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Understanding the evolution of fatty liver metabolism of ducks is a recurrent issue for researchers and industry. Indeed, the increase in weight during the overfeeding period leads to an important change in the liver metabolism. However, liver weight is highly variable at the end of overfeeding within a batch of animals reared, force-fed and slaughtered in the same way. For this study, we performed a proton nuclear magnetic resonance (1H-NMR) analysis on two classes of fatty liver samples, called low-weight liver (weight between 550 and 599 g) and high-weight liver (weight above 700 g). The aim of this study was to identify the differences in metabolism between two classes of liver weight (low and high). Firstly, the results showed that increased liver weight is associated with higher glucose uptake leading to greater lipid synthesis. Secondly, this increase is probably also due to a decline in the level of export of triglycerides and cholesterol from the liver by maintaining them at high hepatic concentration levels. Finally, the increase in liver weight could lead to a significant decrease in the efficiency of aerobic energy metabolism associated with a significant increase in the level of oxidative stress.

International audience; The "Foie gras" or fatty liver is the result of hepatic steatosis from nutritional origin and induced by the force-feeding of palmipeds. Despite identical rearing and force-feeding conditions of ducks from the same breed, different liver weights, within a range of 500 to more than 700 g, are generally observed at the time of evisceration. To better understand the determinism of this large variability in fatty liver weights, the activity of various metabolic pathways has been explored in 4 groups of steatotic livers differing by their weights. Different analyses were performed using biochemical assays on metabolites as well as ELISA tests or enzyme activity assays. The result showed that an increase in the final liver weight is always associated with a hypoxic response and even a severe hypoxia observed in livers with the highest weights (more than 650 g). This is also combined with a rise in the cellular oxidative stress level. In addition, for the heaviest livers (more than 700 g), signs of cell death by apoptosis were also observed, while others programmed cell death pathways , such as ferroptosis or necroptosis, seemed to be nonactive.

The aim of this experiment was to study the effect of chilling rates on the quality features of fatty livers. Three different chilling rates were applied: ultra-fast (UF), fast (FA), and slow (SL). Technological and proteomic results were compared at time T1 when the internal temperature of livers reached 10°C and at time T2 = 24 h post mortem. Samples from the UF group reached the T1 temperature at 50 min post mortem and had the least hard livers and the lowest cooking loss percentage (25 ± 9%) at time T2 = 24 h post mortem (P-value of < 0.01). The FA and SL groups reached the T1 temperature after 120 and 210 min post mortem and presented higher melting (36 ± 9 and 41 ± 9%, respectively, at time T2) and harder livers compared to the UF group. In parallel, we conducted semi-quantifications of proteins by electrophoresis and proteolytic activities by mono-dimensional zymography for three families of proteases: Matrix metalloproteases (MMP), Cathepsins, and Calpains. The proteomic assays revealed less modified proteolytic activities in samples from the UF group, and less associated proteins degradations than in samples from the FA and the SL groups. Effects of the different chilling rates were mainly significant at time T2 (24 h post mortem). As a conclusion we were able to highlight an indirect positive relation between proteolysis and melting yield in ducks' fatty liver.

Background The aim of this study was to analyse the mechanisms that underlie phenotypic quantitative trait loci (QTL) in overfed mule ducks by identifying co-localized proteomic QTL (pQTL). The QTL design consisted of three families of common ducks that were progeny-tested by using 294 male mule ducks. This population of common ducks was genotyped using a genetic map that included 334 genetic markers located across 28 APL chromosomes (APL for Anas platyrhynchos). Mule ducks were phenotyped for 49 traits related to growth, metabolism, overfeeding ability and meat and fatty liver quality, and 326 soluble fatty liver proteins were quantified. Results One hundred and seventy-six pQTL and 80 phenotypic QTL were detected at the 5% chromosome-wide significance threshold. The great majority of the identified pQTL were trans-acting and localized on a chromosome other than that carrying the coding gene. The most significant pQTL (1% genome-wide significance) were found for alpha-enolase on APL18 and fatty acid synthase on APL24. Some proteins were associated with numerous pQTL (for example, 17 and 14 pQTL were detected for alpha-enolase and apolipoprotein A1, respectively) and pQTL hotspots were observed on some chromosomes (APL18, 24, 25 and 29). We detected 66 co-localized phenotypic QTL and pQTL for which the significance of the two-trait QTL (2t-QTL) analysis was higher than that of the strongest QTL using a single-trait approach. Among these, 16 2t-QTL were pleiotropic. For example, on APL15, melting rate and abundance of two alpha-enolase spots appeared to be impacted by a single locus that is involved in the glycolytic process. On APLZ, we identified a pleiotropic QTL that modified both the blood level of glucose at the beginning of the force-feeding period and the concentration of glutamate dehydrogenase, which, in humans, is involved in increased glucose absorption by the liver when the glutamate dehydrogenase 1 gene is mutated. Conclusions We identified pleiotropic loci that affect metabolic pathways linked to glycolysis or lipogenesis, and in the end to fatty liver quality. Further investigation, via transcriptomics and metabolomics approaches, is required to confirm the biomarkers that were found to impact the genetic variability of these phenotypic traits. Electronic supplementary material The online version of this article (doi:10.1186/s12711-017-0313-6) contains supplementary material, which is available to authorized users.

