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International audience; In a context of increasing societal concerns around animal production, consumers asks for products coming from grazing dairy systems and. The segmentation of collection rounds to offer milk specifically from these systems results in higher seasonal variability in milk composition that needs to be better understood. Our objective was to characterize the monthly variation of milk and plasma mineral composition and heat stability, in a factorial arrangement of two breeds of cow and three grazing systems. The experiment involved 48 cows, half Holstein-Friesian (HF) and half F1 Jersey Holstein-Friesian crossbred (JFX) at Teagasc Moorepark. The grazing systems were based on either a monoculture of perennial ryegrass, or a perennial ryegrass and white clover sward, or a multispecies pasture. Milk, blood and pasture were sampled monthly between April and June 2021. Milk heat stability increased constantly between April and June and was unaffected by either the breed or the grazing system. Milk Ca, P, Zn and citrate contents were higher with JFX compared with HF, whereas that of Cl was lower. Milk soluble Ca and P contents were unaffected by the breed. Milk contents of a large part of elements (Ca, P, Mg, K, Fe, Cu, Zn, Mn), except Na and Cl, varied strongly according to the month and differently according to the considered element in interaction with the grazing system. No dominant parameters, among those prone to affect milk heat stability, could be clearly related to milk stability results. Plasma contents of all mineral elements, except Fe, strongly increased between April and June, in interaction with the grazing system for inorganic P, Mg and Zn. An important part of this variability could be related to herbage mineral content although plasma mineral contents were not clearly related to milk mineral contents. Funding by SmartCow project (H2020 N°730924) is acknowledged.

International audience; Introduction and aims: Bovine mastitisis an inflammation of the mammary gland generally due to an infection. Itis responsible for considerable economic losses in dairy farms. Preventive and curative strategies that mainly rely on antibiotic therapies are not totally effective and contribute to antibiotic resistance dissemination, prompting the need for alternative or complementary strategies. We previously established a link between teat cistern microbiota composition and bovine mastitisin quarters which had different histories regarding mastitis[1].In thisstudy, to further decipher the relationships between teat cistern microbiota and immune and microbial responses, a switchfrom twice-to once-daily milking (ODM) was used to trigger an udder perturbation. Material and methods: Aswitch to ODM was used in 31initially healthy quarters of dairy cows. Immune and microbial responsesincluding determination of teat microbiotawere monitored just prior to the transition (day 0), and 3 and 14 days following transition to ODM.Results and discussion: Atemporal relationship was reportedbetween initial teat cistern microbiota composition and richness, the immune response to ODM, and mastitis development. Quarters with a low initial microbiota richness and taxonomic markers such as Bacteroidetes and Proteobacteria were associated with a higher rate of mastitis during ODM. Quarters with a higher richness and taxonomic markers such as Firmicutes, Bifidobacteriumand Corynebacteriumdisplayed early inflammation following transition to ODM but without developing mastitis (no infection). Short-term evolution of microbiota indicates that microbiota with a higher initial richness were more strongly altered by transition to ODM, with notably the disappearance of rare OTUs. Microbiota modifications were associated with an early innate immune system stimulation, which, in turn, may have contributed to the prevention of mastitis development[2].These results suggest a role of the bovine teat microbiota composition and richness in the immune response of the mammary gland during perturbations such as transition to ODM or pathogen entrance. They invite us to considerstrategies that can preserve teat microbiota diversityandtaxa associated to a healthy status for the design of next-generation probiotics.

National audience; La mamelle a pour fonction la synthèse et la sécrétion du lait. Cette sécrétion est unidirectionnelle, du compartiment sanguin vers le compartiment luminal, et son volume est principalement régulé par le glucide majeur du lait, le lactose, en raison de son important pouvoir osmotique. Sa synthèse est spécifique de la mamelle et se fait à partir du glucose sanguin capté par la mamelle. Aujourd'hui, certains organismes de conseil en élevage bovin laitier mesurent le taux de lactose du lait en routine dans les laits individuels et étudient la possibilité de l'intégrer comme indicateur dans leurs outils de conseil en élevage. Le taux de lactose du lait serait un indicateur du déficit énergétique, notamment en début de lactation, et de la santé de la mamelle de l'animal. La qualité de cet indicateur repose sur la connaissance et la compréhension qu'on a de ses variations. Du lactose est systématiquement retrouvé dans le sang chez les vaches laitières en lactation et ses variations ont été rarement étudiées. Aussi l'objectif de cette étude est de déterminer en quoi la lactosémie contribue à expliquer la variabilité du taux de lactose du lait. Concrètement, elle consiste à 1) identifier et hiérarchiser les premiers facteurs de variation de la lactosémie; 2) mettre en parallèle ces variations avec celles observées sur le taux de lactose du lait, via l'analyse rétrospective d'une base de données existantes et 3) estimer la quantité de lactose transférée du lait vers le sang via la construction d'un modèle mécaniste. La parité diminue le taux de lactose du lait (-1 ,6 ± 0,3 g/kg) et augmente la lactosémie seulement en fin de lactation (+5, 1 ± 1,7 mg/L). La lactosémie augmente en milieu et fin de lactation chez les multipares (+5, 1 ± 1,1 mg/L). En début de lactation, la quantité de matière grasse à la traite précédente augmente le taux de lactose du lait des multipares(+ 1,01 ± 0,39 g/kg/1 00 g de matière grasse) et la lactosémie des primi- et multipares (+0,60 ± 0,25 g/kg/100 g de matière grasse). L'inflammation mammaire diminue le taux de lactose du lait (-0,2 pour les primi-; -0,4 pour les multipares± 0,1 g/kg/CCS x2) et augmente la lactosémie ( + 1,5 ± 0,2 mg/L/CCS x2 pour les primi- et multipares). Pour une vache Prim'Holstein multipare en début de lactation sans inflammation mammaire et ayant une lactosémie moyenne de 11,9 ± 1,7 mg/L, 2,1 g de lactose traversent l'épithélium mammaire entre deux traites à 12h d'intervalle. Dans ce cas, les variations de la lactosémie entre traites expliqueraient entièrement les variations du taux de lactose du lait. Dans cette étude, nous n'avons pas observé d'effets, ni sur la lactosémie et ni sur le taux de lactose du lait, de la note d'état corporel et du rapport TB!TP, des paramètres qui peuvent être modifiés lors d'un déficit énergétique.

