunocytochemical binding in order to evaluate the MEC exfoliation. Mammary biopsy samples were collected one week before drying-off (D-6), at D1 and at D8 and used for lactoferrin immunochemistry and zymography analyses.[br/] Results[br/] The activity of MMP9 increased after drying-off in mammary secretions (P < 0.001). Cabergoline increased the activity of MMP9 (1.7 fold, P < 0.05) in mammary secretions and MMP-2 in mammary tissue after drying-off (1.4 fold, P ≤ 0.01). MEC concentration progressively increased in mammary secretions after drying-off (P < 0.01). Cabergoline induced an increase in MEC concentration (P =0.04). Lactoferrin content progressively increased in mammary secretions during involution. The rise of lactoferrin content in mammary secretions was significant starting at D4 in the cabergoline treated cows (P ≤0.05) whereas it only happened at D8 in controls (P < 0.05). Overall, cabergoline treatment increased lactoferrin content of mammary secretions (P = 0.10). The total lactoferrin immunostaining in the mammary tissue increased after drying-off (P < 0.05). Compared with during lactation, this increase was observed at D1 and D8, respectively for cabergoline treated cows and control cows (P

A milk urea model to better assess nitrogen excretion and feeding practice in dairy systems. 20. Nitrogen Workshop

National audience; Chez les vaches laitières, des désordres métaboliques interviennent après la parturition et entraînent des phénomènes inflammatoires. Les cytokines pro-inflammatoires (TNFα, IL1β, IL6) pourraient avoir un effet direct sur la consommation alimentaire, la répartition des nutriments et être liées à une diminution de la production laitière. Différentes molécules à effet anti-inflammatoire, comme le salicylate, utilisées quelques jours après vêlage ont un effet positif à long terme sur la production laitière. Néanmoins, l’utilisation d’anti-inflammatoires dans l’alimentation animale pour stimuler la production de lait n’est pas autorisée. L’utilisation d’extraits de flavonoïdes a permis de montrer qu’ils avaient des effets anti-inflammatoires in vitro et in vivo. Il a également été montré que des extraits de Scutellaria baïcalensis réduisaient, de façon dose-dépendante, les niveaux de TNFα, d’IL1β et d’IL6 chez les animaux traités. Chez la vache laitière, l’extrait de Scutellaria baïcalensis apporté post-vêlage pendant 60 jours dans la ration augmente la production de lait de 230 litres sur l’ensemble de la lactation. Le principe actif de l’extrait de Scutellaria baïcalensis est la baïcaline. Les mécanismes d’action et les cibles cellulaires ne sont pour l’instant pas connus. Le but de cette étude était donc de caractériser in vitro les effets de la baïcaline sur des cellules épithéliales mammaires bovines (CEM) primaires. Des échantillons de tissus mammaires bovins ont été prélevés au pic de lactation (environ 60 jours de lactation) par biopsie, digérés et dissociés pour isoler les CEM correspondant à des cellules sécrétoires matures. Après mise en culture, les CEM ont été soumises à différentes doses de baïcaline en l'absence ou en présence de peroxyde d'hydrogène (H2O2). L'ajout de baïcaline à faibles doses (1 à 10 μg/mL) n'a eu que peu ou pas d'effets positifs sur la prolifération et la viabilité des CEM. A des doses plus élevées (> 50 μg/mL), la baïcaline a diminué la prolifération des CEM (-50%). La baïcaline a également eu un effet anti-apoptotique à faibles concentrations, mais provoqué une apoptose accrue à des doses plus élevées (> 100 μg/mL). Indépendamment des doses de baïcaline utilisées, la production de dérivés réactifs à l’oxygène (ROS) a été diminuée chez les CEM pré-traitées à la baïcaline par rapport aux cellules non traitées (-80%). Ces résultats ont clairement démontré les effets anti-oxydants de la baïcaline sur les CEM. Ceci suggère que la baïcaline à faibles doses (1 à 10 μg / mL) pourrait être utilisée pour prévenir les troubles métaboliques oxydatifs chez la vache laitière.

