Au pâturage, des indicateurs pour faciliter les décisions de sortie de parcelles des vaches laitières

La gestion du pâturage se raisonne à l’échelle del’ensemble de la sole pâturée mais aussi au niveau dela parcelle en cours de pâturage. Concrètement, dansle cas du système de pâturage tournant, la question estde savoir : quand sortir les vaches laitières de laparcelle ? La hauteur d’herbe résiduelle peut êtreutilisée pour aider à la prise de décision en matière desortie de parcelle. L’objectif de ce texte est de proposerdiverses relations entre hauteur en entrée (HE) etsortie (HS) de parcelle obtenues grâce à une gestiondes parcelles basée sur les performances animales

Quelle vache laitière pour quel système ?

Satellite 3Rabsen

Compact-calving systems are better suited to dual-purpose than dairy cow breeds, particularly when nutrient supply is limited

This study aimed to explore adaptive trajectories of dairy and dual purpose breeds in contrastinggrazing-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 progesteroneinformation (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 conditionthan in the High FS. NO resumed ovarian activity earlier (-5 d) and showed a higher proportion ofnormal cyclicity patterns (+22%) than HO. There was no difference in ovulation detection rates betweenbreeds or FS. The NO had a higher re-calving rate than HO (+19%). Feeding system was not associatedwith cyclicity and re-calving rate. By limiting their milk yield, NO did not experience a severe negativeenergy balance, unlike HO. This resulted in better reproductive performance for NO, suggestive ofgreater suitability to a compact calving system

Compact-calving systems are better suited to dual-purpose than dairy cow breeds, particularly when nutrient supply is limited

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

Effect of breed, energy level of diet, and lactation stage on the evolution of milk lipolysis in dairy cow

International audienceSpontaneous lipolysis is the result of the activity of a native milk enzyme, the lipoprotein lipase. Lipolysis leads to a release of free fatty acids(FFA) that cause rancid flavor in milk products. A trial was carried out to study the effects of breed, energy levels, and lactation stage on milkspontaneous lipolysis in dairy cows. Sixty-four cows were used through a year of lactation. Cows were divided into 4 homogenous groups according to their breed [Holstein (HO) or Normande (NO)] and to their feeding system: the intensive system, with a high energy diet (HED) (in winter, corn silage with 30% concentrate; otherwise, pasture with 4 kg/d of concentrate) and the grass system (GS) (in winter, conserved grass with no concentrate; otherwise, pasture with no concentrate). The period of calving was synchronized between January and March. Individual milk samples were collected every month from both morning and evening milkings. The FFA levels were determined by the difference betweenthe FFA levels after milking and the FFA after 24 h of storage at 4°C. Data were analyzed using SAS mixed procedure. We showed that FFAlevels were higher in the evening milks (0.45 vs. 0.25 mEq/100 g of fat, P < 0.001) and that evening milks were more susceptible to lipolysisvariations. HO cows were more susceptible to lipolysis than NO (0.34 vs. 0.20 mEq/100 g of fat, in morning milks; 0.62 vs. 0.33 mEq/100 gof fat in evenings milks, P < 0.001). There was no effect of the feeding system on morning milks lipolysis but GS had a tendency to increase milk lipolysis in evening milks (0.41 vs. 0.55 mEq/100 g of fat, P = 0.06). Lipolysis was higher in early and late lactation stage, particularly in the GS group. Conserved grass may also affect the lipolysis rate. The energy status in early and late lactation stage is frequently negative so the cows may be more susceptible to a low energy diet. No correlation was found between lipolysis and milk fat content. Poor correlations (r < 0.4, P < 0.001) were found between lipolysis and milk production, fat globule size, proportion of fatty acid and protein composition, body condition and weight

HerbValo – a method for calculating annual pasture utilisation by dairy cows at paddock level

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

The robustness of dairy cows analyzed through the profiles of their adaptive responses

International audienc

Probing heterotrimeric G protein activation: applications to biased ligands.