National audience; La restriction alimentaire induit une période de perturbation de l’homéostasie de l’animal pouvant provoquer un déficit énergétique et des troubles de santé chez la vache laitière. Dans le projet casdar BioMarq’Lait, nous recherchons des biomarqueurs non invasifs (dans le lait) dans le but de fournir aux éleveurs un moyen d’identifier précocement les individus nécessitant une attention particulière, afin d’adapter leur alimentation au cas par cas, pour éviter l’apparition de troubles métaboliques et de bien-être. Le lait contient des cellules épithéliales mammaires (CEM) progressivement exfoliées de l'épithélium au cours de la lactation. Le taux d’exfoliation des CEM, correspondant au nombre de CEM exfoliées dans le lait par jour, pourrait représenter un biomarqueur indicateur de l’adaptation des vaches laitières à la restriction alimentaire. Pour tester cette hypothèse nous avons mis en place 2 essais sur vaches laitières. Dans un premier essai, dix-neuf vaches laitières Holstein à 77 ± 5 j de lactation et produisant 40 ± 0.7 kg de lait/j ont été nourries pendant 4 semaines à hauteur de 100 % (groupe témoin, n=9) ou de 80 % (groupe restreint, n=10), de leur matière sèche ingérée ad libitum pendant les deux semaines précédant le début de l’expérimentation. Du lait a été collecté après 5, 9 et 27 jours de restriction afin de purifier les CEM par une méthode d’immuno-séparation magnétique et de déterminer leur concentration. Le taux d’exfoliation des CEM a ensuite été obtenu en multipliant la concentration en CEM dans le lait par le volume de lait produit par jour. La perte de production laitière de 3,5 kg de lait par j (- 9 %) chez les vaches restreintes par rapport aux vaches témoins s’est accompagnée d’une augmentation de 65 % du taux d’exfoliation des CEM dans le lait (P

Once-daily milking (ODM) is known to induce udder inflammation, and could lead to a higher mastitis incidence due to increased milk leakage and extended milk stasis that could promote penetration and multiplication of pathogens. As a fact, ODM increases milk somatic cell counts (SCC) with or without an increased number of clinical mastitis. However, bacteriological analyses are often lacking to describe udder inflammation. Our study aimed to describe the effect of initial health status of the udder on the inflammatory response observed when implementing ODM. The trial used 63 cross-bred Holstein × Normande dairy cows at 78±5 days in milk and comprised a 1-wk control period (cows milked twice daily) and a 3-wk period of ODM (d1, 1st d of ODM). The udder and animal inflammatory status were assessed by measuring SCC 4 d/wk in whole-udder milk, interleukins (IL) 6 and 8 in quarter milk, and haptoglobin in plasma on d0, 1, 2, 3 and 14. The infectious status of quarters was determined at d0, 3 and 14 by milk bacteriological analysis and identification of minor and major pathogens by 16S DNA sequencing. Four initial infectious and inflammatory udder’s classes (57 of the 63 cows) were determined: no infected and inflamed quarters (n=13), no infected quarters but at least one inflamed quarter (n=15), at least one quarter inflamed and infected with a minor pathogen (n=14), and at least one quarter inflamed and infected with a major pathogen (n=15). Milk yield losses due to ODM were higher for cows with inflamed udders compared to non-inflamed udders (25-27% vs 17%, respectively). Implementing ODM increased SCC and IL8. The increase in IL8 was higher for cows infected with a major pathogen. Cows with no infected but inflamed quarters contrasted by showing only a slight increase in SCC with no change in IL8 and haptoglobin. Inflammatory and milk yield responses to ODM thus varied according to the initial udder health status.

Energy deficiency (ED) is known to have many origins on farms (beginning of lactation, climatic conditions…)and to impact dairy cows’ performances. If some indicators regarding ED have been highlighted in the past, theiron-farm use remains unclear and possible use of other indicators or demands on new expectations from both farmers and stakeholders are unknown. Students involved in animal sciences at Agrocampus Ouest (France) led two semi-quantitative surveys in order to collect such information. Stakeholders (vets, specialists in nutrition…; n=14) were exclusively selected from existing network, while farmers (n=67) were selected either from existing networks (n=32) or randomly (n=35). Farmers’ surveys were completed by phone (n=42) or on-farm (n=25). The surveyed holdings were 33 to 320-ha wide, organic (n=13) or not and mainly from western part of France (n=52), the most significant area of dairy farms in the country. 8/67 of farmers were unable to define ED but all knew how to handle this problem when occurring. For both stakeholders and farmers, the sensitive periods were early lactation (33/81) and summer season (32/81). Farmers also included dietary transitions in the sensitive periods (22/67). Almost half of them regularly experienced energy deficiency on their farm (38/67). The most-cited indicator was the change in milk composition (64% of both stakeholders and farmers); the second was body condition score (BCS) (31% of them). Farmers seem to rely more on visual indicators, such as BCS (44/67), coat appearance (7/67) and lameness (4/67), whereas stakeholders prefer to use technical indicators, such as protein (11/14) and fat (4/14) content of milk. Most of them don’t need any additional indicator or tool to follow the energy deficiency (33/81) but they would appreciate to have a more sensitive daily indicator (18/81).

In dairy cattle, underfeeding is known to influence cow’s homeostasis by inducing body reserve mobilization and by reducing milk production. However, its impact on cow’s immune responses is less known. This study aimed to examine blood cell responsiveness to ex-vivo bacterial challenges in cows fed a standard or a low energy diet. Fifty-four Prim’Holstein at mid lactation received a standard diet (based on corn silage) from calving to 201 days in milk, and then were fed a lower energy diet (14.5% concentrates replaced by 11.5% straw and 3% dehydrated alfalfa) for 5 wk. Milk yield was recorded daily. Blood samples collected at wk -2, -1 and 1, 2 and 5 after diet change were incubated ex-vivo with heat-killed Escherichia coli or Staphylococcus aureus bacteria, or saline as a control for 23h at 38.5°C. Plasma Interleukin 8 (CXCL8), an indicator of the inflammatory response, was then measured by ELISA. Plasma haptoglobin, glucose, urea and NEFA concentrations were determined. Data were analysed using a mixed model of variance testing the effect of week with a cow week random effect. The decrease in energy diet content was associated with a loss of 3 kg/d milk yield (P < 0.001) and reduced glucose and urea plasma concentrations (P< 0.01) while plasma NEFA and haptoglobin concentrations did not vary. A higher production of CXCL8 was observed after E. coli and S. aureus stimulations during the underfeeding period (P