L’objectif de cet essai est de tester une nouvelle méthodologie pour estimer la valeur protéique des aliments basée sur la réponse biologique des matières protéiques (MP) du lait aux apports en protéines métabolisables de la ration. Par rapport aux méthodes classiques cette méthode peut être appliquée quelle que soit les techniques de protection des protéines appliquées aux aliments (huiles essentielles, tannins végétaux). La prédiction de la valeur protéique d’un aliment testé est réalisée à partir de sa réponse en MP en considérant deux traitements contrôles de valeur protéique connue. Cette réponse n’est pas linéaire du fait que l’efficience d’utilisation des protéines métabolisables décroit lorsque les apports augmentent. N o us avons suppos é que, dans la zone de variation des apports testée, la décroissance de l’efficience est linéaire. Pour développer la méthode, quatre traitements alimentaires isoénergétiques, définis par leurs apports protéiques croissants, ont été appliqués en carré latin pendant quatre périodes de trois semaines à 24 vaches laitières divisées en 6 groupes homogènes de 4 vaches. Les deux traitements contrôles contiennent soit 4,4 kg MS de concentré énergétique (Contrôle Bas (CB), 97 g PDIE/kg MS), soit 3,6 kg MS de tourteaux de soja (Contrôle Haut (CH), 252 g PDIE/kg MS). Les deux traitements intermédiaires, constitué s d’un mélange de ces deux aliments (Medium Bas : MB et Medium Haut : MH), ont été utilisés pour estimer leur valeur en protéines métabolisables à partir de leur réponse en MP. L’accroissement des apports de protéines métabolisables a augmenté la production de MP (896 et 964 g/j pour CB et CH respectivement). L’estimation de la valeur protéique de MB et MH à partir de leur réponse en MP est proche des valeurs calculées avec INRA (2007), mais présente une légère surestimation de respectivement +14 et + 17 g PDIE/kg MS. Ce biais peut être expliqué par le positionnement du régime CH dans la zone haute de la réponse des MP aux apports ce qui correspond à une efficience marginale faible. Un ciblage plus précis de la zone maximale de réponse des MP permet d’ailleurs de réduire ce biais à +7 g PDIE/kg MS pour le traitement MB. Cette limite souligne l’importance à apporter à la formulation des régimes contrôles utilisés de façon à bien cibler la gamme de variation maximale de la réponse en MP. Moyennant cette précaution, l’utilisation de la réponse MP est une approche intéressante pour estimer la valeur protéique des aliments et cela quelles que soient les techniques de protection employées., The aim of this trial is to test a new methodology to estimate feeds protein value based on their milk protein yield (MPY) response to metabolisable proteins supplies in diet. Compared to classical methods, this one could be used whatever the protein protection applied to feeds (essential oils, vegetable tannins). The prediction of the protein value of a tested feed is made from its MPY response using two control treatments of known protein value. This response is not linear because the efficiency of metabolisable proteins decreases as intake increases. We assume that, in the zone of supply variation tested, this decrease in efficiency is linear. To develop the method, four isoenergetic dietary treatments, defined by their increase in protein intake, were applied in a Latin square design of four 3-weeks periods to 24 cows divided in 6 homogenous groups of 4 cows. The two extreme treatments contained either 4.4 kg DM of energy concentrate (Control Low (CL), 97 g PDIE / kg DM) or 3.6 kg DM of soybean meal (Control High (CH), 252 g PDIE / kg DM ). The two intermediate treatments, consisting of a mixture of these two feeds (Medium Low: ML and Medium High: MH), were used to estimate their metabolisable protein value from their response in MPY. The increase in protein supply increased MPY production (896 and 964 g/d for CL and CH respectively). The estimated protein value of ML and MH from their MPY response was respectively +14 and +17 g PDIE / kg DM higher than the values calculated with the feed units system INRA (2007). This bias could be explained by CH position, situated in the upper part of MPY response to protein supplies corresponding to a low marginal efficiency. A more precise targeting of the maximum MPY response zone reduced this bias to +7 g PDIE /kg DM for ML. This limitation emphasizes the importance of diets formulation to target well the range of maximal variation of the MPY response. Nevertheless, the use of the MPY response seems to be an interesting approach for estimating the protein value of feeds, regardless of the protective techniques used.