International audience; We investigated liver protease activities to better understand the mechanisms responsible for losses during the cooking of Mule ducks' fatty livers. Fatty livers of similar masses (520 g) were randomly selected among a large flock of overfed male Mule ducks and divided into two groups on the basis of their cooking loss rate, L+ (high cooking losses, 36%) and L (low cooking losses, 21%). In addition to dry matter and total lipid contents, main hepatic protease (matrix metalloproteinase 2, cathepsins, and calpains) activities were measured by zymography. The results show that L+ samples present higher total relative proteolytic activity (6.15 +/- 1.07 vs 4.46 +/- 0.52 for L+ and L- samples, respectively) and total lipid content (61.0 +/- 3.03% vs 53.7 +/- 3.22% for L+ and L- samples, respectively) than L- samples. The results imply that proteases could be involved in the fragilization of the hepatocyte structure, resulting thus in higher cooking losses in L+ samples.

International audience; Fat loss during cooking of duck "foie gras" is the main problem for both manufacturers and consumers. Despite the efforts of the processing industry to control fat loss, the variability of fatty liver cooking yields remains high and uncontrolled. To understand the biochemical effects of postslaughter processing on fat loss during cooking, this study characterizes for the first time the protein expression of fatty liver during chilling using a proteomic approach. For this purpose the proteins were separated according to their solubility: the protein fraction soluble in a buffer of low ionic strength (S) and the protein fraction insoluble in the same buffer (IS). Two-dimensional electrophoresis was used to analyze the S fraction and mass spectrometry for the identification of spots of interest. This analysis revealed 36 (21 identified proteins) and 34 (26 identified proteins) spots of interests in the low-fat-loss and high-fat-loss groups, respectively. The expression of proteins was lower after chilling, which revealed a suppressive effect of chilling on biological processes. The shot-gun strategy was used to analyze the IS fraction, with the identification of all the proteins by mass spectrometry. This allowed identification of 554 and 562 proteins in the low-fat-loss and high-fat-loss groups, respectively. Among these proteins, only the proteins that were up-regulated in the high-fat-loss group were significant (p value = 3.17 X 10(-3)) and corresponded to protein from the cytoskeleton and its associated proteins. Taken together, these results suggest that the variability of technological yield observed in processing plants could be explained by different aging states of fatty livers during chilling, most likely associated with different proteolytic patterns.

Biochemical Research Methods; International audience; In this review, an overview on proteomic studies conducted in livers of farm animals is conducted with a special focus on liver steatosis in waterfowl. Several studies had interest in understanding liver metabolism in dairy cows under various conditions (e.g. fasting) or the evolution of liver proteome during embryonic phases or growing periods in chicken. Those studies provide interesting results leading to a better understanding of the liver metabolism. Liver steatosis development in waterfowl represents a special case and a focus on proteomic studies conducted in these birds will be done. Indeed, recent studies aimed at resolving protein evolution during overfeeding in duck. Proteomic analysis combining two complementary approaches (2-dimensional electrophoresis gels and shot gun strategy) in order to better understand the mechanisms underlying the variability of cooking yield of fatty liver will be presented.

International audience; Fat loss during cooking of duck “foie gras” is the main quality issue for both processors and consumers. Despite the efforts of the processing industry to control fat loss, the variability of fatty liver cooking yield remains high and uncontrolled. To better understand the biological basis of this phenomenon, a proteomic study was conducted. To analyze the protein fraction soluble at low ionic strength (LIS), we used bidimensional electrophoresis and mass spectrometry for the identification of spots of interest. To analyze the protein fraction not soluble at low ionic strength (NS), we used the shotgun strategy. The analysis of data acquired from both protein fractions suggested that at the time of slaughter, livers with low fat loss during cooking were still in anabolic processes with regard to energy metabolism and protein synthesis, whereas livers with high fat loss during cooking developed cell protection mechanisms. The variability in the technological yield observed in processing plants could be explained by a different physiological stage of liver steatosis.