International audience; Because of their constant demand for milk, dairy goat subindustries in western France are highly dynamic. Goat systems are rarely feed selfsufficient, so they are greatly affected by any increase in feed prices. In western France, 90% of goats do not graze. This study examined how industry farmers and stakeholders view the role of pastures in goat systems. The surveys revealed that grazing was seen as having benefits (e.g., allowing feed self-sufficiency and meeting societal expectations) as well as disadvantages (especially exposure to parasites). Another challenge is that stakeholders have different ideas about the form that dairy goat farming should take. Some dairies seek to establish certified organic farms based on larger herds. In contrast, those taking over established operations want to put into place small systems that produce farmstead cheese.; Les filières caprines du Grand Ouest sont des filières dynamiques, en demande constante de lait, conventionnel comme biologique. Avec un taux faible d’autonomie alimentaire, les systèmes caprins sont sensibles à une augmentation du coût alimentaire et de la volatilité des prix des matières premières. Le pâturage est un levier potentiel pour améliorer l’autonomie alimentaire à l’échelle des exploitations. Comme 90% des chèvres ne pâturent pas, l’objectif de cette étude est de recueillir la perception des éleveurs et des acteurs de la filière vis-à-vis de la place du pâturage au sein des systèmes caprins. En octobre 2016 et 2017, une enquête semi-quantitative a été réalisée par des étudiants d’Agrocampus Ouest, auprès de l’ensemble des acteurs des filières des régions Poitou-Charentes, Pays de la Loire et Bretagne. Tous les enquêtés s’accordent sur les effets positifs du pâturage sur l’autonomie alimentaire et sur son adéquation avec les attentes sociétales. Mais ils sont aussi en accord sur ses effets négatifs sur la santé des chèvres, dus au parasitisme, qui se révèle comme étant le point technique critique principal, pour les éleveurs comme pour leur encadrement technique. Un autre frein identifié est le décalage entre acteurs concernant l’installation. Certaines laiteries ont une volonté d’installer des cheptels assez importants sous label agrobiologique alors que les reprenants aspirent majoritairement à des systèmes de plus petite taille en système fromager fermier.

Variations of mammary gland (MG) metabolism were studied in dairy cows in response to diets containing 2 levels of net energy of lactation [NEL; 25.0 and 32.5 Mcal/d for low (LE) and high energy (HE), respectively], combined with 2 levels of metabolizable protein [MP, 1,266 and 2,254 g/d of protein digestible in the intestine for low (LP) and high protein (HP), respectively] in a 2 × 2 factorial arrangement. Four cows received 4 diets (LELP, HELP, LEHP, and HEHP) in a 4 × 4 Latin square design with 2-wk experimental periods. Milk production and feed intake were measured on the last 5 d of each period, whereas MG net uptake of AA was determined on d 13. Efficiencies were estimated as the sum of measured milk true protein yield (MPY) and of estimations of metabolic fecal and scurf proteins multiplied by their respective AA profile and divided by the estimated AA supply minus the AA endogenous urinary loss. The increased MPY in the HE compared with the LE diets (higher by 123 g/d) was accompanied by increased mammary plasma flow and MG uptake of the nonessential AA (NEAA) and the essential AA (EAA), except for branched-chain AA. In contrast, the increase in MPY (higher by 104 g/d) observed in the HP compared with the LP diets was linked to increased MG uptake of EAA without a change in mammary plasma flow and a decreased NEAA uptake. Because MG uptake of total AA-N was almost equal to cows' milk output on a nitrogen basis, these different mechanisms involve a large MG flexibility, with variable synthesis of NEAA. In addition, MP efficiency did not increase only through increased MPY in the HE compared with the LE diets but also through metabolic fecal protein, estimated to increase (by 65 g/d) with dry matter intake. The MPY increased in the HP compared with the LP diets, but the increase was smaller than the calculated increase (greater by 993 g/d) in MP supply. The highest MG clearance rates of individual EAA could suggest that Met, His, and Lys were limiting in LP, and Met was the most limiting AA in HP. Interestingly, a similar hypothesis could be stated by analyzing estimated AA efficiencies. The highest efficiencies among EAA, observed for His in HELP and for Met with the other diets, could indicate that they were the most limiting AA in these respective diets, whereas other EAA (including Lys) efficiencies varied with MP efficiency. The MG metabolic flexibility with regard to individual AA utilization partially contributes to the anabolic fate of AA through MPY; however, other export proteins also contribute to variations in MP and AA efficiencies.

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Goat milk chains of Bretagne and Pays de la Loire regions (France) are on a positive dynamic. Due to a low feed self-sufficiency rate (55%) dairy goat systems are sensitive to an increase in feed costs and volatility of agricultural commodities. Pasture is a potential way to improve feeding self-sufficiency. As 90% of goats do not pasture, the present study aims to investigate farmer’s and stakeholder’s perception of grazing in dairy goat. In October 2017, a semi-quantitative survey was performed using 19 farms, 21 chain stakeholders (food supply, advisers, cheese makers and banks), 24 consumers and 3 cheese retailers. The farming systems differed on the size of the flock (from 25 to 1000 goats), the type of farming (13 conventional and 6 organic farms), the main forage used (maize silage (2), hay (9), pasture (6)). All participants agreed with the positive effect of grazing on feed self-sufficiency in farming and being consistent with social expectations by reducing the gap between consumers who believe in farming system based on small grazing flocks and reality. All farmers agreed with the negative effects of grazing on goat health due to parasitism which appears as the main technical issue. However, farmers with a grazing system manage to deal with parasitism, are satisfied with the application of grazing. Other farmers and agricultural advisors consider grazing as technically difficult and it requires high technical skills (parasite and grass offer). Most of milk factories and some farmers think that goats are not suitable for grazing. Grass production is also highly dependent to weather conditions implying day-to-day and seasonal variations of milk production. Only organic milk factories agree on handling hose variations due to grazing systems. Nonetheless, some conventional milk factories point out an improvementof organoleptic qualities of cheese made with milk from pasture. In conclusion, surprisingly, despite the highexpectations from consumers and common interest for feed self-sufficiency through grazing, most of stakeholders remain reluctant to developing grazing in goat systems due to the lack of knowledge and technical advices.