Over the past decade, the INRA centre in Lusignan has been testing a range of forage solutions. The goal is to improve feed security in dairy systems, which are facing climatic variability and, more specifically, summer droughts. Two main strategies have been explored for producing forage throughout the year in a water- and energy-efficient manner: allowing animals to graze and feeding animals conserved forage. Hem, we discuss methods for extending the grazing season and forage resources by filling the gaps between the mixed temporary grasslands; for example, grains, millet, or stockpiled grassland could be used. We also assess the ability of sorghum and grain-protein crop associations to ensure forage availability. Finally, we examine the results obtained using an experimental low-input forage system, OasYs, that has been in place since 2013. OasYs was specifically designed to deal with climate change and combines several of the solutions discussed., Deux grandes voies complémentaires ont été explorées pour produire des fourrages tout au long de l’année, en économisant l’eau et l’énergie fossile : le pâturage et les fourrages conservés. Nous présentons les résultats obtenus sur des ressources fourragères destinées à allonger la saison de pâturage et à prendre le relai de prairies temporaires diversifiées (céréales, millet, stocks sur pied de couverts prairiaux). L’intérêt du sorgho et des associations céréales-protéagineux pour sécuriser les stocks est également discuté, à partir des différentes modalités que nous avons mises en place. Enfin nous présentons les premiers résultats d’un système fourrager à bas niveau d’intrants, conçu pour être adapté au changement climatique et combinant plusieurs de ces solutions.

Take home message When accurate high throughput monitoring and a steady environment are used, the variability of residual feed intake is only 8% of the variability of energy intake in Holstein cows over a full lactation. Even in these experimental conditions, only 59% out of these 8% are really associated with feed efficiency differences and not with errors. Introduction Reducing the use of resources to maintain production and decrease dairy cow impact on the environment is a major challenge to tackle and is known as improving feed efficiency. Feed efficiency is often estimated with the residual intake defined as the difference between the actual feed intake and the feed intake predicted from the energy consumed or produced by the major biological functions (lactation, body reserves gain and loss and maintenance) (Berry and Crowley, 2013). As residuals of a statistical model, residual intake does not only include feed efficiency differences, but also the accumulated errors of model fitting and errors of measurement. Aggrey and Rekaya (2013) in broilers and Savietto et al., (2014) in beef cattle used a mixed model with random animal effect to isolate the REI only associated with animal feed efficiency differences and not with errors. The objective of the present study was to estimate the part of residual intake variability in dairy cows really associated with feed efficiency differences and less with errors, thanks to a mixed model with random animal effect (Fischer et al., 2017). Material & methods Holstein cows were housed in a free-stall barn and fed with a single TMR based on corn silage and concentrates during the whole lactation. One hundred and nineteen cows were monitored throughout the first 238 days in milk for daily individual feed intake as the difference between offered dry matter and next morning refusals dry matter. All cows were also monitored for morning body weight after milking, daily milk yield, twice a week daily milk protein, fat and lactose, and monthly body condition score with a 0.25 increment scale going from 0 for an emaciated cow to 5 for a fat cow. Feed efficiency was estimated as the residual energy intake (REI): the residual of the linear regression of average net energy intake on average net energy in milk, average metabolic body weight and body condition score gain and loss, both multiplied by average body weight. To estimate the REI associated with feed efficiency and not with errors, the variables used to estimate REI - milk yield and composition, body condition score change, feed intake and body weight - were averaged per 2 week period to create repeated measures per cow during the 238 monitored days. A mixed model was then fitted with random cow-specific slopes for the variables and a random cow-specific intercept. The difference between the energy intake predicted with the cow-specific regression slopes and intercept and the energy intake predicted with the population average slopes and intercept was interpreted as animal variability in feed efficiency and not the error. Results & discussion The variability of REI represented 8% of the variability of the actual net energy intake among the 119 Holstein cows over near the whole lactation. Of this 8% of REI variability, the cow-specific part isolated with the mixed model was only 59%. By definition, this 59% of REI variability is repeatable throughout time and associated with cows, and thus could be considered as feed efficiency differences. However, certain types of errors can be repeatable throughout time and associated with cows, such as sorting feed. The remaining 41% is by definition not repeatably specific to cows throughout time and therefore most probably associated with model fitting errors or measurement errors. However, when temporary events such as clinical mastitis, only affect intake or only affect a biological function, then it is cow-specific, but is not repeatable throughout time and will be included in the error of the mixed model and thus not considered as feed efficiency. Conclusion When using high throughput monitoring of individual feed intake and of the major energy consuming functions in dairy cows fed with a single high energy diet during the whole lactation, residual energy intake differences among Holstein cows are only 8% of the total variability of feed intake. Thanks to a mixed model with cow-specific regression slopes and intercept, we were able to identify that of this 8%, only 59% may be associated with feed efficiency differences and not with model fitting errors or measurement errors.