International audienceCell surface G protein-coupled receptors (GPCRs) drive numerous signaling pathways involved in the regulation of a broad range of physiologic processes. Today, they represent the largest target for modern drugs development with potential application in all clinical fields. Recently, the concept of "ligand-directed trafficking" has led to a conceptual revolution in pharmacological theory, thus opening new avenues for drug discovery. Accordingly, GPCRs do not function as simple on-off switch but rather as filters capable of selecting the activation of specific signals and thus generating texture responses to ligands, a phenomenon often referred to as ligand-biased signaling. Also, one challenging task today remains optimization of pharmacological assays with increased sensitivity so to better appreciate the inherent texture of ligands. However, considering that a single receptor has pleiotropic signaling properties and that each signal can crosstalk at different levels, biased activity remains thus difficult to evaluate. One strategy to overcome these limitations would be examining the initial steps following receptor activation. Even, if some G protein independent functions have been recently described, heterotrimeric G protein activation remains a general hallmark for all GPCRs families and the first cellular event subsequent to agonist binding to the receptor. Herein, we review the different methodologies classically used or recently developed to monitor G protein activation and discussed them in the context of G protein biased-ligands

Is selecting dairy cows for fat and protein contents an opportunity to maintain yearly compact-calving systems?

This study aimed to explore the effect of alternative selection strategies based on milk fat and proteincontents instead of milk yield on reproduction of dairy cows. About 500 lactations were recorded, equallydistributed among breeds (Holstein: HO or Normande: NO) and genetic groups with similar geneticmerit for fat and protein yields and either high breeding values for milk yield (MILK) or fat and proteincontents (CONT). Milk progesterone monitoring enabled the study of the reproductive performance. Inboth 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-1in NO) than cows in MILK. Cows in CONT had an earlier resumption of luteal activity than cows inMILK (-6 d in HO, -4 d in NO). There was no difference in ovulation detection rates between geneticgroups. 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 andprotein contents may not be a good opportunity to improve reproduction

Effect of breed, energy level of diet, and lactation stage on the evolution of milk lipolysis in dairy cow

Spontaneous lipolysis is the result of the activity of a native milk enzyme, the lipoprotein lipase. Lipolysis leads to a release of free fatty acids (FFA) that cause rancid flavor in milk products. A trial was carried out to study the effects of breed, energy levels, and lactation stage on milk spontaneous lipolysis in dairy cows. Sixty-four cows were used through a year of lactation. Cows were divided into 4 homogenous groups according to their breed [Holstein (HO) or Normande (NO)] and to their feeding system: the intensive system, with a high energy diet (HED) (in winter, corn silage with 30% concentrate; otherwise, pasture with 4 kg/d of concentrate) and the grass system (GS) (in winter, conserved grass with no concentrate; otherwise, pasture with no concentrate). The period of calving was synchronized between January and March. Individual milk samples were collected every month from both morning and evening milkings. The FFA levels were determined by the difference between the FFA levels after milking and the FFA after 24 h of storage at 4°C. Data were analyzed using SAS mixed procedure. We showed that FFA levels were higher in the evening milks (0.45 vs. 0.25 mEq/100 g of fat, P < 0.001) and that evening milks were more susceptible to lipolysis variations. HO cows were more susceptible to lipolysis than NO (0.34 vs. 0.20 mEq/100 g of fat, in morning milks; 0.62 vs. 0.33 mEq/100 g of fat in evenings milks, P < 0.001). There was no effect of the feeding system on morning milks lipolysis but GS had a tendency to increase milk lipolysis in evening milks (0.41 vs. 0.55 mEq/100 g of fat, P = 0.06). Lipolysis was higher in early and late lactation stage, particularly in the GS group. Conserved grass may also affect the lipolysis rate. The energy status in early and late lactation stage is frequently negative so the cows may be more susceptible to a low energy diet. No correlation was found between lipolysis and milk fat content. Poor correlations (r < 0.4, P < 0.001) were found between lipolysis and milk production, fat globule size, proportion of fatty acid and protein composition, body condition and weight