National audience; Les éleveurs bovins laitiers doivent sécuriser leur système d'élevage dans des contextes environnementaux, économiques, sociologiques et techniques devenus fluctuants, en adaptant au plus juste leurs pratiques. Cela se traduit dans certains élevages par une occurrence croissante de perturbations subies par les vaches laitières. La glande mammaire est l’organe responsable de la lactation. Caractériser son adaptabilité est un prérequis pour l’identification puis la sélection d’animaux capables de s’adapter à ces changements. La 1ère vocation de ce travail de thèse était de caractériser l’adaptabilité des vaches laitières en décrivant les réponses interindividuelles de production laitière lors d’une perturbation. La seconde finalité était d’identifier des phénotypes et/ou des génotypes qui modulent les caractéristiques de l’adaptativité. En raison de ses effets locaux, rapides, importants et réversibles sur le fonctionnement de la glande mammaire, l’allongement de l’intervalle entre traites a été choisi comme perturbation de ce fonctionnement. Deux modalités de l'allongement ont été utilisées afin de décrire les phases aigüe et chronique de l’adaptation : un intervalle de traite unique de 24h et 3 semaines de monotraite (n = 724 et 430 données, respectivement). Pour chacune de ces modalités, les 2 composantes de l’adaptabilité, à savoir la résistance et la résilience, ont été respectivement estimées par les pertes de lait lors de l’allongement de l’intervalle entre traites et par le taux de récupération au retour à 2 traites par jour. Suite à un intervalle unique de 24h, les vaches en début de lactation récupèrent plus vite le lait perdu et les primipares ont un taux de récupération supérieur aux multipares. Trois profils de réponse, définis par leur association des modalités de résistance et de résilience, ont été trouvés à l’intervalle unique de 24h. Ces profils étaient caractérisés par la compliance de la glande mammaire (c’est-à-dire son aptitude à se distendre) et par son inflammation. Les réponses de production laitière à 3 semaines de monotraite étaient partiellement déterminées par la génétique de la vache (h2= 0.32 pour les pertes de lait en kg/j et 0.63 pour la récupération de lait (kg/j), respectivement), il pourrait donc être possible de sélectionner les vaches sur ces caractères adaptatifs. Les zones du génome influençant ces réponses étaient en partie différentes de celles contrôlant la production laitière en traite biquotidienne, il est donc possible que le déterminisme génétique impliqué dans les réponses adaptatives soit en partie spécifique à ces dernières. L’enjeu est à présent de déterminer si les réponses adaptatives observées ici avec l’allongement de l’intervalle entre traites sont représentatives des réponses adaptatives que l’on pourrait obtenir avec d’autres perturbations.

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International audience; In INRA (2018) feeding system, the first parameter estimated in response to net energy (E) and metabolizable protein (P) supply is milk protein yield (MPY). Milk yield response is then calculated from the MPY response using a linear function. This suggests an important link between milk protein secretion and milk volume. However, MPY and lactose yield did not respond totally in parallel to E and P supplies (Lemosquet et al. 2010. EAAP pub #127: 177; Daniel et al., 2016. Animal: 1). Indeed, milk volume greatly depends on mammary lactose synthesis, the most important osmotic nutrient synthesized within the mammary epithelial cells. The main precursor of lactose is glucose taken up by the mammary gland. Mammary glucose uptake can also contribute to furnish energy through oxidation. This energy is necessary for milk synthesis. Both mammary protein turnover and milk protein synthesis required ATP as energy. In this presentation, partition of mammary glucose uptake between lactose synthesis and other utilizations (mainly oxidation) will be discussed using results from experiments reporting mammary glucose uptake in response to variations in E and P supplies. Increasing P supply or modifying E supply (via propionate or glucose digestive infusions) both increased whole-body glucose rate of appearance (WBRA, i.e. glucose entry rate from gluconeogenesis, intestinal absorption and glycogenolysis). However, in mid-lactation cows, an increased WBRA did not always increase mammary glucose uptake, lactose and milk yields (Lemosquet et al., 2009. JDS: 3244; JDS: 6068). Mammary glucose uptake and lactose yield both significantly increased in 2 experiments among 3 increasing E or intestinal glucose supplies. It was also the case in 3 experiments among 5 increasing P or AA supply. Interestingly, lactose yield increased once without any increase in mammary glucose uptake in response to P supply (Lemosquet et al., 2009. JDS: 6068). In Haque et al. (2015. JDS: 3951), mammary glucose uptake tended to increase in response to an « ideal » EAA profile while lactose yield did not change. Overall, in the 6 experiments considered an increased glucose uptake led to decrease the lactose: glucose uptake ratio, suggesting an increase in glucose utilization in other pathways than lactose synthesis. Using a biochemical model (Abdou Arbi et al. 2015. BMC Systems Biology: 8), we confirmed the large mammary gland flexibility to oxidize glucose to produce energy or to use glucose toward lactose synthesis. Analyses on mRNA in milk mammary epithelial cells suggested that glucose utilization pathways seemed not strongly regulated at transcription level when E and P supplies varied except if an important decrease of both supplies is induced at the beginning of lactation (Boutinaud et al., 2915. Frontiers in Genetics: 00323). Overall, these data suggest that in mid-lactation cows, increasing milk protein synthesis and mammary glucose oxidation in response to increased E and P supplies could be a priority over increasing in lactose yield.

National audience; La pratique de la monotraite s’accompagne d’une baisse importante de la production laitière ainsi que de changements dans la composition du lait et d’effets rémanents, après 3 semaines, lors du retour à deux traites par jour. De nombreuses études ont montré que les niveaux de production laitière durant la monotraite ainsi que les pertes de production laitière lors du passage à la monotraite varient entre races, et d’une vache à une autre intra race laissant supposer une origine génétique. Dans ce contexte, notre étude visait à estimer les paramètres génétiques de la production laitière et de la composition du lait pendant une phase de monotraite ainsi que des réponses de la production laitière à la monotraite (perte lors du passage à la monotraite et regain au retour à 2 traites par jour), et à identifier des prédicteurs de ces réponses. Notre étude portait sur 430 vaches croisées Holstein X Normande et comprenait 3 périodes: une semaine contrôle à 2 traites par jour, 3 semaines de monotraite et enfin 2 semaines de retour à 2 traites par jour. L’application des 3 semaines de monotraite a diminué la production laitière de 27,5%, les vaches ont récupéré en moyenne 57% du lait perdu lors du retour à 2 traites par jour. Les héritabilités estimées lors de la période contrôle et des 3 semaines de monotraite étaient de 0,41 et 0,35 pour la production laitière, de 0,66 et 0,61 pour le taux butyreux, 0,60 et 0,80 pour le taux protéique, 0,66 et 0,36 pour le taux de lactose et 0,20 et 0,15 pour les scores de cellules somatiques. La production laitière et la composition du lait pendant les périodes de monotraite et de bitraite étaient génétiquement proches avec des corrélations toutes supérieures à 0,80 intra caractère, mais moins qu’entre périodes à même fréquence de traite. Les héritabilités de la perte de lait observée en passant les vaches en monotraite étaient modérées et du même ordre que celle de la production laitière (0,39 et 0,34 respectivement pour la perte de production laitière exprimée en kg/jour et en %). Le regain de production laitière lors du retour à 2 traites par jour était un caractère de forte héritabilité (0,63). La production laitière ainsi que la composition du lait lors de la période contrôle étaient génétiquement corrélées aux réponses mais pas suffisamment pour être considérées comme des prédicteurs des réponses à 3 semaines de monotraite. Les pertes observées lors du premier jour de monotraite étaient corrélées génétiquement à 0,98 et 0,96 avec les pertes de production laitière lors des 3 semaines de monotraite (en kg/jour et en %), et pourraient être ainsi considérées comme des prédicteurs plus précis des pertes de production sur 3 semaines de monotraite.