La fertilité des vaches laitières de race Prim’Holsteinreste actuellement assez faible. Dans une précédente étude (Elis et al., 2016), l'ajout d'acides gras oméga-3 à longue chaîne (AGPI n-3 LC)dans la ration alimentaire de vaches laitières a permis de diminuer le taux de non fécondation-mortalité embryonnaire précoce après la 1èreinsémination artificielle(groupe AGPI n-3 LC 13,5 %, n=22vs témoinn-638,8 %, n=23) suggérant un effet potentiel sur la qualité ovocytaire. Cette étude avait donc pour objectif d’évaluerleseffets de ce même type de supplémentation sur la production d’embryons in vitro chez la vache laitière, après stimulation ovarienne hormonale (superovulation). Ainsi 37 vaches primipares Holstein ont été supplémentées en AGPI n-3 (n=18, huile de poisson micro-encapsulée, 1% MS, OMG750®, Kemin) ou n-6 (n=19, témoin avec huile de soja micro-encapsulée, 1% MS, OMG Soy®, Kemin)à partir de 11 semaines post partum en moyenne et pendant 9 semaines. Des ponctions écho-guidées des follicules ovariens ont été réalisées sur les vaches, après 2, 5 ou 7 semaines de supplémentation. Après ponction folliculaire, les complexes ovocyte-cumulus (COC) ont été mis en maturation, fécondation puis développement in vitro. Au total 1462 follicules ont été ponctionnés sur les vaches n-3 (54 sessions de ponctions) et 1538 follicules sur les vache n-6 (57 sessions). Une augmentation significative du taux de blastocystes jugés de bonne qualité a été observée (p = 0,0217) chez les vaches n-3 (42,7%) comparéesaux vaches témoins n-6 (33,3%), Fertility of Prim’Holstein dairy cowsremains relatively low. In a previous study (Elis et al. 2016), the enrichment of thediet withlong chain n-3 polyunsaturated fatty acids (PUFA n-3 LC) led to a decrease of the non-fertilization–early embryo mortality rateafter the first artificial insemination(PUFA n-3 LC13.5%, n=22 vs controln-638.8%, n=23), suggesting a potential effect on oocyte quality. We thusinvestigated here, the effects of the same supplementation on in vitro embryo production in dairy cows, after ovarian stimulation. Therefore 37 primiparous cows were supplemented witheither n-3 PUFA (n=18, encapsulated fish oil, 1% DM, OMG750®, Kemin) or n-6 PUFA (n=19, control with encapsulated soy oil, 1% DM, OMG Soy®, Kemin). After ovum pick-up, oocyte cumulus complexeswere in vitromatured, fertilized and underwent in vitrodevelopment. A total of 1462 follicles were punctured on n-3 cows (54 sessions) and 1583 follicles on n-6 cows (57 sessions). A significant increase of the good quality blastocystesrate was reported (p = 0.0217) in n-3 cows (42.7%)compared to control n-6 cows (33.3%)

National audience

High prices of milk have encouraged intensive dairying systems using high inputs of chemical fertilisers, indoor feeding with high amounts of concentrate and imported protein at the expense of grazing. Consequently grassland acreage decreased considerably over the last 30 years, and the European dairy systems have become highly dependent on imported fossil energy and proteins. However, the various roles of grassland in providing regulating and supporting services are now widely recognised and grazing ruminants are highly appreciated by the public. This chapter reviews existing knowledge and tools for developing productive, efficient and environmentally friendly dairying systems based on grazing and grassland utilisation. The chapter will consider successively the expected characteristics for the right animal for grassland based systems, the grazing management practises, the supplementation, the more systematic use of legumes in multi species swards and the development of DSS which help farmers to design more efficient grazing management and to find the optimum between the twin objective of high performance by the herd and high rate of herbage utilisation. The chapter concludes by examining the considerable scope for improving animal and grassland performances within grassland-based systems.

Two meta-analysis were conducted to determine; (i) the effects of breed or sex on average daily gain of locale and crossbreds cows originating from Ivory Coast and ( ii), the effect of breed on daily milk yield of these suckled cows. The first analysis showed that the average daily gain of N’Dama breed (482 g/j) is significantly higher than average daily gain of Baoulé breed (304 g/j). Average daily gain of crossbred (Jersiais x N’Dama) cows did not differ with average daily gain of N’dama or Baoulé breeds. No difference between entire and castrated bulls was noted. The second analysis showed that daily milk yield from suckled cows of crossbred (Jersiais x N’Dama) cows (4, 94 kg/j) is higher more daily milk yield from N’Dama or Baoulé cows (2, 05 and 2, 01 kg/j, respectively). However, there is no difference between in the daily milk yield between N’Dama and Baoulé breeds. Analysis confirmed the interest of crossbreeding local Ivory Coast breeds with jersey breed, resulting in increased milk production without any deleterious effect on meat production.

