Search

International audience; Methionine (Met) supplementation increases milk, protein and fat yields in cow. We investigated whether this could be partly explained by an increasingflow of milk components in the secretory pathways of mammary epithelial cells. Multiparous Alpine goats at mid lactation (n = 48), grouped by levels of expression of the CSN1S1, were assigned to 4 treatments in a randomized complete block design. Goats were fed a fixed amount of hay and a low (LE, 1.47 Mcal/kg DM) or adequate (AE, 1.54 Mcal/kg DM) energy concentrate combined with 2 levels of metabolizable Met: unbalanced vs. balanced using isopropyl ester of 2-hydroxy-4-methylthio butanoic acid (HMBi 0.24% concentrate DM) to cover 100% of Met requirement, based on cow requirement (INRA, 2007). Treatments were: LE, LEMet (LE, balanced Met), AE and AEMet (AE, balanced Met) for 5 weeks. Goats (23) were slaughtered and mammary tissue was processed for Western blotting using secretory compartment specific markers of membrane traffic. Milk protein yield (P = 0.01) and casein content (P = 0.01) increased in goats fed the Met balanced diets. The amount of the endoplasmic reticulum (ER) markers, Cnx and ERLIN2, decreased (20%, P ≤ 0.05) in goats fed the LE diet. Met balanced diets had the opposite effect on both markers (20%, P ≤ 0.05), as well as on protein disulfide isomerase (45%, P ≤ 0.05). These observations are in agreement with a positive effect of Met on the activity of the ER, the site where protein and lipid are synthesized. On the other hand, a specific marker of the exit site of the Golgi apparatus and secretory vesicles formation (AP1) decreased with the LE diet (25%, P ≤ 0.05) and its highest level was found in goats fed Met balanced diet at AE supply. The higher ßCOP (P = 0.01), a marker of intra Golgi transport, clearly reflected a decrease in membrane transport of LE diets. These data strongly suggest that energy level has a direct impact on membrane traffic in the secretory pathway of mammary epithelial cell while Met improve ER activity and has the tendency to further promote intracellular transport of milk components and, ultimately, their secretion.

International audience; Methionine supplementation is known to modulate milk and protein yields in dairy ruminants. However, the mechanism involved in this phenomenon is still unknown. The cellular and molecular responses in the mammary tissue to methionine (Met) supplementation through HMBi (MetaSmart, Adisseo) at low (LE) and adequate levels (AE) of NEL were investigated according to a 2 × 2 factorial arrangement on 48 multiparous Alpine goats at mid lactation, assigned to a randomized block design in 4 groups during 5 weeks. Each goat was genotyped for CSN1S1 gene to balance each group according to the high or low genotypes for CSN1S1 gene. A fixed amount of hay was distributed per group (1.17 Mcal/kg DM) and a fixed amount of concentrates was distributed individually (1.72 vs. 1.83 Mcal/kg DM in LE and AE, respectively). Metabolizable methionine were 1.95 vs. 2.45% of metabolizable protein in unbalanced (LE and AE) vs. balanced (LEMET and AEMET) diets, respectively. Goats (23) were slaughtered after 5 weeks of treatment. Mammary tissues were collected for the analyses of milk protein mRNA levels by real time RT-PCR and apoptosis by immunohistochemistry using TUNEL assay. A variance analysis was performed with genotype, E, Met and E x Met, E x genotype, Met x genotype interactions as fixed effects and for milk, pre-treatment data yields was used as a covariate. Met supplementation increased milk protein yield (+6.5 g/d; P = 0.03). The treatments did no modify LALBA whereas an interaction E x Met (P = 0.001) were observed for both CSN3 and CSN1S1 mRNA levels showing 2-fold increases with Met supplementation in goats fed AE diet. The supplementation of Met reduced by 51% apoptosis rates in the mammary tissue (P < 0.01). Apoptosis rate was correlated with milk yield (−0.48; P < 0.05). These results suggest that Met increased casein gene expression at AE level and reduced cell death which could partly explain the positive effect of Met supplementation on milk synthesis in the goat mammary tissue.

International audience

To fulfil the requirements for methionine, animal diets are widely supplemented with synthetic methionine sources such as L-methionine (L-Met), DL-methionine (DL-Met), and DL-2-hydroxy-4-(methylthio)-butanoic acid (DL-OH-Met). The objective of this study is to calculate the energy cost of the different conversion steps leading to L-Met and to propose energy equivalence values for DL-Met and DL-OH-Met, relative to that of L-Met. The conversion of DL-OH-Met to L-Met involves a nitrogen-sparing effect, because excess nitrogen can be used for the transformation of DL-OH-Met to L-Met, rather than being excreted as urea or uric acid Consequently, the ME-to-GE ratio of DL-OH-Met is 109% in mammals and 114% in birds, compared to the value of DL-Met. Because of differences in metabolism and the formation of hydrogen peroxide in the conversion to L-Met, the NE-to-ME ratios are 96% for DL-Met and 100% for DL-OH-Met in both mammals and birds. The conversion of DL-OH-Met to L-Met is therefore energetically less costly than the conversion of DL-Met. The stoichiometric approach presented here only considers the biochemical conversion steps, without considering the cost of transport and further transformation steps.

International audience; Methionine (Met) is an essential amino acid (AA) in pigs and the third limiting AA in cereal based diets. Met supplementation improves animal’s performance and protein gain. Besides, Met is considered as an important factor in the control of oxidative status with potential benefits on health and meat quality. This study aimed at investigating the effects of dietary Met provided in excess relative to growth requirements on muscle metabolism in finishing pigs. During the last 14 days before slaughter, crossbred pigs were individually fed diets (13.6% protein, 5.8% fat, 10.8 MJ/kg Net energy, 0.73% Lys) supplemented (Met++) or not (CONT) with OH-Met (n=15 pigs/diet). Dietary Met content was 0.22% and 1.1% in CONT and Met++ diets, respectively. Growth rate, carcass lean meat content and Longissimus muscle (LM) weight at slaughter did not differ between the two groups. In LM, the free AA profile was modified (P

Protein turnover is an energy-consuming process that is essential for ensuring the maintenance of living organisms. Gold standard methods for whole-body protein turnover (WBPT) measurement have inherent drawbacks precluding their generalization for large farm animals and use during long periods. Here, we proposed a non-invasive proxy for the WBPT over a long period of time and in a large number of beef cattle. The proxy is based on the rate at which urine-N and plasma proteins are progressively depleted in terms of15N after a slight decrease in the isotopic N composition of the diet (i.e. diet switch). We aimed to test the ability of this proxy to adequately discriminate the WBPT of 36 growing-fattening young bulls assigned to different dietary treatments known to impact the WBPT rate, with different protein contents (normalv.high) and amino acid profiles (balancedv.unbalanced in methionine). The15N depletion rate found in plasma proteins represented their fractional synthesis rate, whereas the slow depletion rate found in urine was interpreted as a proxy of the WBPT. The proxy tested in urine suggested different WBPT values between the normal- and high-protein diets but not between the balanced and unbalanced methionine diets. In contrast, the proxy tested in plasma indicated that both dietary conditions affected the fractional synthesis rate of plasma proteins. We considered that the rate at which urine is progressively15N-depleted following an isotopic diet switch could be proposed as a non-invasive proxy of the WBPT rate in large farm animals.