The quantification of lactoferrin in dairy products is mainly performed using immunological methods (ELISA, radio-immunodiffusion and optical biosensing). These methods are species-specific and considered to be sensitive (ng on a diluted sample basis) but are expensive and reproducibility is average. Separative techniques such as electrophoresis and HPLC can interestingly discriminate different forms of lactoferrin but appeared disappointing for quantification. Indeed, caseins and fat should be removed before analysis, which results in the dilution and loss of lactoferrin, and critical resolution from whey proteins was often observed. In the proposed method, skimmed cow’s milk sample (1 mL) is deposited as is in a microtube containing 100 mg of macroporous cation-exchange sulfonated resin and stirred rotationally for 90 minutes at 20-25 °C. Lactoferrin which is positively charged at the pH of native milk (6.8) is quantitatively adsorbed while the other non-adsorbed negatively-charged whey proteins and caseins are removed by centrifugation. After washing 4 times the resin with 1 ml of water, lactoferrin is quantitatively desorbed after 30 minutes stirring with 1 mL 2M NaCl containing phenylalanine as a dilution marker. Lactoferrin is then completely separated from the co-desorbed cationic peptides and lactoperoxidase using RP-HPLC at 220 nm. This cheap, universal and flexible method improves selectivity (no protein interference) and sensitivity (no dilution) over previous separative methods. Its intra-laboratory validation (six concentrations in triplicate over five days) demonstrated linearity up to 500 μg.mL-1, accuracy (98-110% recovery), sensitivity (LOQ=25 μg.mL-1 milk) and precision (< 4%) which challenge most immunochemical methods. MBRE-HPLC and monoclonal ELISA-sandwich gave similar results for individual raw cow’s milks. Nevertheless different evolutions were observed with milk heated at increasing temperature (60-87° C, 30 s) indicating that the epitope sensitive in ELISA and cationic part implicated in MBREHPLC are situated in different portions of the molecule that are affected differently by heating.

National audience; Améliorer la prédiction de la synthèse des constituants du lait est un enjeu important des systèmes d’alimentation des ruminants. Le système INRA d’alimentation des vaches laitières, s’appuie sur les valeurs des aliments en protéines digestibles dans l’intestin (PDI) et en énergie nette (UFL). Il a été montré que les productions de matières protéiques (MP), de matières grasses (MG) et de lactose augmentent avec les apports PDI et UFL des rations. Réactualisé en 2017, le système INRA prédit la production de MP selon les apports PDI et UFL des rations. Dans ce nouveau système, ni la production de lactose (qui régule le volume de lait) ni celle de MG ne sont prédites en fonction de ce type d’apports. Comme la majeure partie des constituants du lait est synthétisée dans la glande mammaire, étudier le métabolisme mammaire en analysant les prélèvements mammaires des précurseurs et leurs utilisations intra-mammaires permettra de mieux décrire l’effet d’apports alimentaires contrastés en PDI et UFL sur les synthèses de lait. Un essai sur 4 vaches laitières (Prim’ Holstein), en carré Latin 4x4, a testé l’effet de deux niveaux d’apports PDI (1245 vs 2213 g/j) croisés à deux niveaux d’apports UFL (14,2 vs 18,5 UFL/j) pendant des périodes de 2 semaines. Les prélèvements mammaires des principaux précurseurs des constituants du lait (acides aminés [AA], glucose, acétate, b-hydroxybutyrate) ont été comparés aux productions des constituants du lait (somme des AA des protéines synthétisées, lactose, somme des acides gras [AG] synthétisés, glycérol des triglycérides et CO2). Les prélèvements et les productions ont été exprimés en mmol C/h et ont été analysés selon un modèle en ANOVA. La synthèse de protéines du lait augmente de 120 mmol C/h avec les apports PDI des rations. Cette production s’accompagne d’une augmentation similaire des prélèvements d’AA (+ 124 mmol C/h). La production de lactose augmente également de 141 mmol C/h avec les apports PDI ainsi que le prélèvement de glucose (+ 200 mmol C/h), qui a augmenté dans les mêmes proportions (+ 18%). Avec l’augmentation des apports UFL, toutes les synthèses et tous les prélèvements augmentent significativement mais les prélèvements de glucose (+301 mmol C/h), d’acétate et de bhydroxybutyrate (+ 262 mmol C/h) augmentent significativement plus que les synthèses de lactose (+ 124 mmol C/h) et d’AG synthétisés (+ 153 mmol C/h). Dans ce cas, une augmentation importante de la production de CO2 (+ 315 mmol C/h) est observée. Ceci suggère que les nutriments énergétiques prélevés en excès sont orientés vers les voies oxydatives de production de CO2. Ce changement de répartition d’utilisation des précurseurs énergétiques n’est pas observé avec l’augmentation des apports PDI. En réponse aux apports UFL, la mamelle semble donc être un organe de clairance de l’énergie.

International audience; The metabolisable protein (PDI) supplies were revised in the new INRA feeding system (2013). Consequently, the digestible amino acid (AA) supply in the intestine (AADI, in % of PDI) for cattle was to revise since it was developed in 1998. A meta-analysis was performed to estimate the AADI using a close approach to the past method. The new database is larger than the past one (30 publications and 133 diets from 1967 to 1992) since it includes 64 publications (from 1967 to 2013) on cattle and 243 dietary treatments mainly focussed on nitrogen supply (amount or quality). Each dietary AA supply in the duodenum (g/kg DM) was calculated using a linear combination of the rumen undegraded (RUP), the microbial and the endogenous protein flows in the intestine (PI) with the individual feed AA profiles and the two fixed microbial and endogenous profiles, respectively. It was then expressed in % of total AA (i.e. 16 AA). Each relationship between the measured and the calculated AA supply was analysed using a linear model of covariance with a fixed publication effect. The new vs the past models were for the 4 AA recommended in the INRA system: 0.80 + 0.90 × X (RMSE=0.29) vs 1.90 + 0.76 × X (RMSE=0.38) for Lys; 1.03 + 0.45 × X (RMSE=0.17) vs 0.32 + 0.73 × X (RMSE=0.26) for Met; 0.57 +0.79 × X (RMSE=0.24) vs 0.93 + 0.58 × X (RMSE=0.22) for His; 1.78 + 0.86 × X (RMSE=0.32) vs 2.55 + 0.76 × X (RMSE=0.45) for Leu, respectively. The new INRA PI estimations led to lower biases between the measured and the calculated AA supplies compared to the past models since lower RMSE were observed for 15 AA models in addition to a slope closer to one and an intercept closer to zero for 12 AA models. Further analyses will describe the interfering factors influencing the relationships observed for Met, Phe, Arg, Gly, and the RMSE for His. It will be possible to improve the AADI calculations by using these new models to estimate the AA in RUP and microbial PI and the digestibilities of RUP and microbial PI.