International audience; The urge to reduce antimicrobials use in dairy farming has prompted a search for alternative solutions. As infections of the mammary gland is a major reason for antibiotic administration to dairy ruminants, mammary probiotics have recently been presented as a possible alternative for the treatment of mastitis. To assess the validity of this proposal, we performed a general appraisal of the knowledge related to probiotics for mammary health by examining their potential modes of action and assessing the compatibility of these mechanisms with the immunobiology of mammary gland infections. Then we analyzed the literature published on the subject, taking into account the preliminary in vitro experiments and the in vivo trials. Preliminary experiments aimed essentially at exploring in vitro the capacity of putative probiotics, mainly lactic acid bacteria (LABs), to interfere with mastitis-associated bacteria or to interact with mammary epithelial cells. A few studies used LABs selected on the basis of bacteriocin production or the capacity to adhere to epithelial cells to perform in vivo experiments. Intramammary infusion of LABs showed that LABs are pro-inflammatory for the mammary gland, inducing an intense influx of neutrophils into milk during lactation and at drying-off. Yet, their capacity to cure mastitis remains to be established. A few preliminary studies tackle the possibility of using probiotics to interfere with the teat apex microbiota or to prevent the colonization of the teat canal by pathogenic bacteria. From the analysis of the published literature, it appears that currently there is no sound scientific foundation for the use of probiotics to prevent or treat mastitis. We conclude that the prospects for oral probiotics are not promising for ruminants, those for intramammary probiotics should be considered with caution, but that teat apex probiotics deserve further research.

Better knowledge of pasture utilised by grazing dairy cows (in t DM ha-1 year (y)-1) would help farmers to analyse and improve their grazing management. This is the aim of HerbValo, a generic method designed to be used on commercial farms. This method combines recording grazing or cutting events at paddock level all year round and a spreadsheet for calculating pasture grazed or harvested per rotation and year. For the grazing events, the calculation takes into account the number of grazing days (herd size × residence time) at each rotation and the average daily intake per animal, estimated from a simple description of herd characteristics, supplements, pasture type and quality, and grazing severity. No pasture measurements, such as pre- or post-grazing pasture heights, are required. A large 19-year experimental database (Le Pinau- Haras) was used to calculate the intra- and inter-annual variability of pasture utilisation, according to weather conditions or management practices. Pasture utilisation averaged 9.4 ± 1.32 t DM ha-1 y-1 and ranged from 6.7 to 12.5 t DM ha-1 y-1 depending on paddock, year and management. Using this tool on a number of commercial farms will enable the provision of regional references on pasture utilisation by grazing livestock.

Mammary epithelial cells (MEC) are exfoliated from the epithelium into milk, influencing the number of MEC present in the udder. This process is associated with epithelium integrity. The release of oxytocin (OT) induced by milking causes myoepithelial cell contraction, which, in turn, may stimulate MEC exfoliation through mechanical forces. To investigate the role of OT in MEC exfoliation, we inhibited or induced myoepithelial cell contraction by injecting the OT receptor antagonist atosiban (Ato) or a supraphysiological dose of OT, respectively. Eight cows were assigned to 2 treatments during 2 milkings according to a crossover experimental design: Control+OT (cows were first milked to collect standard milk and then received 5 IU of OT to collect residual milk through a second milking) and Ato + OT (cows were injected with Ato (50 μg/kg of body weight) and milked to collect cisternal milk, then received 5 IU of OT to collect alveolar milk through a second milking). Milk MEC were purified to determine their concentration and number in milk. Mammary epithelium integrity was assessed by measuring the kinetics of plasma lactose concentration. Inhibiting myoepithelial cell contraction by Ato injection decreased the number of exfoliated MEC in milk. In contrast, OT injection increased the concentration of MEC in the residual milk and the number of MEC in the alveolar milk. Ato injection reduced plasma lactose concentration, whereas, in both treatments, OT injections increased it. Our results suggested that myoepithelial cell contraction caused by OT could stimulate MEC exfoliation into milk and was associated with epithelium disruption.