International audience; Understanding the dairy cows’ adaptability is of interest to secure dairy systems relative to changes of animals’ environment and breeding. Mammary gland is a key component of cows’ adaptability. To characterize its adaptive potential, its functioning was perturbed by carrying out a single milking interval of 24-h (24h- MI). This study aimed to determine: (1) whether cows’ responses to the 24h-MI could be gathered into typical adaptive profiles; and (2) whether those profiles were influenced by traits describing milk yield and composition, mammary distension, milk flow rate, inflammation, and epithelium integrity. The 24h-MI challenges (n=93) were performed on 56 Holstein-Friesian cows. They consisted of 3 successive periods: 1 wk of twice daily milking (TDM) as a control, 1 single 24h-MI and then 13 d of TDM. PCA followed by clustering revealed 3 profiles of mammary adaptability. Cows in cluster 1 lost on average 4.5 and 6.8 kg/d more milk yield than cows in cluster 2 and 3. Cows in cluster 1 were characterized by showing no increase in milk flow rate and by having the lowest increase in udder teats distance between TDM and 24h-MI day. Thus cows in cluster 1 either lost more milk due to a less compliant udder or had a lesser udder distension because of their substantial milk yield reduction. Cows in cluster 3 recovered on average 63.9% of the milk they had lost, whereas cows in cluster 1 recovered almost completely (90.5%) and cows in cluster 2 recovered completely (100.9%). The lesser recovery observed in cluster 3 might be associated with a lower estimated milk yield potential or an initially inflamed udder (as indicated by a higher occurrence of initial milk interleukin-8 (IL-8), a small cytokine playing a key role in mediating inflammation as it triggers neutrophil recruitment) or both. To conclude, profiles of mammary gland adaptability were discriminated on both milk yield loss and recovery responses and were correlated to some new specific traits: udder compliance, initial udder inflammation status and cow milk yield potential.

National audience; Un travail de méta-analyse a été engagé pour revoir le calcul des valeurs d’acides aminés digestibles dans l’intestin (AADI) dans le projet INRA Systali de révision des systèmes d’alimentation des ruminants. Le calcul des valeurs AADI dépend des calculs des flux de protéines digestibles dans l’intestin d’origine microbienne (PDIM) et alimentaire (PDIA), or ces valeurs ont été modifiées dans Systali. Une nouvelle base de données contenant des essais mesurant les flux d’acides aminés (AA) dans le duodénum a été constituée. La même démarche de calculs que celle choisie par Rulquin et al. (1998, 2001) a été appliquée. La première étape de la démarche a consisté en un calcul théorique des concentrations en AA dans le duodénum basé sur une approche factorielle des flux de PI d’origine microbienne (PIM), alimentaire (PIA) et endogène (PIendo) et de leurs compositions (%) respectives en AA. Ce calcul théorique a alors été confronté aux concentrations mesurées dans le duodénum par la méta-analyse. Des facteurs de correction ont été estimés à partir d’une analyse de covariance avec un effet essai fixe et un modèle linéaire. Les nouveaux modèles ont permis d’améliorer la prédiction des concentrations d’AA mesurées avec des erreurs de prédiction des modèles plus faibles que les modèles passés pour les 16 AA considérés dans le système AADI. De plus, les nouvelles estimations des PI appliquées à la nouvelle base de données ont permis de réduire les biais entre les concentrations calculées et mesurées et d’appliquer des facteurs de correction moins importants. Au final, 15 équations sur 16 (à l’exception de la Phe) présentaient des ordonnées à l’origine plus proche de zéro et des pentes plus proches de 1 que les modèles passés. Les 16 nouvelles équations de correction (incluant celle de la Phe) sont utilisées dans le calcul des 16 valeurs AADI de Systali.

National audience

International audience; In the current uncertain and fluctuating context, identifying adaptable cows is of key importance to secure dairy systems. Adaptable dairy cows could be defined by the elasticity of their mammary gland through its ability to both tolerate disruption and to return to its original state. However, little is known about how to identify those individuals. This study aimed to determine whether a single day ODM challenge could be used to quantify mammary gland elasticity and to explore individual responses profiles, factors of influence and repeatability of these responses. The trial used 292 Holstein-Friesian cows and consisted of 3 successive periods: 1 wk control of twice-daily milking (TDM), one day of ODM, followed by 2 wk of TDM. Cows were split into 10 groups over 5 milk years. The number of observations per cows varied from 1 to 9, with no more than 3 ODM challenges per lactation. Single day ODM generated an average loss of 6.3 kg/d (-21.3%) and an average recovery of 4.8 kg/d was observed when resuming twice-daily milking (TDM). Variability in responses was high among cows (CV=62% and 98% for milk losses and recovery). Clustering lead to the identification of 4 profiles of response, corresponding to different potentials of mammary elasticity. The 4 clusters obtained were well characterized by stage of lactation and potential milk yield level. Repeatability ranged between 33% for milk yield recovery (kg/d) and 57% for milk yield loss (%), suggesting a genetic determinism of the mammary elasticity to single ODM challenge.

International audience

The aim of this study was to compare the modifications in mammary gland metabolism by supplying an ideal versus an imbalanced essential AA (EAA) profile at low and high metabolizable protein (or PDIE, its equivalent in the INRA feeding system). Four lactating, multiparous Holstein cows received 4 treatments composed of 2 basal diets containing 2 levels of PDIE (LP or HP) and 2 different infusions of AA mixtures (AA− or AA+) in the duodenum. The AA+ mixture contained Lys, Met, Leu, His, Ile, Val, Phe, Arg, Trp, and Glu, whereas the AA− mixture contained Glu, Pro, and Ser. The infusion mixtures were iso-PDIE. The diet plus infusions provided 13.9 versus 15.8% of crude protein that corresponded to 102 versus 118 g/kg of dry matter of PDIE in LP and HP treatments, respectively. The treatments were designed as a 2 × 2 crossover design of 2 levels of PDIE supply (LP vs. HP) with 28-d periods. Infusions of AA in the duodenum (AA− vs. AA+) were superimposed to diet within each 28-d period according to 2 × 2 crossover designs with 14-d subperiods. Increasing the PDIE supply tended to increase milk protein yield; however, the efficiency of PDIE utilization decreased and the plasma urea concentration increased, indicating a higher catabolism of AA. The AA+ treatments increased milk protein yield and content similarly at both levels of protein supply. This was explained by an increase in the mammary uptake of all EAA except His and Trp. The mammary uptake of non-EAA (NEAA) was altered to the increase in EAA uptake so that the total AA uptake was almost equal to milk protein output on a nitrogen basis. The ratio between NEAA to total AA uptake decreased from 46% in LPAA− to 40% in LPAA+, HPAA−, and HPAA+ treatments. The PDIE efficiency tended to increase in the AA+ versus the AA− treatments because the NEAA supply and the amount of NEAA not used by the mammary both decreased. Nevertheless, our AA+ treatments seemed not to be the ideal profile: the mammary uptake-to-output ratio for Thr was higher than 1 in LPAA−, but it decreased to 1 in all the other treatments, suggesting that Thr was deficient in these treatments. Conversely, an excess of His was indicated because its uptake was similar in AA+ and AA− treatments. In conclusion, balancing the EAA profile increased milk protein yield and metabolizable protein efficiency at both levels of protein supply by increasing the mammary uptake of EAA and altering the NEAA uptake, leading to less AA available for catabolism.

National audience

"Written in milk" : quel éclairage nous apporte le lait sur la réponse de la cellule épithéliale mammaire lors du passage à la monotraite ?. 13. Journées de l'Animation transversale "Glande mammaire, lait"

"Chantier qualité spécifique "Auteurs Externes" département de Génétique animale : uniquement liaison auteur au référentiel HR-Access "; absent

Séance : Capacité d’adaptation des exploitations d’élevage; L’allongement de l’intervalle entre traites peut répondre aux attentes des éleveurs laitiers qui doivent faire face à une faible disponibilité en main d’oeuvre en lien avec un travail d’astreinte conséquent (Pomiès et al., 2008). Cette pratique lorsqu’elle est poussée à l’extrême (24h d’intervalle entre traites) provoque des baisses de production laitière telles, que son développement dans les élevages repose sur l’identification d’individus adaptés, basée sur la mesure précoce de phénotypes prédicteurs. Alors que l’hypothèse d’une régulation mécanique de la production laitière en réponse à cet allongement de l’intervalle entre traites prédomine dans la littérature, aucun phénotype à valeur prédictive de ce type n’a été mis en évidence jusqu’à maintenant. La présente étude a pour objectif d’identifier des premiers phénotypes issus de cette régulation mécanique. Les vaches laitières s’adaptant dès le 1er jour à l’allongement de l’intervalle entre traites, l’étude consiste à décrire la réponse des animaux en utilisant un intervalle unique de 24h.

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Session : Production, Management and the Environment: Management and Methods; Extended milking intervals can reduce milk yield but this response is highly variable among cows. Identifying cows with the low milk yield loss associated with milking interval is difficult, restricting the development of milking practices such as once-daily milking. A trial was carried out to identify phenotypic predictors linked to a physical regulation of milk yield due to milk accumulation in the udder. Thirty-two primi- and multiparous Holstein cows producing 34.1 ± 5.4 kg/d of milk at 184 ± 29 d in milk were milked twice a day at 0700 and 1600 h during the 7-dcontrol period (C) and then morning milking was omitted one day (MO, milking omission). Indeed milk loss was shown to occur very rapidly, from the 1st day of implementation. Milk yield and flow were recorded at each milking. Milk fat, protein, lactose, and cell contents were analyzed at each milking for 3 consecutive days of the control period, and on the MO day. Lactose was analyzed in tail blood samples collected 1 h before milking 2 d before MO and on MO day; distances between the 4 teats tips were also measured 1h before milking. Data were analyzed to determine Pearson correlations using SAS. Milk yield decreased by 6.8 kg/d (20%) in response to MO (P = 0.0001). The absolute and relative milk losses showed high variability between cows (−0.1 to 13.4kg/d and −0.5 to 42%, resp.). Milk loss (absolute or relative) was not correlated to C milk yield. Absolute milk loss was negatively but poorly correlated with C milk fat and protein content (r = −0.34 and −0.40; P = 0.05) and positively but poorly also with C milk lactose content (r = 0.33; P = 0.06). Milk loss was not correlated with C plasma lactose levels and the C total distance between tips. Absolute milk loss was positively correlated to C milk average flow (r = 0.59 and 0.46, resp.; P < 0.01) and negatively to C milking time (r = −0.58; P < 0.001). Inconclusion, milk flow could be a promising key phenotypic predictor of individual milk yield losses in response to once-daily milking and in relation to physical regulation of milk secretion.

International audience

Measurement of the immunoglobulin G concentration of dairy cow colostrum. A study was conducted to see if the concentration of colostral immunoglobulin G (IgG) in Holstein dairy cows differed according to the sampling method. Concentrations of IgG were measured by radial immune-diffusion (RID). Three sampling regimens were tested: composite sample, single sample and time of sampling. IgG was measured in: a composite sample (taken from the 4 quarters of the udder at first milking in 78 cows),in a single sample (taken from 1 quarter at first milking in 78 cows) or in several samples, 7 to 9 samples taken through out the duration of first milking in 9 cows, to test a potential ‘time of sampling’ effect. In conclusion, at the level of 50 g/L, which is considered to be “good quality” or acceptable colostrum, the concentration of IgG was unaffected by sampling time or sampletype. Based on the calves’ capacity to drink, observed in the present study, it is recommended that 2 to 4 L of colostrum be consumed within 2 hours of birth and that colostrum should be collected preferably from the posterior quarters. The quantity given is crucial due to the quality of dairy cow colostrum.; Une étude a été menée pour savoir si l’évaluation de la teneur en immunoglobulinesG (IgG) du colostrum chez la vache laitière Prim’Holstein différait, selon qu’elle se réalisait sur un échantillon de lait composite des quatre quartiers issus de la première traite (pratique courante), sur le lait issu d’un seul quartier, ou à plusieurs moments de la première traite. La teneur en IgG a été mesurée sur 78 vaches par immuno-diffusion radiale(IDR), à la fois sur un échantillon prélevé de la première traite des 4 quartiers(lait composite) et sur un échantillon des autres quartiers. De plus,9 vaches ont fait l’objet de 7 à 9 prélèvements en cours de première traite pour évaluer un effet potentiel « moment du prélèvement ». Il ressort qu’au seuil de 50 g/L pour considérer un colostrum de « bonne qualité »ou de qualité acceptable, il n’y avait aucune influence ni du moment de prélèvement, ni du type de prélèvement, sur la mesure de la teneur enIgG. Compte tenu de la capacité de buvée des veaux observée dans l’étude, il peut être recommandé de donner 2 à 4 litres dans les 2 premières heures de vie du veau, le colostrum pouvant être collecté préférentiellement des quartiers postérieurs. La quantité administrée est cruciale en raison de la qualité des colostrums de vaches laitières.

Session 14. Genetic control of adaptation; absent

Most dairy cows throughout the world are milked twice daily. In intensive dairying systems, however, it is not uncommon to increase milking frequency to between 3 and 6 times daily to increase milk production. Reducing milking frequency is much less common; however, once-daily milking of dairy cows, practiced either strategically during certain parts of the lactation or for the entire lactation, is not uncommon in key dairying countries where less emphasis is placed on milk production per cow. The practice fits well with more extensive dairy production systems, particularly those based on grazed pasture. A feature of once-daily milking is that it reduces milk yield by approximately 22%, depending on stage of lactation, breed, and parity, and it may adversely affect lactation length and persistency. However, it can offer several positive farm management options, especially related to labor requirements and farm working expenses. In addition, it may provide a tool to better manage the metabolism and energy balance of cows during early lactation or during periods of pasture deficit, and it may help to improve reproductive performance and animal health and welfare. Once-daily milking, representing one extreme of the mammary function spectrum, has attracted considerable research interest over the years. Consequently, substantial scientific information is available on its effects on mammary function, at both the physiological and molecular levels. This review focuses instead on the management of the cow milked once daily, covering the production response in relation to breed, stage of lactation, and parity, and its effect on energy status, reproduction, health and welfare, as well as on milk composition and processability.

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National audience; L’omission d’une traite par jour entraîne, chez la vache laitière, une importante perte de production suivie d’un effet rémanent négatif lors du retour à 2 traites par jour, après 3 semaines de monotraite. La perte de production lors du passage à 1 traite/j est très variable entre animaux (Rémond et Pomiès, 2005), rendant difficile une prévision. L’identification, et plus encore la sélection d’animaux aptes à supporter la monotraite nécessite de mesurer un phénotype corrélé aux 2 aspects de cette aptitude (perte, effet rémanent), facilement mesurable en ferme et assez tôt dans la lactation. La présente étude a pour objet de décrire la variabilité entre individus des 2 aspects de l’aptitude à la monotraite, et aussi d’identifier des premiers phénotypes prédicteurs

International audience; The quantity of milk accumulated in the udder, under extended milking intervals, could reduce milk yield, with residual effects on following milking intervals. Aim of the trial was to modify the quantity of milk stored in the udder over one milking interval, by decreasing udder emptying (100, 70, 40, and 0% ), in order to describe the short-term effects on milk yield and composition. 16 dairy cows averaging 41 kg/d of milk were assigned to treatments 100, 70, 40, and 0% according to a Latin square design with four 7 -d periods. Cows were milked twice daily at 0700 and 1730. Treatments were applied at the morning milking called MO. Changes in milk yield and composition were assessed on the 7 following milking (Ml to M7), using the mixed procedure of SAS with milking as repeated measures. The quantity of milk collected at Ml milking linearly increased as udder emptying decreased at MO. Nevertheless, because of milk accumulation in the udder, MO+Ml milk yield was quadratically depressed by -1.5, -5.3, -12.9 kg with 70,40 and 0% treatments, respectively. Residual effects on milk yield were only observed for 40 and 0% treatments on M2 and M3 milking and did not differ between 40 and 0% treatments. Milk fat content increased only for treatment 0% at Ml and for treatments 40 and 00/o at M2. Milk lactose content was lower for treatments 40 and 0% at Ml and only for treatment 0% till M4. Lower milk: protein contents were observed from M2 till M5 milking for either treatment 40 or 0% or both. Till M5 milking, somatic cell score linearly increased as udder emptying decreased at MO. In conclusion, a 70%-emptying milking at one milking did not alter milk yield and composition in dairy cows. Residual effects on milk yield and composition were only observed for higher amounts of milk: accumulated in the udder.

Gluconeogenesis, mammary metabolism and their links with milk production in lactating dairy cows

International audience

National audience

International audience; In lactating dairy cows, yields of milk lactose and protein increase in response to increasing supply of intestinal protein or glucogenic nutrients (GN: ruminal infusion of propionic acid or post-ruminal infusion of glucose), but to a different extent. What are the common and the different changes in mammary metabolism explaining that both type of nutrients (protein or GN) increased both yields of protein and lactose? To answer this question a meta-analysis on mammary uptake data was performed. To analyse intra mammary metabolism and to estimate the requirement and supply of ATP to support the increases in milk synthesis, a modelling approach was performed on one study. Increased protein yield was associated with an increase in mammary net uptake of AA from group I (His, Met, Phe+Tyr), in response to extra protein or extra GN. However, this increased uptake was achieved differently. In response to protein supply, it was linked to an increase in mammary arteriovenous differences whereas in response to GN, it was linked an increase (tendency) in mammary plasma flow. In response to increasing protein supply, the mammary uptake of essential AA from group II (Ile, Lys, Leu and Val) as well as their ratio of mammary uptake to milk output (>1) also increased. This brought extra carbon skeletons and nitrogen for mammary synthesis of other components as non essential AA (NEAA), whereas the mammary uptake of two NEAA, Ala and Glu decreased. By contrast, NEAA uptakes (Ala and Glu) increased in response to GN supply (quadratic effect). Milk fatty acid synthesis was only increased in response to increasing protein supply, supported by an increase in b-hydroxybutyrate (BHBA) uptake. If lactose yield increased in parallel to milk protein yield both in response to protein or GN supply, glucose uptake did not follow lactose yield. Mammary glucose partition between lactose and oxidative pathways seemed a key mechanism to explain the increased lactose yield, in particular in response to GN supply. The increased protein synthesis was the only synthesis that required a substantial increase in ATP production, based on the modelling approach. The extra ATP required could be supplied by the catabolism of BHBA and group II AA in response to protein or the catabolism of extra glucose and lactate in response to GN supply. This meta-analysis confirms that the increase in uptake of AA from group I is a common mechanism to support an increase in milk protein yield. It also confirms that the regulation of the partition of their precursors (acetate, glucose, BHBA, group II AA and NEAA) towards milk components synthesis or oxidation is probably one of the key factors in the regulation of milk volume and composition.

International audience

International audience

International audience